2008 : WHAT HAVE YOU CHANGED YOUR MIND ABOUT? WHY?

I have changed my mind about the nature of perception. I thought that a goal of perception is to estimate properties of an objective physical world, and that perception is useful precisely to the extent that its estimates are veridical. After all, incorrect perceptions beget incorrect actions, and incorrect actions beget fewer offspring than correct actions. Hence, on evolutionary grounds, veridical perceptions should proliferate.

Although the image at the eye, for instance, contains insufficient information by itself to recover the true state of the world, natural selection has built into the visual system the correct prior assumptions about the world, and about how it projects onto our retinas, so that our visual estimates are, in general, veridical. And we can verify that this is the case, by deducing those prior assumptions from psychological experiments, and comparing them with the world. Vision scientists are now succeeding in this enterprise. But we need not wait for their final report to conclude with confidence that perception is veridical. All we need is the obvious rhetorical question: Of what possible use is non-veridical perception?

I now think that perception is useful because it is not veridical. The argument that evolution favors veridical perceptions is wrong, both theoretically and empirically. It is wrong in theory, because natural selection hinges on reproductive fitness, not on truth, and the two are not the same: Reproductive fitness in a particular niche might, for instance, be enhanced by reducing expenditures of time and energy in perception; true perceptions, in consequence, might be less fit than niche-specific shortcuts. It is wrong empirically: mimicry, camouflage, mating errors and supernormal stimuli are ubiquitous in nature, and all are predicated on non-veridical perceptions. The cockroach, we suspect, sees little of the truth, but is quite fit, though easily fooled, with its niche-specific perceptual hacks. Moreover, computational simulations based on evolutionary game theory, in which virtual animals that perceive the truth compete with others that sacrifice truth for speed and energy-efficiency, find that true perception generally goes extinct.

It used to be hard to imagine how perceptions could possibly be useful if they were not true. Now, thanks to technology, we have a metaphor that makes it clear — the windows interface of the personal computer. This interface sports colorful geometric icons on a two-dimensional screen. The colors, shapes and positions of the icons on the screen are not true depictions of what they represent inside the computer. And that is why the interface is useful. It hides the complexity of the diodes, resistors, voltages and magnetic fields inside the computer. It allows us to effectively interact with the truth because it hides the truth.

It has not been easy for me to change my mind about the nature of perception. The culprit, I think, is natural selection. I have been shaped by it to take my perceptions seriously. After all, those of our predecessors who did not, for instance, take their tiger or viper or cliff perceptions seriously had less chance of becoming our ancestors. It is apparently a small step, though not a logical one, from taking perception seriously to taking it literally. 

Unfortunately our ancestors faced no selective pressures that would prevent them from conflating the serious with the literal: One who takes the cliff both seriously and literally avoids harms just as much as one who takes the cliff seriously but not literally. Hence our collective history of believing in flat earth, geocentric cosmology, and veridical perception. I should very much like to join Samuel Johnson in rejecting the claim that perception is not veridical, by kicking a stone and exclaiming "I refute it thus." But even as my foot ached from the ill-advised kick, I would still harbor the skeptical thought, "Yes, you should have taken that rock more seriously, but should you take it literally?"

Sometimes the later Roman empire seems very long ago and far away, but at other times, when we explore Edward Gibbon's famous claim to have described the triumph of "barbarism and religion", it can seem as fresh as next week.  And we always know that we're supposed root for the Romans.  When I began my career as historian thirty years ago, I was all in favor of those who were fighting to preserve the old order.  "I'd rather be Belisarius than Stilicho," I said to my classes often enough that they heard it as a mantra of my attitude — preferring the empire-restoring Roman general of the sixth-century to the barbarian general who served Rome and sought compromise and adjustment with neighbors in the fourth.  

But a career as a historian means growth, development, and change.  I did what the historian — as much a scientist as any biochemist, as the German use of the word Wissenschaft for what both practice — should do:  I studied the primary evidence, I listened to and participated in the debates of the scholars.  I had moments when a new book blew me away, and others when I read the incisive critique of the book that had blown me away and thought through the issues again.  I've been back and forth over a range of about four centuries of late Roman history many times now, looking at events, people, ideas, and evidence in different lights and moods.

What I have found is that the closer historical examination comes to the lived moment of the past, the harder it is to take sides with anybody.  And it is a real fact that the ancient past (I'm talking now about the period from 300-700 CE) draws closer and closer to us all the time.  There is a surprisingly large body of material that survives and really only a handful of hardy scholars sorting through it.  Much remains to be done:  The sophist Libanius of Antioch in the late fourth century, partisan for the renegade 'pagan' emperor Julian, left behind a ton of personal letters and essays that few have read, only a handful have been translated, and so only a few scholars have really worked through his career and thought — but I'd love to read, and even more dearly love to write, a good book about him someday.  In addition to the books, there is a growing body of archaeological evidence as diggers fan out across the Mediterranean, Near East, and Europe, and we are beginning to see new kinds of quantitative evidence as well — climate change measured from tree-ring dating, even genetic analysis that suggests that my O'Donnell ancestors came from one of the most seriously inbred populations (Ireland) on the planet — and right now the argument is going on about the genetic evidence for the size of the Anglo-Saxon migrations to Britain.  We know more than we ever did, and we are learning more all the time, and with each decade, we get closer and closer to even the remote past.  

When you do that, you find that the past is more a tissue of  choices and chances than we had imagined, that fifty or a hundred years of bad times can happen — and can end and be replaced by the united work of people with heads and hearts that makes society peaceful and prosperous again; or the opportunity can be kicked away.  

And we should remember that when we root for the Romans, there are contradictory impulses at work.  Rome brought the ancient world a secure environment (Pompey cleaning up the pirates in the Mediterranean was a real service), a standard currency, and a huge free trade zone.  Its taxes were heavy, but the wealth it taxed so immense that it could support a huge bureaucracy for a long time without damaging local prosperity.  Fine:  but it was an empire by conquest, ruled as a military dictatorship, fundamentally dependent on a slave economy, and with no clue whatever about the realities of economic development and management.  A prosperous emperor was one who managed by conquest or taxation to bring a flood of wealth into the capital city and squander it as ostentatiously as possible.  Rome "fell", if that's the right word for it, partly because it ran out of ideas for new peoples to plunder, and fell into a funk of outrage at the thought that some of the neighboring peoples preferred to move inside the empire's borders, settle down, buy fixer-upper houses, send their kids to the local schools, and generally enjoy the benefits of civilization.  (The real barbarians stayed outside.)  Much of the worst damage to Rome was done by Roman emperors and armies thrashing about, thinking they were preserving what they were in fact destroying.

So now I have a new mantra for my students:  "two hundred years is a long time."  When we talk about Shakespeare's time or the Crusades or the Roman Empire or the ancient Israelites, it's all too easy to talk about centuries as objects, a habit we bring even closer to our own time, but real human beings live in the short window of a generation, and with ancient lifespans shorter than our own, that window was brief.  We need to understand and respect just how much possibility was there and how much accomplishment was achieved if we are to understand as well the opportunities that were squandered.  Learning to do that, learning to sift the finest grains of evidence with care, learning to learn from and debate with others — that's how history gets done.  

The excitement begins when you discover that the past is constantly changing.

Mentors, paper referees and grant reviewers have warned me on occasion about scientific "fishing expeditions," the conduct of empirical research that does not test a specific hypothesis or is not guided by theory. Such "blind empiricism" was said to be unscientific, to waste time and produce useless data. Although I have never been completely convinced of the hazards of fishing, I now reject them outright, with a few reservations.

I'm not advocating the collection of random facts, but the use of broad-based descriptive studies to learn what to study and how to study it. Those who fish learn where the fish are, their species, number and habits. Without the guidance of preliminary descriptive studies, hypothesis testing can be inefficient and misguided. Hypothesis testing is a powerful means of rejecting error — of trimming the dead limbs from the scientific tree — but it does not generate hypotheses or signify which are worthy of test. I'll provide two examples from my experience.

In graduate school, I became intrigued with neuroembryology and wanted to introduce it to developmental psychology, a discipline that essentially starts at birth. My dissertation was a fishing expedition that described embryonic behavior and its neurophysiological mechanism. I was exploring uncharted waters and sought advice by observing the ultimate expert, the embryo. In this and related work, I discovered that prenatal movement is the product of seizure-like discharges in the spinal cord (not the brain), that the spinal discharges occurred spontaneously (not a response to sensory stimuli), that the function of  movement was to sculpt joints (not to shape postnatal behavior such walking), and to regulate the number of motorneurons. Remarkable! 

But decades later, this and similar work is largely unknown to developmental psychologists who have no category for it. The traditional psychological specialties of perception, learning, memory, motivation and the like, are not relevant during most of the prenatal period. The finding that embryos are profoundly unpsychological beings guided by unique developmental priorities and processes is not appreciated by theory-driven developmental psychologists. When the fishing expedition indicates that there is no appropriate spot in the scientific filing cabinet, it may be time to add another drawer. 

Years later and unrepentant, I embarked on a new fishing expedition, this time in pursuit of the human universal of laughter — what it is, when we do it, and what it means. In the spirit of my embryonic research, I wanted the expert to define my agenda—a laughing person. Explorations about research funding with administrators at a federal agency were unpromising. One linguist patiently explained that my project "had no obvious implications for any of the major theoretical issues in linguistics."  Another, a speech scientist, noted that "laughter isn't speech, and therefore had no relevance to my agency's mission." 

Ultimately, this atheoretical and largely descriptive work provided many surprises and counterintuitive findings. For example, laughter, like crying, is not consciously controlled, contrary to literature suggesting that we speak ha-ha as we would choose a word in speech. Most laughter is not a response to humor. Laughter and speech are controlled by different brain mechanisms, with speech dominating laughter. Contagious laughter is the product of neurologically programmed social behavior. Contrasts between chimpanzee and human laughter reveal why chimpanzees can't talk (inadequate breath control), and the evolutionary event necessary for the selection for human speech (bipedality).

Whether embryonic behavior or laughter, fishing expeditions guided me down the appropriate empirical path, provided unanticipated insights, and prevented flights of theoretical fancy. Contrary to lifelong advice, when planning a new research project, I always start by going fishing.

For most of my life I viewed any notion of the "soul" a fanciful religious invention. I agreed with the view of the late Nobel Laureate Francis Crick who in his book The Astonishing Hypothesis claimed "A modern neurobiologist sees no need for the religious concept of a soul to explain the behavior of humans and other animals." But is the idea of a soul really so crazy and beyond the limits of scientific reason? 

From the standpoint of neuroscience, it is easy to make the claim that Descartes is simply wrong about the separateness of brain and mind. The plain fact is that there is no scientific evidence that a self, an individual mind, or a soul could exist without a physical brain. However, there are persisting reasons why the self and the mind do not appear to be identical with, or entirely reducible to, the brain.

For example, in spite of the claims of Massachusetts physician Dr. Duncan MacDougall, who estimated through his experiments on dying humans that approximately 21 grams of matter — the presumed weight of the human soul — was lost upon death (The New York Times "Soul Has Weight, Physician Thinks" March 11, 1907), unlike the brain, the mind cannot be objectively observed, but only subjectively experienced. The subject that represents the "I" in the statement "I think therefore I am" cannot be directly observed, weighed, or measured. And the experiences of that self, its pains and pleasures, sights and sounds possess an objective reality only to the one who experiences them. In other words, as the philosopher John Searle puts it, the mind is "irreducibly first-person." 

On the other hand, although there are many perplexing properties about the brain, mind, and the self that remain to be scientifically explained — subjectivity among them — this does not mean that there must be an immaterial entity at work that explains these mysterious features. Nonetheless, I have come to believe that an individual consciousness represents an entity that is so personal and ontologically unique that it qualifies as something that we might as well call "a soul."

I am not suggesting that anything like a soul survives the death of the brain. Indeed, the link between the life of the brain and the life of the mind is irreducible, the one completely dependant upon the other. Indeed the danger of capturing the beauty and mystery of a personal consciousness and identity with the somewhat metaphorical designation "soul" is the tendency for the grandiose metaphor to obscure the actual accomplishments of the brain. The soul is not a "thing" independent of the living brain; it is part and parcel of it, its most remarkable feature, but nonetheless inextricably bound to its life and death.

I've begun to rethink the way we teach students to engage in scientific research. I was trained, as a chemist, to use the classic scientific method: Devise a testable hypothesis, and then design an experiment to see if the hypothesis is correct or not. And I was told that this method is equally valid for the social sciences. I've changed my mind that this is the best way to do science. I have three reasons for this change of mind.

First, and probably most importantly, I've learned that one often needs simply to sit and observe and learn about one's subject before even attempting to devise a testable hypothesis. What are the physical capacities of the subject? What is the social and ecological structure in which it lives? Does some anecdotal evidence suggest the form that the hypothesis should take? Few granting agencies are willing to provide support for this step, but it is critical to the scientific process, particularly for truly innovative research. Often, a proposal to gain observational experience is dismissed as being a "fishing expedition"…but how can one devise a workable hypothesis to test without first acquiring basic knowledge of the system, and how better to obtain such basic knowledge than to observe the system without any preconceived notions?

Second, I've learned that truly interesting questions really often can't be reduced to a simple testable hypothesis, at least not without being somewhat absurd. "Can a parrot label objects?" may be a testable hypothesis, but actually isn't very interesting…what is interesting, for example, is how that labeling compares to the behavior of a young child, exactly what type of training might enable such learning and what type of training is useless, how far can such labeling transfer across exemplars, and….Well, you get the picture…the exciting part is a series of interrelated questions that arise and expand almost indefinitely.

Third, I've learned that the scientific community's emphasis on hypothesis-based research leads too many scientists to devise experiments to prove, rather than test, their hypotheses. Many journal submissions lack any discussion of alternative competing hypotheses: Researchers don't seem to realize that collecting data that are consistent with their original hypothesis doesn't mean that it is unconditionally true. Alternatively, they buy into the fallacy that absence of evidence for something is always evidence of its absence.

I'm all for rigor in scientific research — but let's emphasize the gathering of knowledge rather than the proving of a point.

I grew up infused with the idea of unification. It came first from religion, from my Jewish background. God was all over, was all-powerful, and had a knack for interfering with human affairs, at least in the Old Testament. He then appeared to have decided to be a bit shyer, sending a Son instead, and only revealing Himself through visions and prophecies. Needless to say, when, as a teenager, I started to get interested in science, this vision of an all-pervading God, stories of floods, commandments and plagues, started to become very suspicious. I turned to physics, idolizing Einstein and his science; here was a Jew that saw further, that found a way of translating this old monotheistic tradition into the universal language of science.

As I started my research career, I had absolutely no doubt that I wanted to become a theoretical physicist working on particle physics and cosmology. Why the choice? Simple: it was the joining of the two worlds, of the very large and the very small, that offered the best hope for finding a unified theory of all Nature, that brought together matter and forces into one single magnificent formulation, the final Platonist triumph. This was what Einstein tried to do for the last three decades of his life, although in his days it was more a search for unifying only half of the forces of Nature, gravity and electromagnetism.

I wrote dozens of papers related to the subject of unification, even my Ph.D. dissertation was on the topic. I was fascinated by the modern approaches to the idea, supersymmetry, superstrings, a space with extra, hidden dimensions. A part of me still is. But then, a few years ago, something snapped. It probably was brought by a combination of factors, a deeper understanding of the historical and cultural processes that shape scientific ideas. I started to doubt unification, finding it to be the scientific equivalent of a monotheistic formulation of reality, a search for God revealed in equations. Of course, had we the slightest experimental evidence in favor of unification, of supersymmetry and superstrings, I'd be the first popping the champagne open. But it's been over twenty years, and all attempts so far have failed. Nothing in particle accelerators, nothing in cryogenic dark matter detectors, no magnetic monopoles, no proton decay, all tell-tale signs of unification predicted over the years. Even our wonderful Standard Model of particle physics, where we formulate the unification of electromagnetism and the weak nuclear interactions, is not really a true unification: the theory retains information from both interactions in the form of their strengths or, in more technical jargon, of their coupling constants. A true unification should have a single coupling constant, a single interaction.

All of my recent anti-unification convictions can crumble during the next few years, after our big new machine, the Large Hadron Collider, is turned on. Many colleagues hope that supersymmetry will finally show its face. Others even bet on possible signs of extra dimensions revealed. However, I have a feeling things won't turn out so nicely. The model of unification, which is so aesthetically appealing, may be simply this, an aesthetically appealing description of Nature, which, unfortunately, doesn't correspond to physical reality. Nature doesn't share our myths. The stakes are high indeed. But being a mild agnostic, I don't believe until there is evidence. And then, there is no need to believe any longer, which is precisely the beauty of science.

When I was very little the question was easy. I simply assumed the whole Bible was true, albeit in a mysterious, grown-up sort of way. But once I learned something of science, at school and then at university, that unquestioning belief slid away.

Mathematics was especially important here, and I remember how entranced I was when I first saw the power of axiomatic systems. Those were logical structures that were as beautiful as complex crystals —  but far, far clearer. If there was one inaccuracy at any point in the system, you could trace it, like a scarcely visible stretching crack through the whole crystal; you could see exactly how it had to undermine the validity of far distant parts as well. Since there are obvious factual inaccuracies in the Bible, as well as repugnant moral commands, then —  just as with any tight axiomatic system —  huge other parts of it had to be wrong, as well. In my mind that discredited it all.

What I've come to see more recently is that the Bible isn't monolithic in that way. It's built up in many, often quite distinct layers. For example, the book of Joshua describes a merciless killing of Jericho's inhabitants, after that city's walls were destroyed. But archaeology shows that when this was supposed to be happening, there was no large city with walls there to be destroyed. On the contrary, careful dating of artifacts, as well as translations from documents of the great empires in surrounding regions, shows that the bloodthirsty Joshua story was quite likely written by one particular group, centuries later, trying to give some validity to a particular royal line in 7th century BC Jerusalem, which wanted to show its rights to the entire country around it. Yet when that Joshua layer is stripped away, other layers in the Bible remain. They can stand, or be judged, on their own.

A few of those remaining layers have survived only because they became taken up by narrow power structures, concerned with aggrandizing themselves, in the style of Philip Pullman's excellent books. But others have survived across the millennia for different reasons. Some speak to the human condition with poetry of aching beauty. And others —  well, there's a further reason I began to doubt the inanity of everything I couldn't understand.

A child age three, however intelligent, and however much it squinches his or her fact tight in concentration, still won't be able to grasp notions that are easy for us, such as 'century', or 'henceforth', let alone greater subtleties which 20th century science has clarified, such as 'simultaneity' or 'causality'. True and important things exist, which young children can't comprehend. It seems odd to be sure that we, adult humans, existing at this one particular moment in evolution, have no such limits.

I realized that the world  isn't divided into science on the one hand, and nonsense or arbitrary biases on the other. And I wonder now what might be worth looking for, hidden there, fleetingly in-between.

I thought that it would change people. I thought it would allow us to build a new world through which we could model new behaviors, values, and relationships. In the 90's, I thought the experience of going online for the first time would change a person's consciousness as much as if they had dropped acid in the 60's.

I thought Amazon.com was a ridiculous idea, and that the Internet would shrug off business as easily as it did its original Defense Department minders.

For now, at least, it's turned out to be different.

Virtual worlds like Second Life have been reduced to market opportunities: advertisers from banks to soft drinks purchase space and create fake characters, while kids (and Chinese digital sweatshop laborers) earn "play money" in the game only to sell it to lazier players on eBay for real cash.

The businesspeople running Facebook and MySpace are rivaled only by the members of these online "communities" in their willingness to surrender their identities and ideals for a buck, a click-through, or a better market valuation.

The open source ethos has been reinterpreted through the lens of corporatism as "crowd sourcing" — meaning just another way to get people to do work for no compensation. And even "file-sharing" has been reduced to a frenzy of acquisition that has less to do with music than it does the ever-expanding hard drives of successive iPods.

Sadly, cyberspace has become just another place to do business. The question is no longer how browsing the Internet changes the way we look at the world; it's which browser we'll be using to buy and sell stuff in the same old world.

I used to think you could predict the future.  In "Profiles of the Future," Arthur C. Clarke made it seem so easy.  And so did all those other experts who confidently predicted the paperless office, the artificial intelligentsia who for decades predicted "human equivalence in ten years," the nanotechnology prophets who kept foreseeing major advances toward molecular manufacturing within fifteen years, and so on. 

Mostly, the predictions of science and technology types were wonderful: space colonies, flying cars in everyone's garage, the conquest (or even reversal) of aging.  (There were of course the doomsayers, too, such as the population-bomb theorists who said the world would run out of food by the turn of the century.) 

But at last, after watching all those forecasts not come true, and in fact become falsified in a crashing, breathtaking manner, I began to question the entire business of making predictions.  I mean, if even Nobel prizewinning scientists such as Ernest Rutherford, who gave us essentially the modern concept of the nuclear atom, could say, as he did in 1933, that "We cannot control atomic energy to an extent which would be of any value commercially, and I believe we are not likely ever to be able to do so," and be so spectacularly wrong about it, what hope was there for the rest of us? 

And then I finally decided that I knew the source of this incredible mismatch between confident forecast and actual result.  The universe is a complex system in which countless causal chains are acting and interacting independently and simultaneously (the ultimate nature of some of them unknown to science even today).  There are in fact so many causal sequences and forces at work, all of them running in parallel, and each of them often affecting the course of the others, that it is hopeless to try to specify in advance what's going to happen as they jointly work themselves out.  In the face of that complexity, it becomes difficult if not impossible to know with any assurance the future state of the system except in those comparatively few cases in which the system is governed by ironclad laws of nature such as those that allow us to predict the  phases of the moon, the tides, or the position of Jupiter in tomorrow night's sky.  Otherwise, forget it. 

Further, it's an illusion to think that supercomputer modeling is up to the task of truly reliable crystal-ball gazing.  It isn't.  Witness the epidemiologists who predicted that last year's influenza season would be severe (in fact it was mild); the professional hurricane-forecasters whose models told them that the last two hurricane seasons would be monsters (whereas instead they were wimps).  Certain systems in nature, it seems, are computationally irreducible phenomena, meaning that there is no way of knowing the outcome short of waiting for it to happen. 

Formerly, when I heard or read a prediction, I believed it.  Nowadays I just roll my eyes, shake my head, and turn the page.

Where once I would have striven to see Incan child sacrifice 'in their terms', I am increasingly committed to seeing it in ours. Where once I would have directed attention to understanding a past cosmology of equal validity to my own, I now feel the urgency to go beyond a culturally-attuned explanation and reveal cold sadism, deployed as a means of social control by a burgeoning imperial power.

In Cambridge at the end of the 70s, I began to be inculcated with the idea that understanding the internal logic and value system of a past culture was the best way to do archaeology and anthropology. The challenge was to achieve this through sensitivity to context, classification and symbolism. A pot was no longer just a pot, but a polyvalent signifier, with a range of case-sensitive meanings. A rubbish pit was no longer an unproblematic heap of trash, but a semiotic entity embodying concepts of contagion and purity, sacred and profane. A ritual killing was not to be judged bad, but as having validity within a different worldview.

Using such 'contextual' thinking, a lump of slag found in a 5000 BC female grave in Serbia was no longer seen as chance contaminant — bi-product garbage from making copper jewelry. Rather it was a kind of poetic statement bearing on the relationship between biological and cultural reproduction. Just as births in the Vin?a culture were attended by midwives who also delivered the warm but useless slab of afterbirth, so Vinca culture ore was heated in a clay furnace that gave birth to metal. From the furnace — known from many ethnographies to have projecting clay breasts and a graphically vulvic stoking opening — the smelters delivered technology's baby. With it came a warm but useless lump of slag. Thus the slag in a Vinca woman's grave, far from being accidental trash, hinted at a complex symbolism of gender, death and rebirth.

So far, so good: relativism worked as a way towards understanding that our industrial waste was not theirs, and their idea of how a woman should be appropriately buried not ours. But what happens when relativism says that our concepts of right and wrong, good and evil, kindness and cruelty, are inherently inapplicable? Relativism self-consciously divests itself of a series of anthropocentric and anachronistic skins — modern, white, western, male-focused, individualist, scientific (or 'scientistic') — to say that the recognition of such value-concepts is radically unstable, the 'objective' outsider opinion a worthless myth.

My colleague Andy Wilson and our team have recently examined the hair of sacrificed children found on some of the high peaks of the Andes. Contrary to historic chronicles that claim that being ritually killed to join the mountain gods was an honour that the Incan rulers accorded only to their own privileged offspring, diachronic isotopic analyses along the scalp hairs of victims indicate that it was peasant children, who, twelve months before death, were given the outward trappings of high status and a much improved diet to make them acceptable offerings. Thus we see past the self-serving accounts of those of the indigenous elite who survived on into Spanish rule. We now understand that the central command in Cuzco engineered the high-visibility sacrifice of children drawn from newly subject populations. And we can guess that this was a means to social control during the massive, 'shock & awe' style imperial expansion southwards into what became Argentina.

But the relativists demur from this understanding, and have painted us as culturally insensitive, ignorant scientists (the last label a clear pejorative). For them, our isotope work is informative only as it reveals 'the inner fantasy life of, mostly, Euro-American archaeologists, who can't possibly access the inner cognitive/cultural life of those Others.' The capital 'O' is significant. Here we have what the journalist Julie Burchill mordantly unpacked as 'the ever-estimable Other' — the albatross that post-Enlightenment and, more importantly, post-colonial scholarship must wear round its neck as a sign of penance.

We need relativism as an aid to understanding past cultural logic, but it does not free us from a duty to discriminate morally and to understand that there are regularities in the negatives of human behaviour as well as in its positives. In this case, it seeks to ignore what Victor Nell has described as 'the historical and cross-cultural stability of the uses of cruelty for punishment, amusement, and social control.' By denying the basis for a consistent underlying algebra of positive and negative, yet consistently claiming the necessary rightness of the internal cultural conduct of 'the Other', relativism steps away from logic into incoherence.

My academic experience, mainly at Columbia University from 1946-1978, instilled the following firm beliefs:

The role of the Professor, reflecting the mission of the University, is research and dissemination of the knowledge gained. However, the Professor has many citizenship obligations: to his community, State and Nation, to his University, to his field of research, e.g. physics, to his students. In the latter case, one must add to the content knowledge transferred, the moral and ethical concerns that science brings to society. So scientists have an obligation to communicate their knowledge, popularize, and whenever relevant, bring his knowledge to bear on the issues of the time. However, additionally, scientists play a large role in advisory boards and systems from the President's Advisory system all the way to local school boards and PTAs. I have always believed that the above menu more or less covered all the obligations and responsibilities of the scientist. His most sacred obligation is to continue to do science. Now I know that I was dead wrong.

Taking even a cursory stock of current events, I am driven to the ultimately wise advice of my Columbia mentor, I.I. Rabi, who, in our many corridor bull sessions, urged his students to run for public office and get elected. He insisted that to be an advisor (he was an advisor to Oppenheimer at Los Alamos, later to Eisenhower and to the AEC) was ultimately an exercise in futility and that the power belonged to those who are elected. Then, we thought the old man was bonkers. But today......

Just look at our national and international dilemmas: global climate change (U.S. booed in Bali); nuclear weapons (seventeen years after the end of the Cold War, the U.S. has over 7,000 nuclear weapons, many poised to instant flight. Who decided?); stem cell research (still hobbled by White House obstacles). Basic research and science education are rated several nations below "Lower Slobovenia", our national deficit will burden the nation for generations, a wave of religious fundamentalism, an endless war in Iraq and the growing security restrictions on our privacy and freedom (excused by an even more endless and mindless war on terrorism) seem to be paralyzing the Congress. We need to elect people who can think critically.

A Congress which is overwhelmingly dominated by lawyers and MBAs makes no sense in this 21st century in which almost all issues have a science and technology aspect. We need a national movement to seek out scientists and engineers who have demonstrated the required management and communication skills. And we need a strong consensus of mentors that the need for wisdom and knowledge in the Congress must have a huge priority.

As a student, I was influenced by Claude Lévi-Strauss and even more by Noam Chomsky. Both of them dared talk about "human nature" when the received view was that there was no such thing. In my own work, I argued for a naturalistic approach in the social sciences. I took for granted that human cognitive dispositions were shaped by biological evolution and more specifically by Darwinian selection. While I did occasionally toy with evolutionary speculations, I failed to see at the time how they could play more than a quite marginal role in the study of human psychology and culture.

Luckily, in 1987, I was asked by Jacques Mehler, the founder and editor of Cognition, to review a very long article intriguingly entitled "The logic of social exchange: Has natural selection shaped how humans reason?" In most experimental psychology articles the theoretical sections are short and relatively shallow. Here, on the other hand, the young author, Leda Cosmides, was arguing in an altogether novel way for an ambitious theoretical claim. The forms of cooperation unique to and characteristic of humans could only have evolved, she maintained, if there had also been, at a psychological level, the evolution of a mental mechanism tailored to understand and manage social exchanges and in particular to detect cheaters. Moreover, this mechanism could be investigated by means of standard reasoning experiments.

This is not the place to go into the details of the theoretical argument — which I found and still find remarkably insightful — or of the experimental evidence — which I have criticized in detail with experiments of my own as inadequate. Whatever its shortcoming, this was an extraordinarily stimulating paper, and I strongly recommended acceptance of a revised version. The article was published in 1989 and the controversies it stirred have not yet abated.

Reading the work of Leda Cosmides and of John Tooby, her collaborator (and husband), meeting them shortly after, and initiating a conversation with them that has never ceased made me change my mind. I had known that we could reflect on the mental capacities of our ancestors on the basis of what we know of our minds; I now understood that we can also draw fundamental insights about our present minds through reflecting on the environmental problems and opportunities that have exerted selective pressure on our Paleolithic ancestors.

Ever since, I have tried to contribute to the development of evolutionary psychology, to the surprise and dismay of some of my more standard-social-science friends and also of some evolutionary psychologists who see me more as a heretic than a genuine convert. True, I have no taste or talent for orthodoxy. Moreover, I find much of the work done so far under the label "evolutionary psychology" rather disappointing. Evolutionary psychology will succeed to the extent that it causes cognitive psychologists to rethink central aspects of human cognition in an evolutionary perspective, to the extent, that is, that psychology in general becomes evolutionary.

The human species is exceptional in its massive investment in cognition, and in forms of cognitive activity — language, higher-order thinking, abstraction — that are as unique to humans as echolocation is to bats. Yet more than half of all work done in evolutionary psychology today is about mate choice, a mental activity found in a great many species. There is nothing intrinsically wrong in studying mate choice, of course, and some of the work done in this area is outstanding.

However the promise of evolutionary psychology is first and foremost to help explain aspects of human psychology that are genuinely exceptional among earthly species and that in turn help explain the exceptional character of human culture and ecology. This is what has to be achieved to a much greater extent than has been the case so far if we want more skeptical cognitive and social scientists to change their minds too.

I have become convinced that it would be of fundamental importance to know what a good state of consciousness is. Are there forms of subjective experience which — in a strictly normative sense — are better than others? Or worse? What states of consciousness should be illegal? What states of consciousness do we want to foster and cultivate and integrate into our societies? What states of consciousness can we force upon animals — for instance, in consciousness research itself? What states of consciousness do we want to show our children? And what state of consciousness do we eventually die in ourselves?

2007 has seen the rise of an important new discipline: "neuroethics". This is not simply a new branch of applied ethics for neuroscience — it raises deeper issues about selfhood, society and the image of man.  Neuroscience is now quickly transformed into neurotechnology. I predict that parts of neurotechnology will turn into consciousness technology. In 2002, out-of-body experiences were, for the first time, induced with an electrode in the brain of an epileptic patient.  In 2007 we saw the first two studies, published in Science, demonstrating how the conscious self can be transposed to a location outside of the physical body as experienced, non-invasively and in healthy subjects. Cognitive enhancers are on the rise. The conscious experience of will has been experimentally constructed and manipulated in a number of ways. Acute episodes of depression can be caused by direct interventions in the brain, and they have also been successfully blocked in previously treatment-resistant patients. And so on.

Whenever we understand the specific neural dynamics underlying a specific form of conscious content, we can in principle delete, amplify or modulate this content in our minds. So shouldn’t we have a new ethics of consciousness — one that does not ask what a good actionis, but that goes directly to the heart of the matter, asks what we want to do with all this new knowledge and what the moral value ofstates of subjective experience is?

Here is where I have changed my mind. There are no moral facts. Moral sentences have no truth-values. The world itself is silent, it just doesn’t speak to us in normative affairs — nothing in the physical universe tells us what makes an action a good action or a specific brain-state a desirable one. Sure, we all would like to know what a good neurophenomenological configuration really is, and how we should optimize our conscious minds in the future. But it looks like, in a more rigorous and serious sense, there is just no ethical knowledge to be had. We are alone. And if that is true, all we have to go by are the contingent moral intuitions evolution has hard-wired into our emotional self-model. If we choose to simply go by what feels good, then our future is easy to predict: It will be primitive hedonism and organized religion.

Darwin is the man, and like so many biologists, I have benefited from his prescient insights, handed to us 150 years ago. The logic of adaptation has been a guiding engine of my research and my view of life. In fact, it has been difficult to view the world through any other filter. I can still recall with great vividness the day I arrived in Cambridge, in June 1992, a few months before starting my job as an assistant professor at Harvard. I was standing on a street corner, waiting for a bus to arrive, and noticed a group of pigeons on the sidewalk. There were several males displaying, head bobbing and cooing, attempting to seduce the females. The females, however, were not paying attention. They were all turned, in Prussian solider formation, out toward the street, looking at the middle of the intersection where traffic was whizzing by. There, in the intersection, was one male pigeon, displaying his heart out. Was this guy insane? Hadn’t he read the handbook of natural selection. Dude, it’s about survival. Get out of the street!!!

Further reflection provided the solution to this apparently mutant, male pigeon. The logic of adaptation requires us to ask about the costs and benefits of behavior, trying to understand what the fitness payoffs might be. Even for behaviors that appear absurdly deleterious, there is often a benefit lurking. In the case of our apparently suicidal male pigeon, there was a benefit, and it was lurking in the females’ voyeurism, their rubber necking. The females were oriented toward this male, as opposed to the conservative guys on the sidewalk, because he was playing with danger, showing off, proving that even in the face of heavy traffic, he could fly like a butterfly and sting like a bee, jabbing and jiving like the great Muhammed Ali.

The theory comes from the evolutionary biologist Amotz Zahavi who proposed that even costly behaviors that challenge survival can evolve if they have payoffs to genetic fitness; these payoffs arrive in the currency of more matings, and ultimately, more babies. Our male pigeon was showing off his handicap. He was advertising to the females that even in the face of potential costs from Hummers and Beamers and Buses, he was still walking the walk and talking the talk. The females were hooked, mesmerized by this extraordinarily macho male. Handicaps evolve because they are honest indicators of fitness. And Zahavi’s theory represents the intellectual descendent of Darwin’s original proposal.

I must admit, however, that in recent years, I have made less use of Darwin’s adaptive logic. It is not because I think that the adaptive program has failed, or that it can’t continue to account for a wide variety of human and animal behavior. But with respect to questions of human and animal mind, and especially some of the unique products of the human mind — language, morality, music, mathematics — I have, well, changed my mind about the power of Darwinian reasoning.

Let me be clear about the claim here. I am not rejecting Darwin’s emphasis on comparative approaches, that is, the use of phylogenetic or historical data. I still practice this approach, contrasting the abilities of humans and animals in the service of understanding what is uniquely human and what is shared. And I still think our cognitive prowess evolved, and that the human brain and mind can be studied in some of the same ways that we study other bits of anatomy and behavior. But where I have lost the faith, so to speak, is in the power of the adaptive program to explain or predict particular design features of human thought.

Although it is certainly reasonable to say that language, morality and music have design features that are adaptive, that would enhance reproduction and survival, evidence for such claims is sorely missing. Further, for those who wish to argue that the evidence comes from the complexity of the behavior itself, and the absurdly low odds of constructing such complexity by chance, these arguments just don’t cut it with respect to explaining or predicting the intricacies of language, morality, music or many other domains of knowledge.

In fact, I would say that although Darwin’s theory has been around, and readily available for the taking for 150 years, it has not advanced the fields of linguistics, ethics, or mathematics. This is not to say that it can’t advance these fields. But unlike the areas of economic decision making, mate choice, and social relationships, where the adaptive program has fundamentally transformed our understanding, the same can not be said for linguistics, ethics, and mathematics. What has transformed these disciplines is our growing understanding of mechanism, that is, how the mind represents the world, how physiological processes generate these representations, and how the child grows these systems of knowledge.

Bidding Darwin adieu is not easy. My old friend has served me well. And perhaps one day he will again. Until then, farewell.

When asked why all of her marriages failed, anthropologist Margaret Mead apparently replied, "I beg your pardon, I have had three marriages and none of them was a failure."  There are many people like Mead.  Some 90% of Americans marry by middle age.  And when I looked at United Nations data on 97 other societies, I found that more than 90% of men and women eventually wed in the vast majority of these cultures, too.  Moreover, most human beings around the world marry one person at a time: monogamy.  Yet, almost everywhere people have devised social or legal means to untie the knot.  And where they can divorce — and remarry — many do. 

So I had long suspected this human habit of "serial monogamy" had evolved for some biological purpose.  Planned obsolescence of the pairbond?  Perhaps the mythological "seven-year itch" evolved millions of years ago to enable a bonded pair to rear two children through infancy together.  If each departed after about seven years to seek "fresh features," as poet Lord Byron put it, both would have ostensibly reproduced themselves and both could breed again — creating more genetic variety in their young. 

So I began to cull divorce data on 58 societies collected since 1947 by the Statistical Office of the United Nations.  My mission: to prove that the "seven year itch" was a worldwide biological phenomenon associated in some way with rearing young.  

Not to be.  My intellectual transformation came while I was pouring over these divorce statistics in a rambling cottage, a shack really, on the Massachusetts coast one August morning.  I regularly got up around 5:30, went to a tiny desk that overlooked the deep woods, and poured over the pages I had Xeroxed from the United Nations Demographic Yearbooks.  But in country after country, and decade after decade, divorces tended to peak (the divorce mode) during and around the fourth year of marriage.  There were variations, of course.  Americans tended to divorce between the second and third year of marriage, for example.  Interestingly, this corresponds with the normal duration of intense, early stage, romantic love — often about 18 months to 3 years.  Indeed, in a 2007 Harris poll, 47% of American respondents said they would depart an unhappy marriage when the romance wore off, unless they had conceived a child.

Nevertheless, there was no denying it:  Among these hundreds of millions of people from vastly different cultures, three patterns kept emerging.  Divorces regularly peaked during and around the fourth year after wedding.  Divorces peaked among couples in their late twenties.  And the more children a couple had, the less likely they were to divorce: some 39% of worldwide divorces occurred among couples with no dependent children; 26% occurred among those with one child; 19% occurred among couples with two children; and 7% of divorces occurred among couples with three young. 

I was so disappointed.  I mulled about this endlessly.  My friend used to wave his hand over my face, saying, "Earth to Helen; earth to Helen."  Why do so many men and women divorce during and around the 4-year mark; at the height of their reproductive years; and often with a single child?  It seemed like such an unstable reproductive strategy.  Then suddenly I got that "ah-ha" moment:  Women in hunting and gathering societies breastfeed around the clock, eat a low-fat diet and get a lot of exercise — habits that tend to inhibit ovulation.  As a result, they regularly space their children about four years apart.  Thus, the modern duration of many marriages—about four years—conforms to the traditional period of human birth spacing, four years. 

Perhaps human parental bonds originally evolved to last only long enough to raise a single child through infancy, about four years, unless a second infant was conceived.  By age five, a youngster could be reared by mother and a host of relatives. Equally important, both parents could choose a new partner and bear more varied young.

My new theory fit nicely with data on other species.  Only about three percent of mammals form a pairbond to rear their young.  Take foxes.  The vixen's milk is low in fat and protein; she must feed her kits constantly; and she will starve unless the dog fox brings her food.  So foxes pair in February and rear their young together.  But when the kits leave the den in mid summer, the pairbond breaks up.  Among foxes, the partnership lasts only through the breeding season.  This pattern is common in birds.  Among the more than 8,000 avian species, some 90% form a pairbond to rear their young.  But most do not pair for life. A male and female robin, for example, form a bond in the early spring and rear one or more broods together.  But when the last of the fledgling fly away, the pairbond breaks up.  

Like pair-bonding in many other creatures, humans have probably inherited a tendency to love and love again—to create more genetic variety in our young.  We aren't puppets on a string of DNA, of course.  Today some 57% of American marriages last for life.  But deep in the human spirit is a restlessness in long relationships, born of a time long gone, as poet John Dryden put it, "when wild in wood the noble savage ran."

One of the big problems in physics — perhaps the biggest! — is figuring out how our two current best theories fit together. On the one hand we have the Standard Model, which tries to explain all the forces except gravity, and takes quantum mechanics into account.  On the other hand we have General Relativity, which tries to explain gravity, and does not take quantum mechanics into account. Both theories seem to be more or less on the right track — but until we somehow fit them together, or completely discard one or both, our picture of the world will be deeply schizophrenic.

It seems plausible that as a step in the right direction we should figure out a theory of gravity that takes quantum mechanics into account, but reduces to General Relativity when we ignore quantum effects (which should be small in many situations). This is what people mean by "quantum gravity" — the quest for such a theory.

The most popular approach to quantum gravity is string theory.  Despite decades of hard work by many very smart people, it's far from clear that this theory is successful. It's made no predictions that have been confirmed by experiment.  In fact, it's made few predictions that we have any hope of testing anytime soon!  Finding certain sorts of particles at the big new particle accelerator near Geneva would count as partial confirmation, but string theory says very little about the details of what we should expect. In fact, thanks to the vast "landscape" of string theory models that researchers are uncovering, it keeps getting harder to squeeze specific predictions out of this theory.

When I was a postdoc, back in the 1980s, I decided I wanted to work on quantum gravity. The appeal of this big puzzle seemed irresistible.  String theory was very popular back then, but I was skeptical of it.  I became excited when I learned of an alternative approach pioneered by Ashtekar, Rovelli and Smolin, called loop quantum gravity.

Loop quantum gravity was less ambitious than string theory. Instead of a "theory of everything", it only sought to be a theory of something: namely, a theory of quantum gravity.

So, I jumped aboard this train, and for about a decade I was very happy with the progress we were making. A beautiful picture emerged, in which spacetime resembles a random "foam" at very short distance scales, following the laws of quantum mechanics.

We can write down lots of theories of this general sort. However, we have never yet found one for which we can show that General Relativity emerges as a good approximation at large distance scales — the quantum soap suds approximating a smooth surface when viewed from afar, as it were.

I helped my colleagues Dan Christensen and Greg Egan do a lot of computer simulations to study this problem. Most of our results went completely against what everyone had expected.  But worse, the more work we did, the more I realized I didn't know what questions we should be asking!  It's hard to know what to compute to check that a quantum foam is doing its best to mimic General Relativity.

Around this time, string theorists took note of loop quantum gravity people and other critics — in part thanks to Peter Woit's blog, his bookNot Even Wrong, and Lee Smolin's book The Trouble with Physics.  String theorists weren't used to criticism like this.  A kind of "string-loop war" began.  There was a lot of pressure for physicists to take sides for one theory or the other. Tempers ran high.

Jaron Lanier put it this way: "One gets the impression that some physicists have gone for so long without any experimental data that might resolve the quantum-gravity debates that they are going a little crazy."  But even more depressing was that as this debate raged on, cosmologists were making wonderful discoveries left and right, getting precise data about dark energy, dark matter and inflation.  None of this data could resolve the string-loop war! Why?  Because neither of the contending theories could make predictions about the numbers the cosmologists were measuring! Both theories were too flexible.

I realized I didn't have enough confidence in either theory to engage in these heated debates.  I also realized that there were other questions to work on: questions where I could actually tell when I was on the right track, questions where researchers cooperate more and fight less.  So, I eventually decided to quit working on quantum gravity.

It was very painful to do this, since quantum gravity had been my holy grail for decades.  After you've convinced yourself that some problem is the one you want to spend your life working on, it's hard to change your mind.  But when I finally did, it was tremendously liberating.

I wouldn't urge anyone else to quit working on quantum gravity. Someday, someone is going to make real progress.  When this happens, I may even rejoin the subject.  But for now, I'm thinking about other things.  And, I'm making more real progress understanding the universe than I ever did before.

In the last few years I have changed my mind about nuclear power. I used to believe that expanding nuclear power was too risky. Now I believe that the risks of climate change are much greater than the risks of nuclear power. As a result we need to move urgently toward a new generation of nuclear reactors.  

What led to the change of view? First I came to believe that the likelihood of major climate related catastrophes was increasing rapidly and that they were likely to occur much sooner than the simple  linear models of the IPCC indicated. My analysis developed as a result of work we did for the defense and intelligence community on the national security implications of climate change. Many regions of the Earth are likely to experience an increasing frequency of extreme weather events. These catastrophic events include megastorms, super tornados, torrential rains and floods, extended droughts, ecosystem disruptions all added to steadily rising sea levels. It also became clear that human induced climate change is ever more at the causal center of the story.

Research by climatologists like William Ruddiman indicate that the climate is more sensitive to changes in human societies ranging from agricultural practices like forest clearing and  irrigated rice growing to major plagues to the use of fossil fuels. Human societies have often gone to war as a result of the ecological exhaustion of their local environments. So it becomes an issue of war and peace. Will Vietnam simply roll over and die when the Chinese dam what remains of the trickle of the Mekong as an extended drought develops at is source in the Tibetan highlands?

 Even allowing for much greater efficiency and a huge expansion of renewable energy, the real fuel of the future is coal, especially in the US, China and India. if all three go ahead with their current plans on building coal fired electric generating plants then that alone will over the next two decades double all the CO2 that human kind has put into the atmosphere since the industrial revolution began more than two hundred years ago. And the only meaningful alternative to coal is nuclear power. It is true that we can hope that our ability to capture the CO2 from coal burning and sequester it in various ways will grow, but it will take a decade or more before that technology reaches commercial maturity.

At the same time I also came to believe that risks of  nuclear power are less than we feared. That shift began with a trip to visit the proposed nuclear waste depository at Yucca Mountain in Nevada. A number ofEdge folk went including Stewart Brand, Kevin Kelly, Danny Hillis, and Pierre Omidyar. When it became clear that very long term storage of waste (e.g. 10,000 to 250,000 years) is a silly idea and not meaningfully realistic we began to question many of the assumptions about the future of nuclear power. The right answer to nuclear waste is temporary storage for perhaps decades and then recycling the fuel as much of the world already does, not sticking it underground for millennia. We will likely need the fuel we can extract from the waste.

There are emerging technologies for both nuclear power and waste reprocessing that will reduce safety risk, the amount of waste and most especially the risk of nuclear weapons proliferation as the new fuel cycle produces no plutonium, the offending substance of concern. And the economics are increasingly favorable as the French have demonstrated for decades. The average French citizen produces 70% less CO2 than the average American as a result. We have also learned that the long term consequences of the worst nuclear accident in history, Chernobyl were much less than feared.

So the conclusion is that the risks of climate change are far greater than the risks of nuclear power. Furthermore, human skill and knowledge in managing a nuclear system are only likely to grow with time. While the risks of climate change will grow as billions more people get rich and change the face of the planet with their demands for more stuff. Nuclear power is the only source of electricity that we can now see that is likely to enable the next three or four billion who want what we all have to get what they want without radically changing the climate of the Earth.

Most cosmologists would say the answer is "inflation," and, until recently, I would have been among them. But "facts have changed my mind" — and I now feel compelled to seek a new explanation that may or may not incorporate inflation. 

The idea always seemed incredibly simple. Inflation is a period of rapid accelerated expansion that can transform the chaos emerging from the big bang into the smooth, flat homogeny observed by astronomers. If one likens the conditions following the bang to a wrinkled and twisted sheet of perfectly elastic rubber, then inflation corresponds to stretching the sheet at faster-than-light speeds until no vestige of its initial state remains. The "inflationary energy" driving the accelerated expansion then decays into the matter and radiation seen today and the stretching slows to a modest pace that allows the matter to condense into atoms, molecules, dust, planets, stars and galaxies. 

I would describe this version as the "classical view" of inflation in two senses. First, this is the historic picture of inflation first introduced and now appearing in most popular descriptions. Second, this picture is founded on the laws of classical physics, assuming quantum physics plays a minor role. Unfortunately, this classical view is dead wrong. Quantum physics turns out to play an absolutely dominant role in shaping the inflationary universe. In fact, inflation amplifies the randomness inherent in quantum physics to produce an universe that is random and unpredictable. 

This realization has come slowly. Ironically, the role of quantum physics was believed to be a boon to the inflationary paradigm when it was first considered twenty-five years ago by several theorists, including myself. The classical picture of inflation could not be strictly true, we recognized, or else the universe would be so smooth after inflation that galaxies and other large-scale structures would never form. However, inflation ends through the quantum decay of inflationary energy into matter and radiation. The quantum decay is analogous to the decay of radioactive uranium, in which there is some mean rate of decay but inherent unpredictability as to when any particular uranium nucleus will decay. Long after most uranium nuclei have decayed, there remain some nuclei that have yet to fission.

Similarly, inflationary energy decays at slightly different times in different places, leading to spatial variations in the temperature and matter density after inflation ends. The "average" statistical pattern appears to agree beautifully with the pattern of microwave background radiation emanating from the earliest stages of the universe and to produce just the pattern of non-uniformities needed to explain the evolution and distribution of galaxies. The agreement between theoretical calculation and observations is a celebrated triumph of the inflationary picture. 

But is this really a triumph? Only if the classical view were correct. In the quantum view, it makes no sense to talk about an "average" pattern. The problem is that, as in the case of uranium nuclei, there always remain some regions of space in which the inflationary energy has not yet decayed into matter and radiation at all. Although one might have guessed the undecayed regions are rare, they expand so much faster than those that have decayed that they soon overtake the volume of the universe. The patches where inflationary energy has decayed and galaxies and stars have evolved become the oddity — rare pockets surrounded by space that continues to inflate away.

The process repeats itself over and over, with the number of pockets and the volume of surrounding space increasing from moment to moment. Due to random quantum fluctuations, pockets with all kinds of properties are produced — some flat, but some curved; some with variations in temperature and density like what we observe, but some not; some with forces and physical laws like those we experience, but some with different laws. The alarming result is that there are an infinite number of pockets of each type and, despite over a decade of attempts to avoid the situation, no mathematical way of deciding which is more probable has been shown to exist.

Curiously, this unpredictable "quantum view" of inflation has not yet found its way into the consciousness of many astronomers working in the field, let alone the greater scientific community or the public at large.

One often reads that recent measurements of the cosmic microwave background or the large-scale structure of the universe have verified a prediction of inflation. This invariably refers to a prediction based on the naïve classical view. But if the measurements ever come out differently, this could not rule out inflation. According to the quantum view, there are invariably pockets with matching properties.

And what of the theorists who have been developing the inflationary theory for the last twenty-five years? Some, like me, have been in denial, harboring the hope that a way can be found to tame the quantum effects and restore the classical view. Others have embraced the idea that cosmology may be inherently unpredictable, although this group is also vociferous in pointing how observations agree with the (classical) predictions of inflation.

Speaking for myself, it may have taken me longer to accept its quantum nature than it should have, but, now that facts have changed my mind, I cannot go back again. Inflation does not explain the structure of the universe. Perhaps some enhancement can explain why the classical view works so well, but then it will be that enhancement rather than inflation itself that explains the structure of the universe. Or maybe the answer lies beyond the big bang. Some of us are considering the possibility that the evolution of the universe is cyclic and that the structure was set by events that occurred before the big bang. One of the draws of this picture is that quantum physics does not play the same dominant role, and there is no escaping its predictions of the uniformity, flatness and structure of the universe.

The question presupposes a well defined "you", and an implied ability that is under "your" control to change your "mind". The "you" I now believe is distributed amongst others (family friends , in hierarchal structures,) i.e. suicide bombers, believe their sacrifice is for the other parts of their "you". The question carries with it an intention that I believe is out of one's control. My mind changed as a result of its interaction with its environment. Why? because it is a part of it.

Much of what I believed about human nature, and the nature of knowledge, has been upended by the Wikipedia. I knew that the human propensity for mischief among the young and bored — of which there were many online — would make an encyclopedia editable by anyone an impossibility. I also knew that even among the responsible contributors, the temptation to exaggerate and misremember what we think we know was inescapable, adding to the impossibility of a reliable text. I knew from my own 20-year experience online that you could not rely on what you read in a random posting, and believed that an aggregation of random contributions would be a total mess. Even unedited web pages created by experts failed to impress me, so an entire encyclopedia written by unedited amateurs, not to mention ignoramuses, seemed destined to be junk.

Everything I knew about the structure of information convinced me that knowledge would not spontaneously emerge from data, without a lot of energy and intelligence deliberately directed to transforming it. All the attempts at headless collective writing I had been involved with in the past only generated forgettable trash. Why would anything online be any different?

So when the first incarnation of the Wikipedia launched in 2000 (then called Nupedia) I gave it a look, and was not surprised that it never took off. There was a laborious process of top-down editing and re-writing that discouraged a would-be random contributor. When the back-office wiki created to facilitate the administration of the Nupedia text became the main event and anyone could edit as well as post an article, I expected even less from the effort, now re-named Wikipedia.

How wrong I was. The success of the Wikipedia keeps surpassing my expectations. Despite the flaws of human nature, it keeps getting better. Both the weakness and virtues of individuals are transformed into common wealth, with a minimum of rules and elites. It turns out that with the right tools it is easier to restore damage text (the revert function on Wikipedia) than to create damage text (vandalism) in the first place, and so the good enough article prospers and continues. With the right tools, it turns out the collaborative community can outpace the same number of ambitious individuals competing.

It has always been clear that collectives amplify power — that is what cities and civilizations are — but what's been the big surprise for me is how minimal the tools and oversight are needed. The bureaucracy of Wikipedia is relatively so small as to be invisible. It's the Wiki's embedded code-based governance, versus manager-based governance that is the real news. Yet the greatest surprise brought by the Wikipedia is that we still don't know how far this power can go. We haven't seen the limits of wiki-ized intelligence. Can it make textbooks, music and movies? What about law and political governance?

Before we say, "Impossible!" I say, let's see. I know all the reasons why law can never be written by know-nothing amateurs. But having already changed my mind once on this, I am slow to jump to conclusions again. The Wikipedia is impossible, but here it is. It is one of those things impossible in theory, but possible in practice. Once you confront the fact that it works, you have to shift your expectation of what else that is impossible in theory might work in practice.

I am not the only one who has had his mind changed about this. The reality of a working Wikipedia has made a type of communitarian socialism not only thinkable, but desirable. Along with other tools such as open-source software and open-source everything, this communtarian bias runs deep in the online world.

In other words it runs deep in this young next generation. It may take several decades for this shifting world perspective to show its full colors.  When you grow up knowing rather than admitting that such a thing as the Wikipedia works; when it is obvious to you that open source software is better; when you are certain that sharing your photos and other data yields more than safeguarding them — then these assumptions will become a platform for a yet more radical embrace of the commonwealth. I hate to say it but there is a new type of communism or socialism loose in the world, although neither of these outdated and tinged terms can accurately capture what is new about it.

The Wikipedia has changed my mind, a fairly steady individualist, and lead me toward this new social sphere. I am now much more interested in both the new power of the collective, and the new obligations stemming from individuals toward the collective. In addition to expanding civil rights, I want to expand civil duties. I am convinced that the full impact of the Wikipedia is still subterranean, and that its mind-changing power is working subconsciously on the global millennial generation, providing them with an existence proof of a beneficial hive mind, and an appreciation for believing in the impossible.

That's what it's done for me.

Our science, including mine, treats living systems as mechanisms at multiple levels of abstraction.  As we talk about how one bio-molecule docks with another our explanations are purely mechanistic and our science never invokes "and then the soul intercedes and gets them to link up". The underlying assumption of molecular biologists is that their level of mechanistic explanation is ultimately adequate for high level mechanistic descriptions such as physiology and neuroscience to build on as a foundation.

Those of us who are computer scientists by training, and I'm afraid many collaterally damaged scientists of other stripes, tend to use computation as the mechanistic level of explanation for how living systems behave and "think".  I originally gleefully embraced the computational metaphor

If we look back over recent centuries we will see the brain described as a hydrodynamic machine, clockwork, and as a steam engine.  When I was a child in the 1950's I read that the human brain was a telephone switching network.  Later it became a digital computer, and then a massively parallel digital computer.  A few years ago someone put up their hand after a talk I had given at the University of Utah and asked a question I had been waiting for for a couple of years: "Isn't the human brain just like the world wide web?".  The brain always seems to be one of the most advanced technologies that we humans currently have.

The metaphors we have used in the past for the brain have not stood the test of time.  I doubt that our current metaphor of the brain as a network of computers doing computations is going to stand for all eternity either.

Note that I do not doubt that there are mechanistic explanations for how we think, and I certainly proceed with my work of trying to build intelligent robots using computation as a primary tool for expressing mechanisms within those robots.

But I have relatively recently come to question computation as the ultimate metaphor to be used in both the understanding of living systems and as the only important design tool for engineering intelligent artifacts.

Some of my colleagues have managed to recast Pluto's orbital behavior as the body itself carrying out computations on forces that apply to it.  I think we are perhaps better off using Newtonian mechanics (with a little Einstein thrown in) to understand and predict the orbits of planets and others.  It is so much simpler.

Likewise we can think about spike trains as codes and worry about neural coding.  We can think about human memory as data storage and retrieval.  And we can think about walking over rough terrain as computing the optimal place to put down each of our feet.  But I suspect that somewhere down the line we are going to come up with better, less computational metaphors.  The entities we use for metaphors may be more complex but the useful ones will lead to simpler explanations.

Just as the notion of computation is only a short step beyond discrete mathematics, but opens up vast new territories of questions and technologies, these new metaphors might well be just a few steps beyond where we are now in understanding organizational dynamics, but they may have rich and far reaching implications in our abilities to understand the natural world and to engineer new creations.

When I first saw the possibility (some 30 years ago) of grounding a science of human self-deception in evolutionary logic (based on its value in furthering deception of others), I imagined joining evolutionary theory with animal behavior and with those parts of psychology worth preserving. The latter I regarded as a formidable hurdle since so much of psychology (depth and social) appeared to be pure crap, or more generously put, without any foundation in reality or logic.

Now after a couple of years of intensive study of the subject, I am surprised at the number of areas of biology that are important, if not key, to the subject yet are relatively undeveloped by biologists. I am also surprised that many of the important new findings in this regard have been made by psychologists and not biologists.

It was always obvious that when neurophysiology actually became a science (which it did when it learned to measure on-going mental activity) it would be relevant to deceit and self-deception and this is becoming more apparent every day. Also, endocrinology could scarcely be irrelevant and Richard Wrangham has recently argued for an intimate connection between testosterone and self-deception in men but the connections must be much deeper still. The proper way to conceptualize the endocrine system (as David Haig has pointed out to me) is as a series of signals with varying half-lives which give relevant information to organs downstream and many such signals may be relevant to deceit and self-deception and to selves-deception, as defined below.

One thing I never imagined was that the immune system would be a vital component of any science of self-deception, yet two lines of work within psychology make this clear. Richard Davidson and co-workers have shown that relatively positive, up, approach-seeking people are more likely to be left-brain activated (as measured by EEG) and show stronger immune responses to a novel challenge (flu vaccine) than are avoidance, negative emotion (depression, anxiety) right-brained people.  At the same time, James Pennebaker and colleagues have shown that the very act of repressing information from consciousness lowers immune function while sharing information with others (or even a diary) has the opposite effect. Why should the immune system be so important and why should it react in this way?

A key variable in my mind is that the immune system is an extremely expensive one—we produce a grapefruit-sized set of tissue every two weeks—and we can thus borrow against it, apparently in part for brain function. But this immediately raises the larger question of how much we can borrow against any given system—yes fat for energy, bone and teeth when necessary (as for a child in utero), muscle when not used and so on—but with what effects? Why immune function and repression?

While genetics is, in principle, important to all of biology, I thought it would be irrelevant to the study of self-deception until way into the distant future. Yet the 1980s produced the striking discovery that the maternal half of our genome could act against the paternal, and vice-versa, discoveries beautifully exploited in the 90’s and 00’s by David Haig to produce a range of expected (and demonstrated) internal conflicts which must inevitably interact with self-deception directed toward others. Put differently, internal genetic conflict leads to a quite novel possibility: selves-deception, equally powerful maternal and paternal halves selected to deceive each other (with unknown effects on deception of others).

And consider one of the great mysteries of mental biology. The human brain consumes about 20% of resting metabolic rate come rain or shine, whether depressed or happy, asleep or awake. Why? And why is the brain so quick to die when deprived of this energy? What is the cellular basis for all of this? How exactly does borrowing from other systems, such as immune, interact with this basic metabolic cost? Biologists have been very slow to see the larger picture and to see that fundamental discoveries within psychobiology require a deeper understanding of many fundamental biological processes, especially the logic of energy borrowed from various sources.

Finally, let me express a surprise about psychology. It has led the way in most of the areas mentioned, e.g. immune effects, neurophysiology, brain metabolism. Also, while classical depth psychology (Freud and sundries) can safely be thrown overboard almost in its entirety, social psychology has produced some very clever and hopeful methods, as well as a body of secure results on biased human mentation, from perception, to organization of data, to analysis, to further propagation. Daniel Gilbert gives a well-appreciated lecture in which he likens the human mind to a bad scientist, everything from biased exposure to data and biased analysis of information to outright forgery. Hidden here is a deeper point. Science progresses precisely because it has a series of anti-deceit-and-self-deception devices built into it, from full description of experiments permitting exact replication, to explicit statement of theory permitting precise counter-arguments, to the preference for exploring alternative working hypothesis, to a statistical apparatus able to weed out the effects of chance, and so on.

The year 2007 marked three memorable events in climate science:  Release of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4); a decade of drought in the American West and the arrival of severe drought in the American Southeast; and the disappearance of nearly half of the polar sea-ice floating over the Arctic Ocean. The IPCC report (a three-volume, three-thousand page synthesis of current scientific knowledge written for policymakers) and the American droughts merely hardened my conviction that anthropogenic climate warming is real and just getting going — a view shared, in the case of the IPCC, a few weeks ago by the Nobel Foundation. The sea-ice collapse, however, changed my mind that it will be decades before we see the real impacts of the warming. I now believe they will happen much sooner.

Let's put the 2007 sea-ice year into context. In the 1970's, when NASA first began mapping sea ice from microwave satellites, its annual minimum extent (in September, at summer's end) hovered close to 8 million square kilometers, about the area of the conterminous United States minus Ohio. In September 2007 it dropped abruptly to 4.3 million square kilometers, the area of the conterminous United State minus Ohio and all the other twenty-four states east of the Mississippi, as well as North Dakota, Minnesota, Missouri, Arkansas, Louisiana, and Iowa. Canada's Northwest Passage was freed of ice for the first time in human memory. From Bering Strait where the U.S. and Russia brush lips, open blue water stretched almost to the North Pole.

What makes the 2007 sea-ice collapse so unnerving is that it happened too soon.  The ensemble averages of our most sophisticated climate model predictions, put forth in the IPCC AR4 report and various other model intercomparison studies, don't predict a downwards lurch of that magnitude for another fifty years. Even the aggressive models -the National Center for Atmospheric Research (NCAR) CCSM3 and the Centre National de Recherches Meteorologiques (CNRM) CM3 simulations, for example — must whittle ice until 2035 or later before the 2007 conditions can be replicated.  Put simply, the models are too slow to match reality. Geophysicists, accustomed to non-linearities and hard to impress after a decade of 'unprecedented' events, are stunned by the totter:  Apparently, the climate system can move even faster than we thought.  This has decidedly recalibrated scientist's attitudes — including my own — to the possibility that even the direst IPCC scenario predictions for the end of this century — 10 to 24 inch higher global sea levels, for example — may be prudish.

What does all this say to us about the future? The first is that rapid climate change — a nonlinearity that occurs when a climate forcing reaches a threshold beyond which little additional forcing is needed to trigger a large impact — is a distinct threat not well captured in our current generation of computer models. This situation will doubtless improve — as the underlying physics of the 2007 ice event and others such as the American Southeast drought are dissected, understood, and codified — but in the meantime, policymakers must work from the IPCC blueprint which seems almost staid after the events of this summer and fall.  The second is that it now seems probable that the northern hemisphere will lose its ice lid far sooner than we ever thought possible.  Over the past three years experts have shifted from 2050, to 2035, to 2013 as plausible dates for an ice-free Arctic Ocean — estimates at first guided by models then revised by reality.

The broader significance of vanishing sea ice extends far beyond suffering polar bears, new shipping routes, or even development of vast Arctic energy reserves. It is absolutely unequivocal that the disappearance of summer sea ice — regardless of exactly which year it arrives — will profoundly alter the northern hemisphere climate, particularly through amplified winter warming of at least twice the global average rate. Its further impacts on the world's precipitation and pressure systems are under study but are likely significant. Effects both positive and negative, from reduced heating oil consumption to outbreaks of fire and disease, will propagate far southward into the United States, Canada, Russia and Scandinavia. Scientists have expected such things in eventuality — but in 2007 we learned they may already be upon us.

In an interview with the New York Times, shortly before he died, Francis Crick told a reporter, "the view of ourselves as [ensouled] 'persons' is just as erroneous as the view that the Sun goes around the Earth. This sort of language will disappear in a few hundred years. In the fullness of time, educated people will believe there is no soul independent of the body, and hence no life after death."

Like the vast majority of academic scientists and philosophers alive today, I accept Crick's philosophical assertion — that when your body dies, you cease to exist — without any reservations. I also used to agree with Crick's psychosocial prognosis — that modern education would inevitably give rise to a populace that rejected the idea of a supernatural soul. But on this point, I have changed my mind.

Underlying Crick's psychosocial claim is a common assumption: the minds of all intelligent people must operate according to the same universal principles of human nature. Of course, anyone who makes this assumption will naturally believe that their own mind-type is the universal one. In the case of Crick and most other molecular biologists, the assumed universal mind-type is highly receptive to the persuasive power of pure logic and rational analysis.

Once upon a time, my own worldview was similarly informed. I was convinced that scientific facts and rational argument alone could win the day with people who were sufficiently intelligent and educated. To my mind, the rejection of rational thought by such people was a sign of disingenuousness to serve political or ideological goals.

My mind began to change one evening in November 2003. I had given a lecture at small liberal arts college along with a member of The President's Council on Bioethics, whose views on human embryo research are diametrically opposed to my own. Surrounded by students at the wine and cheese reception that followed our lectures, the two of us began an informal debate about the true meaning and significance of changes in gene expression and DNA methylation during embryonic development. Six hours later, long after the last student had crept off to sleep, it was 4:00 am, and we were both still convinced that with just one more round of debate, we'd get the other to capitulate. It didn't happen.

Since this experience, I have purposely engaged other well-educated defenders of the irrational, as well as numerous students at my university, in spontaneous one-on-one debates about a host of contentious biological subjects including evolution, organic farming, homeopathy, cloned animals, "chemicals" in our food, and genetic engineering. Much to my chagrin, even after politics, ideology, economics, and other cultural issues have been put aside, there is often a refusal to accept scientific implications of rational argumentation.

While its mode of expression may change over cultures and time, irrationality and mysticism seem to be an integral part of normal human nature, even among highly educated people. No matter what scientific and technological advances are made in the future, I now doubt that supernatural beliefs will ever be eradicated from the human species.

When I was in graduate school, in the early 1990s, I learned two important things: that the human capacity for language was innate, and that the machinery that allowed human beings to learn language was "special", in the sense of being separate from the rest of the human mind.

Both ideas sounded great at the time. But (as far as I can tell know) only one of them turns out to be true.

I still think that I was right to believe in "innateness", the idea that the human mind, arrives, fresh from the factory, with a considerable amount of elaborate machinery. When a human embryo emerges from the womb, it has almost all the neurons it will ever have. All of the basic neural structures are already in place, and most or all of the basic neural pathways are established. There is, to be sure, lots of learning yet to come — an infant's brain is more rough draft than final product — but anybody who still imagines the infant human mind to be little more than an empty sponge isn't in touch with the realities of modern genetics and neuroscience. Almost half our genome is dedicated to the development of brain function, and those ten or fifteen thousand brain-related genes choreograph an enormous amount of biological sophistication.  Chomsky (whose classes I sat in on while in graduate school) was absolutely right to be insisting, for all these years, that language has its origins in the built-in structure of the mind.

But now I believe that I was wrong to accept the idea that language was separate from the rest of the human mind. It's always been clear that we can talk about what we think about, but when I was in graduate school it was popular to talk about language as being acquired by a separate "module" or "instinct" from the rest of cognition, by what Chomsky called a  "Language Acquisition Device" (or LAD). Its mission in life was to acquire language, and nothing else. 

In keeping with idea of language as product of specialized in-born mechanism, we noted how quickly how human toddlers acquired language, and how determined they were to do so; all normal human children acquire language, not just a select few raised in privileged environments, and they manage to do so rapidly, learning most of what they need to know in the first few years of life.  (The average adult, in contrast, often gives up around the time they have to face their fourth list of irregular verbs.)  Combine that with the fact that some children with normal intelligence couldn't learn language and that others with normal language lacked normal cognitive function, and I was convinced. Humans acquired language because they had a built-in module that was uniquely dedicated to that function.

Or so I thought then. By the late 1990s, I started looking beyond the walls of my own field (developmental psycholinguistics) and out towards a whole host of other fields, including genetics, neuroscience, and evolutionary biology.

The idea that most impressed me — and did the most to shake me of the belief that language was separate from the rest of the mind — goes back to Darwin. Not "survival of the fittest" (a phrase actually coined by Herbert Spencer) but his notion, now amply confirmed at the molecular level, that all biology is the product of what he called "descent with modification". Every species, and every biological system evolves through a combination of inheritance (descent) and change (modification). Nothing, no matter how original it may appear, emerges from scratch.

Language, I ultimately realized, must be no different: it emerged quickly, in the space of a few hundred thousand years, and with comparatively little genetic change. It suddenly dawned on me that the striking fact that our genomes overlap almost 99% with those of chimpanzees must be telling something: language couldn't possibly have started from scratch. There isn't enough room in the genome, or in our evolutionary history, for it to be plausible that language is completely separate from what came before.

Instead, I have now come to believe, language must be, largely, a recombination of spare parts, a kind of jury-rigged kluge built largely out of cognitive machinery that evolved for other purposes, long before there was such a thing as language. If there's something special about language, it is not the parts from which it is composed, but the way in which they are put together.

Neuorimaging studies seem to bear this out. Whereas we once imagined language to be produced and comprehended almost entirely by two purpose-built regions — Broca's area and Wernicke's area, we now see that many other parts of the brain are involved (e.g. the cerebellum and basal ganglia) and that the classic language areas (i.e. Broca's and Wernicke's) participate in other aspects of mental life (e.g., music and motor control) and have counterparts in other apes.

At the narrowest level, this means that psycholinguists and cognitive neuroscientists need to rethink their theories about what language is. But if there is a broader lesson, it is this: although we humans in many ways differ radically from any other species, our greatest gifts are built upon a genomic bedrock that we share with the many other apes that walk the earth.

I have a collection of web pages on the sustainability of material progress that treats many problems that have been proposed as possible stoppers. I get email about the pages, both unfavorable and favorable, mostly the latter.

I had believed that the email would concern specific problems or would raise new ones, e.g. "What about erosion of agricultural land?"

There's some of that, but overwhelmingly the email, both pro and con, concerns my attitude,  not my (alleged) facts. "How can you be so blithely cornucopian when everybody knows ..." or "I'm glad someone has the courage to take on all those doomsters."

It seems, to my surprise, that people's attitude that the future stems at least as much from personality as from opinions about facts. People look for facts to support their attitudes — which have earlier antecedents.

I have changed my mind about my body. I used to think of it as a kind of hardware on which my mental and behavioral software was running. Now, I primarily think of my body as software. 

My body is not like a typical material object, a stable thing.  It is more like a flame, a river or an eddie. Matter is flowing through it all the time. The constituents are being replaced over and over again.

A chair or a table is stable because the atoms stay where they are. The stability of a river stems from the constant flow of water through it.

98 percent of the atoms in the body are replaced every year. 98 percent! Water molecules stays in your body for two weeks (and for an even shorter time in a hot climate), the atoms in your bones stays there for a few months. Some atoms stay for years. But almost not one single atom stay with you in your body from cradle to grave.

What is constant in you is not material. An average person takes in 1.5 ton of matter every year as food, drinks and oxygen. All this matter has to learn to be you. Every year. New atoms will have to learn to remember your childhood.

These numbers has been known for half a century or more, mostly from studies of radioactive isotopes. Physicist Richard Feynman said in 1955: "Last week's potatoes! They now can remember what was going on in your mind a year ago."

But why is this simple insight not on the all-time Top 10 list of important discoveries? Perhaps because it tastes a little like spiritualism and idealism? Only the ghosts are for real? Wandering souls? 

But digital media now makes it possible to think of all this in a simple way. The music I danced to as a teenager has been moved from vinyl-LPs to magnetic audio tapes to CDs to Pods and whatnot. The physical representation can change and is not important — as long as it is there. The music can jump from medium to medium, but it is lost if it does not have a representation. This physics of information was sorted out by Rolf Landauer in the 1960'ies. Likewise, out memories can move from potato-atoms to burger-atoms to banana-atoms. But the moment they are on their own, they are lost.

We reincarnate ourselves all the time. We constantly give our personality new flesh. I keep my mental life alive by making it jump from atom to atom. A constant flow. Never the same atoms, always the same river. No flow, no river. No flow, no me.

This is what I call permanent reincarnation: Software replacing its hardware all the time. Atoms replacing atoms all the time. Life. This is very different from religious reincarnation with souls jumping from body to body (and souls sitting out there waiting for a body to take home in).

There has to be material continuity for permanent reincarnation to be possible. The software is what is preserved, but it cannot live on its own. It has to jump from molecule to molecule, always in carnation.

I have changed my mind about the stability of my body: It keeps changing all the time. Or I could not stay the same.

How is it that insects manage to get by on many fewer neurons than we have? A fly brain has a few hundred thousand neurons, compared to the few hundred billion in our brains, a million times more neurons. Flies are quite successful in their niche. They can see, find food, mate, and create the next generation of flies. The traditional view is that unique neurons evolved in the brain of the fly to perform specific tasks, in contrast to the mammalian strategy of creating many more neurons of the same type, working together in a collective fashion. This view was bolstered when it became possible to record from single cortical neurons, which responded to sensory stimuli with highly variable spike trains from trial to trial. Reliability could be achieved only by averaging the responses of many neurons.

Theoretical analysis of neural signals in large networks assumed statistical randomness in the responses of neurons. These theories used the average firing rates of neurons as the primary statistical variable. Individual spikes and the times when they occurred were not relevant in these theories. In contrast, the timing of single spikes in flies has been shown to carry specific information about sensory stimuli important for guiding the behavior of flies, and in mammals the timing of spikes in the peripheral auditory system carried information about the spatial locations of sound sources. However, cortical neurons did not seem to care about the timing of spikes.

I have changed my mind about cortical neurons and now think that they are far more capable than we ever imagined. Two important experimental results pointed me in this direction. First, if you repeatedly inject the same fluctuating current into a neuron in a cortical slice, to mimic the inputs that occur in an intact piece of tissue, the spike times are highly reproducible from trial to trial. This shows that cortical neurons are capable of initiating spikes with millisecond precision.  Second, if you arrange for a single synapse to be stimulated a few milliseconds just before or just after a spike in the neuron, the synaptic strength will increase or decrease, respectively. This tells us that the machinery in the cortex is every bit as capable as a fly brain, but what is it being used for?

The cerebral cortex is constantly being bombarded by sensory inputs and has to sort though the myriad of signals for those that are the most important and to respond selectively to them. The cortex also needs to organize the signals being generated internally, in the absence of sensory inputs. The hypothesis that I have been pursuing over the last decade is that spike timing in cortical neurons is used internally as a way of controlling the flow of communication between neurons. This is a different from the traditional view that spike times code sensory information, as occurs in the periphery. Rather, spike timing and the synchronous firing of large numbers of cortical neurons may be used to enhance the salience of sensory inputs, as occurs during focal attention, and to decide what information is worth saving for future use. According to this view, the firing rates of neurons are used as an internal representation of the world but the timing of spikes is used to regulate the communication of signals between cortical areas.

The way that neuroscientists perform experiments is biased by their theoretical views. If cortical neurons use rate coding you only need to record, and report, their average firing rates. But to find out if spike timing is important new experiments need to be designed and new types of analysis need to be performed on the data. Neuroscientists have begun to pursue these new experiments and we should know before too long where they will lead us.

I was born without the neural cluster that makes boys find pleasure in moving balls and pucks around through space, and in talking endlessly about men who get paid to do such things. I always knew I could never join a fraternity or the military because I wouldn't be able to fake the sports talk. By the time I became a professor I had developed the contempt that I think is widespread in academe for any institution that brings young men together to do groupish things. Primitive tribalism, I thought. Initiation rites, alcohol, sports, sexism, and baseball caps turn decent boys into knuckleheads. I'd have gladly voted to ban fraternities, ROTC, and most sports teams from my university.

But not anymore. Three books convinced me that I had misunderstood such institutions because I had too individualistic a view of human nature. The first book was David Sloan Wilson's Darwin's Cathedral, which argued that human beings were shaped by natural selection operating simultaneously at multiple levels, including the group level. Humans went through a major transition in evolution when we developed religiously inclined minds and religious institutions that activated those minds, binding people into groups capable of extraordinary cooperation without kinship. 

The second book was William McNeill's Keeping Together in Time, about the historical prevalence and cultural importance of synchronized dance, marching, and other forms of movement. McNeill argued that such "muscular bonding" was an evolutionary innovation, an "indefinitely expansible basis for social cohesion among any and every group that keeps together in time." The third book was Barbara Ehrenreich'sDancing in the Streets, which made the same argument as McNeill but with much more attention to recent history, and to the concept ofcommunitas or group love. Most traditional societies had group dance rituals that functioned to soften structure and hierarchy and to increase trust, love, and cohesion. Westerners too have a need for communitas, Ehrenreich argues, but our society makes it hard to satisfy it, and our social scientists have little to say about it.

These three books gave me a new outlook on human nature. I began to see us not just as chimpanzees with symbolic lives but also as bees without hives. When we made the transition over the last 200 years from tight communities (Gemeinschaft) to free and mobile societies (Gesellschaft), we escaped from bonds that were sometimes oppressive, yes, but into a world so free that it left many of us gasping for connection, purpose, and meaning. I began to think about the many ways that people, particularly young people, have found to combat this isolation. Rave parties and the Burning Man festival are spectacular examples of new ways to satisfy the ancient longing for communitas. But suddenly sports teams, fraternities, and even the military made a lot more sense.

I now believe that such groups do great things for their members, and that they often create social capital and other benefits that spread beyond their borders. The strong school spirit and alumni loyalty we all benefit from at the University of Virginia would drop sharply if fraternities and major sports were eliminated. If my son grows up to be a sports playing fraternity brother, a part of me may still be disappointed. But I'll give him my blessing, along with three great books to read.

The hottest topic in neuroscience today is brain plasticity. This catchphrase refers to the fact that various types of experience can significantly modify key attributes of the brain. This field began decades ago by focusing on how different aspects of the developing brain could be impacted by early rearing conditions.  

More recently, the field of brain plasticity has shifted to studies demonstrating a remarkable degree of change in the connections and functional properties of mature and even aged brains. Thousands of published papers have now appeared on this topic, many by reputable scientists, and this has lead to a host of books, programs and even commercial enterprises touting the malleability of the brain with “proper” training. One is practically made to feel guilty for not taking advantage of this thriving store of information to improve one’s own brain or those of one’s children and grandchildren. 

My field of research is developmental neurobiology and I used to be a proponent of the potential benefits documented by brain plasticity studies. I am still of the opinion that brain plasticity is a real phenomenon, one that deserves further study and one that could be utilized to better human welfare. But my careful reading of this literature has tempered my initial enthusiasm.

For one thing, those selling a commercial product are making many of the major claims for the benefits of brain exercise regimes. It is also the case that my experiences outside the laboratory have caused me to question the limitless potential of brain plasticity advocated by some devotees.

Point in fact: Recently I had the chance to meet someone I had not seen since childhood. The person had changed physically beyond all recognition, as might be expected.  Yet after spending some time with this individual, his personality traits of long ago became apparent, including a rather peculiar laugh I remember from grade school.

Point of fact: a close colleague had a near fatal car accident, one that caused him to be in a coma for many days and in intensive care for weeks thereafter. Shortly after returning from his ordeal, this A-type personality changed into a seemingly mellow and serene person. But in less than two months, even before the physical scars of his accident had healed, he was back to his old driven self. 

For a working scientist to invoke anecdotal experience to question a scientific field of endeavor is akin to heresy. But it seems to me that it is foolish to simply ignore what one has learned from a lifetime of experiences. The older I get the more my personal interactions convince me that a person’s core remains remarkably stable in spite of huge experiential variations. With all the recent emphasis on brain plasticity, there has been virtually no attempt to explain the stability of the individual’s core attributes, values and beliefs. 

Here is a real puzzle to ponder: Every cell in your body, including all 100 billion neurons in your brain is in a constant process of breakdown and renewal. Your brain is different than the one you had a year or even a month ago, even without special brain exercises. So how is the constancy of one’s persona maintained?   The answer to that question offers a far greater challenge to our understanding of the brain than the currently in vogue field of brain plasticity.

A decade ago, I thought the mind-body problem would never be solved, but I've recently, tentatively, changed my mind.

Philosophers and scientists have long puzzled over how matter — more specifically, gray matter — makes mind, and some have concluded that we'll never find the answer. In 1991 the philosopher Owen Flanagan called these pessimists "mysterians, a term he borrowed from the 1960s rock group "Question Mark and the Mysterians."

One of the earliest mysterians was the German genius Leibniz, who wrote: "Suppose that there be a machine, the structure of which produces thinking, feeling, and perceiving; imagine this machine enlarged but preserving the same proportions, so that you could enter it as if it were a mill… What would you observe there? Nothing but parts which push and move each other, and never anything that could explain perception."

A decade ago I was a hard-core mysterian, because I couldn't imagine what form a solution to the mind-body problem might take. Now I can. If there is a solution, it will come in the form of a neural code, an algorithm, set of rules or syntax that transforms the electrochemical pulses emitted by brain cells into perceptions, memories, decisions, thoughts.

Until recently, a complete decoding of the brain seemed impossibly remote, because technologies for probing living brains were so crude. But over the past decade the temporal and spatial resolution of magnetic resonance imaging, electroencephalography and other external scanning methods has leaped forward. Even more importantly, researchers keep improving the design of microelectrode arrays that can be embedded in the brain to receive messages from — and transmit them to — thousands of individual neurons simultaneously.

Scientists are gleaning information about neural coding not only from non-human animals but also from patients who have had electrodes implanted in their brains to treat epilepsy, paralysis, psychiatric illnesses and other brain disorders. Given these advances, I'm cautiously optimistic that scientists will crack the neural code within the next few decades.

The neural code may resemble relativity and quantum mechanics, in the following sense. These fundamental theories have not resolved all our questions about physical reality. Far from it. Phenomena such as gravity and light still remain profoundly puzzling. Physicists have nonetheless embraced relativity and quantum mechanics because they allow us to predict and manipulate physical reality with extraordinary precision. Relativity and quantum mechanics work.

In the same way, the neural code is unlikely to resolve the mind-body problem to everyone's satisfaction. When it comes to consciousness, many of us seek not an explanation but a revelation, which dispels mystery like sun burning off a morning fog. And yet we will embrace a neural-code theory of mind if it works — that is, if it helps us predict, heal and enhance ourselves. If we can control our minds, who cares if we still cannot comprehend them?

Until I was twenty I was sure there was a being who could see everything I did and who didn't like most of it. He seemed to care about minute aspects of my life, like on what day of the week I ate a piece of meat. And yet, he let earthquakes and mudslides take out whole communities, apparently ignoring the saints among them who ate their meat on the assigned days.  Eventually, I realized that I didn't believe there was such a being. It didn't seem reasonable. And I assumed that I was an atheist. 

As I understood the word, it meant that I was someone who didn't believe in a God; I was without a God. I didn't broadcast this in public because I noticed that people who do believe in a god get upset to hear that others don't. (Why this is so is one of the most pressing of human questions, and I wish a few of the bright people in this conversation would try to answer it through research.) 

But, slowly I realized that in the popular mind the word atheist was coming to mean something more: a statement that there couldn't be a God. God was, in this formulation, not possible, and this was something that could be proved. But I had been changed by eleven years of interviewing six or seven hundred scientists around the world on the television program Scientific American Frontiers. And that change was reflected in how I would now identify myself. 

The most striking thing about the scientists I met was their complete dedication to evidence. It reminded me of the wonderfully plainspoken words of Richard Feynman who felt it was better not to know than to know something that was wrong. The problem for me was that just as I couldn't find any evidence that there was a god, I couldn't find any that there wasn't a god. I would have to call myself an agnostic. At first, this seemed a little wimpy, but after a while I began to hope it might be an example of Feynman's heroic willingness to accept, even glory in, uncertainty. 

I still don't like the word agnostic. It's too fancy. I'm simply not a believer. But, as simple as this notion is, it confuses some people. Someone wrote a Wikipedia entry about me, identifying me as an atheist because I'd said in a book I wrote that I wasn't a believer. I guess in a world uncomfortable with uncertainty, an unbeliever must be an atheist, and possibly an infidel. This gets us back to that most pressing of human questions: why do people worry so much about other people's holding beliefs other than their own? This is the question that makes the subject over which I changed my mind something of global importance, and not just a personal, semantic dalliance.

Do our beliefs identify us the way our language, foods and customs do? Is this why people who think the universe chugs along on its own are as repellent to some as people who eat live monkey brains are to others? Are we saying, you threaten my identity with your infidelity to my beliefs? You're trying to kill me with your thoughts, so I'll get you first with this stone? And, if so, is this really something that can be resolved through reasonable discourse? 

Maybe this is an even more difficult problem; one that's written in the letters that spell out our DNA. Why is the belief in God and Gods so ubiquitous? Does belief in a higher power confer some slight health benefit, and has natural selection favored those who are genetically inclined to believe in such a power — and is that why so many of us are inclined to believe? (Whether or not a God actually exists, the tendency to believe we'll be saved might give us the strength to escape sickness and disaster and live the extra few minutes it takes to replicate ourselves.)

These are wild speculations, of course, and they're probably based on a desperate belief I once had that we could one day understand ourselves. 

But, I might have changed my mind on that one, too.

Some time ago I thought that rational, enlightened thinking would eventually eradicate irrational thinking and supernatural beliefs. How could it be otherwise? Scientists and enlightened people have facts and logical arguments on their side, whereas people 'on the other side' have only unprovable beliefs and bad reasoning. I guess I was wrong, way wrong. Thirty years later, irrational thinking and supernatural beliefs are much stronger than they used to be, permeate ours and other societies and it does not seem they will go away any time soon. How is it possible? Shouldn't 'history' always move forward? What went wrong? What can we do to fix this backward movement toward the irrational?

The problem is that science has still a marginal role in our public discourse. Indeed, there are no science books on the New York Times100 Notable Books of the Year list, no science category in theEconomist Books of the Year 2007 and only Oliver Sacks in the New Yorker's list of Books From Our Pages.

Why does science have such a marginal role? I think there is more than one reason. First, scientists tend to confine themselves in well-defined, narrow boundaries. They tend not to claim any wisdom outside the confines of their specialties. By doing so, they marginalize themselves and make it difficult for science to have an impact on their society. It is high time for scientists to step up and claim wisdom outside their specialty.

There are also other ways, however, to have an impact on our society. For instance, by making some changes in scientific practices. In these days, scientific practices are dominated by the 'hypothesis testing' paradigm. While there is nothing wrong with hypothesis testing, it is definitely wrong to confine all science only to hypothesis testing. This approach precludes the study of complex, real world phenomena, the phenomena that are important to people outside academia. It is time to perform more broad-based descriptive studies on issues that are highly relevant to our society.

Another dominant practice in science (definitely in neuroscience, my own field) is to study phenomena from an atemporal perspective. Only the timeless seems to matter to most neuroscientists. Even time itself tends to be studied from this 'platonic ideal' perspective. I guess this approach stems from the general tendency of science to adopt the detached 'view from nowhere,' as Thomas Nagel puts is. If there is one major thing we have learned from modern science, however, is that there is no such thing, there is no 'view from nowhere.' It is time for scientists (especially neuroscientists) to commit to the study of the finite and temporal. The issues that matter 'here and now' are the issues that people relate to.

How should we do all this? One way of disseminating the scientific method in our public discourse is to use the tools and approaches of science to investigate issues that are salient to the general public. In neuroscience, we have now powerful tools that let us do this. We can study how people make decisions and form affiliations not from a timeless perspective, but from the perspective of what is salient 'here and now.' These are the kind of studies that naturally engage people. While they read about these studies, people are more likely to learn scientific facts (even the 'atemporal' ones) and to absorb the scientific method and reasoning. My hope is that by being exposed to and engaged by scientific facts, methods, and reasoning, people will eventually find it difficult to believe unprovable things.

Six years ago, I changed my mind about the benefit of being able to change my mind.

In 2002, Jane Ebert and I discovered that people are generally happier with decisions when they can't undo them. When subjects in our experiments were able to undo their decisions they tended to consider both the positive and negative features of the decisions they had made, but when they couldn't undo their decisions they tended to concentrate on the good features and ignore the bad. As such, they were more satisfied when they made irrevocable than revocable decisions. Ironically, subjects did not realize this would happen and strongly preferred to have the opportunity to change their minds.

Now up until this point I had always believed that love causes marriage. But these experiments suggested to me that marriage could also cause love. If you take data seriously you act on it, so when these results came in I went home and proposed to the woman I was living with. She said yes, and it turned out that the data were right: I love my wife more than I loved my girlfriend.

The willingness to change one's mind is a sign of intelligence, but the freedom to do so comes at a cost.

For most of my career, I believed that the bedrock of physical reality lay with the laws of physics — magnificent, immutable, transcendent, universal, infinitely-precise mathematical relationships that rule the universe with as sure a hand as that of any god. And I had orthdoxy on my side, for most of my physicist colleagues also believe that these perfect laws are the levitating superturtle that holds up the mighty edifice we call nature, as disclosed through science. About three years ago, however, it dawned on me that such laws are an extraordinary and unjustified idealization.

How can we be sure that the laws are infinitely precise? How do we know they are immutable, and apply without the slightest change from the beginning to the end of time? Furthermore, the laws themselves remain unexplained. Where do they come from? Why do they have the form that they do? Indeed, why do they exist at all? And if there are many possible such laws, then, as Stephen Hawking has expressed it, what is it that "breathes fire" into a particular set of laws and makes a universe for them to govern?

So I did a U turn and embraced the notion of laws as emergent with the universe rather than stamped on it from without like a maker's mark. The "inherent" laws I now espouse are not absolute and perfect, but are instrinsically fuzzy and flexible, although for almost all practical purposes we don't notice the tiny flaws.

Why did I change my mind? I am not content to merely accept the laws of physics as a brute fact. Rather, I want to explain the laws, or at least explain the form they have, as part of the scientific enterprise. One of the oddities about the laws is the well known fact that they are weirdly well-suited to the emergence of life in the universe. Had they been slightly different, chances are there would be no sentient beings around to discover them.

The fashionable explanation for this — that there is a multiplicity of laws in a multiplicity of parallel universes, with each set of laws fixed and perfect within its host universe — is a nice try, but still leaves a lot unexplained. And simply saying that the laws "just are" seems no better than declaring "God made them that way."

The orthodox view of perfect physical laws is a thinly-veiled vestige of monothesim, the reigning world view that prevailed at the birth of modern science. If we want to explain the laws, however, we have to abandon the theological legacy that the laws are fixed and absolute, and replace them with the notion that the states of the world and the laws that link them form a dynamic interdependent unity.

Growing up as a young proto-scientist, I was always strongly anti-establishmentarian, looking forward to overthrowing the System as our generation's new Galileo.  Now I spend a substantial fraction of my time explaining and defending the status quo to outsiders.  It's very depressing.

As an undergraduate astronomy I was involved in a novel and exciting test of Einstein's general relativity — measuring the precession of orbits, just like Mercury in the Solar System, but using massive eclipsing binary stars.  What made it truly exciting was that the data disagreed with the theory!  (Which they still do, by the way.)  How thrilling is it to have the chance to overthrow Einstein himself?  Of course there are more mundane explanations — the stars are tilted, or there is an invisible companion star perturbing their orbits, and these hypotheses were duly considered.  But I wasn't very patient with such boring possibilities — it was obvious to me that we had dealt a crushing blow to a cornerstone of modern physics, and the Establishment was just too hidebound to admit it.

Now I know better.  Physicists who are experts in the field tend to be skeptical of experimental claims that contradict general relativity, not because they are hopelessly encumbered by tradition, but because Einstein's theory has passed a startlingly diverse array of experimental tests.  Indeed, it turns out to be almost impossible to change general relativity in a way that would be important for those binary stars, but which would not have already shown up in the Solar System.  Experiments and theories don't exist in isolation — they form a tightly connected web, in which changes to any one piece tend to reverberate through various others.

So now I find myself cast as a defender of scientific orthodoxy — from classics like relativity and natural selection, to modern wrinkles like dark matter and dark energy.  In science, no orthodoxy is sacred, or above question — there should always be a healthy exploration of alternatives, and I have always enjoyed inventing new theories of gravity or cosmology, keeping in mind the variety of evidence in favor of the standard picture.  But there is also an unhealthy brand of skepticism, proceeding from ignorance rather than expertise, which insists that any consensus must flow from a reluctance to face up to the truth, rather than an appreciation of the evidence.  It's that kind of skepticism that keeps showing up in my email.  Unsolicited.

Heresy is more romantic than orthodoxy.  Nobody roots for Goliath, as Wilt Chamberlain was fond of saying.  But in science, ideas tend to grow into orthodoxy for good reasons.  They fit the data better than the alternatives.  Many casual heretics can't be bothered with all the detailed theoretical arguments and experimental tests that support the models they hope to overthrow — they have a feeling about how the universe should work, and are convinced that history will eventually vindicate them, just as it did Galileo.

What they fail to appreciate is that, scientifically speaking, Galileo overthrew the system from within.  He understood the reigning orthodoxy of his time better than anyone, so he was better able to see beyond it.  Our present theories are not complete, and nobody believes they are the final word on how Nature works.  But finding the precise way to make progress, to pinpoint the subtle shift of perspective that will illuminate a new way of looking at the world, will require an intimate familiarity with our current ideas, and a respectful appreciation of the evidence supporting them. 

Being a heretic can be fun; but being a successful heretic is mostly hard work.

I used to believe that we could understand psychology at different levels of analysis, and events at any one of the levels could be studied independently of events at the other levels. For example, one could study events at the level of the brain (and seek answers in terms of biological mechanisms), the level of the person (and seek answers in terms of the contents of thoughts, beliefs, knowledge, and so forth), or the level of the group (and seek answers in terms of social interactions). This approach seemed reasonable; the strategy of "divide and conquer" is a cornerstone in all of science, isn't it? In fact, virtually all introductory psychology textbooks are written as if events at the different levels are largely independent, with separate chapters (that only rarely include cross-references to each other) on the brain, perception, memory, personality, social psychology, and so on. 

I've changed my mind. I don't think it's possible to understand events at any one level of analysis without taking into account what occurs at other levels. In particular, I'm now convinced that at least some aspects of the structure and function of the brain can only be understood by situating the brain in a specific cultural context. I'm not simply saying that the brain has evolved to function in a specific type of environment (an idea that forms a mainstay of evolutionary psychology and some areas of computer vision, where statistics of the natural environment are used to guide processing). Rather, I'm saying that to understand how any specific brain functions, we need to understand how that person was raised, and currently functions, in the surrounding culture. 

Here's my line of reasoning. Let's begin with a fundamental fact: The genes, of which we have perhaps only some 30,000, cannot program us to function equally effectively in every possible environment. Hence, evolution has licensed the environment to set up and configure each individual's brain, so that it can work well in that context. For example, consider stereovision. We all know about stereo in audition; the sound from each of two loudspeakers has slightly different phases, so the listener's brain glues them together to provide the sense of an auditory panorama. Something similar is at work in vision. In stereovision, the slight disparity in the images that reach the two eyes are a cue for how far away objects are. If you're focused on an object directly in front of you, your eyes will converge slightly. Aside from the exact point of focus, the rest of the image will strike slightly different places on the two retinas (at the back of the eye, which converts light into neural impulses), and the brain uses the slight disparities to figure out how far away something is. 
            
There are two important points here. First, this stereo process — of computing depth on the basis of the disparities in where images strike the two retinas — depends on the distance between the eyes. And second, and this is absolutely critical, there's no way to know at the moment of conception how far apart a person's eyes are going to be, because that depends on bone growth — and bone growth depends partly on the mother's diet and partly on the infant's diet. 
            
So, given that bone growth depends partly on the environment, how could the genes set up stereovision circuits in the brain? What the genes did is really clever: Young children (peaking at about age 18 months) have more connections among neurons than do adults; in fact, until about eight years old, children have about twice as many neural connections as they do as adults. But only some of these connections provide useful information. For example, when the infant reaches, only the connections from some neurons will correctly guide reaching. The brain uses a process called pruning to get rid of the useless connections. The connections that turn out to work, with the distance between the eyes the infant happens to have, would not be the ones that would work if the mother did not have enough calcium, or the infant hadn't had enough of various dietary supplements. 
            
This is a really elegant solution to the problem that the genes can't know in advance how far apart the eyes will be. To cope with this problem, the genes overpopulate the brain, giving us options for different environments (where the distance between eyes and length of the arms are part of the brain's "environment," in this sense), and then the environment selects which connections are appropriate. In other words, the genes take advantage of the environment to configure the brain. 

This overpopulate-and-select mechanism is not limited to stereovision. In general, the environment sets up the brain (above and beyond any role it may have had in the evolution of the species), configuring it to work well in the world a person inhabits. And by environment I'm including everything outside the brain — including the social environment. For example, it's well known that children can learn multiple languages without an accent and with good grammar, if they are exposed to the language before puberty. But after puberty, it's very difficult to learn a second language so well. Similarly, when I first went to Japan, I was told not even to bother trying to bow, that there were something like a dozen different bows and I was always going to "bow with an accent" — and in my case the accent was so thick that it was impenetrable.  
            
The notion is that a variety of factors in our environment, including in our social environment, configure our brains. It's true for language, and I bet it's true for politeness as well as a raft of other kinds of phenomena. The genes result in a profusion of connections among neurons, which provide a playing field for the world to select and configure so that we fit the environment in which we inhabit. The world comes into our head, configuring us. The brain and its surrounding environment are not as separate as they might appear.  

This perspective leads me to wonder whether we can assume that the brains of people living in different cultures process information in precisely the same ways. Yes, people the world over have much in common (we are members of the same species, after all), but even small changes in the wiring may lead us to use the common machinery in different ways. If so, then people from different cultures may have unique perspectives on common problems, and be poised to make unique contributions toward solving such problems. 

Changing my mind about the relationship between events at different levels of analysis has led me to change fundamental beliefs. In particular, I now believe that understanding how the surrounding culture affects the brain may be of more than merely "academic interest."

At age 10 in 1950, one of the department stores had a pneumatic tube system for moving receipts and money from counters to the cashier's office. I loved this and tried to figure out how it worked The clerks in the store knew all about it. "Vacuum", they said, "Vacuum sucks the canisters, just like your mom's vacuum cleaner". But how does it work, I asked? "Vacuum", they said, "Vacuum, does it all". This was what adults called "an explanation"!

So I took apart my mom's Hoover vacuum cleaner to find out how it worked. There was an electric motor in there, which I had expected, but the only other thing in there was a fan! How could a fan produce a vacuum, and how could it suck?

We had a room fan and I looked at it more closely. I knew that it worked like the propeller of an airplane, but I'd never thought about how those worked. I picked up a board and moved it. This moved air just fine. So the blades of the propeller and the fan were just boards that the motor kept on moving to push air.

But what about the vacuum? I found that a sheet of paper would stick to the back of the fan. But why? I "knew" that air was supposed to be made up of particles too small to be seen. So it was clear why you got a gust of breeze by moving a board — you were knocking little particles one way and not another. But where did the sucking of the paper on the fan and in the vacuum cleaner come from?

Suddenly it occurred to me that the air particles must be already moving very quickly and bumping into each other. When the board or fan blades moved air particles away from the fan there were less near the fan and the already moving particles would have less to bump into and would thus move towards the fan. They didn't know about the fan, but they appeared to.

The "suck" of the vacuum cleaner was not a suck at all. What was happening is that things went into the vacuum cleaner because they were being "blown in" by the air particles' normal movement, which were not being opposed by the usual pressure of air particles inside the fan!

When my physiologist father came home that evening I exclaimed "Dad, the air particles must be moving at least a hundred miles an hour!". I told him what I'd found out and he looked in his physics book. In there was a formula to compute the speed of various air molecules at various temperatures. It turned out that at room temperature ordinary air molecules were moving much faster than I had guessed: more like 1500 miles an hour! This completely blew my mind!

Then I got worried because even small things were clearly not moving that fast going into the vacuum cleaner (nor in the pneumatic tubes). By putting my hand out the window of the car I could feel that the air was probably going into the vacuum cleaner closer to 50 or 60 miles an hour. Another conversation with my Dad led to two ideas (a) the fan was probably not very efficient at moving particles away, and (b) the particles themselves were going in every direction and bumping into each other (this is why it takes a while for perfume from an open bottle to be smelled across a room.

This experience was a big deal for me because I had thought one way using a metaphor and a story about "sucking", and then I suddenly thought just the opposite because of an experiment and non-story thinking. The world was not as it seemed! Or as most adults thought and claimed! I never trusted "just a story" again.

I have, falteringly and with various intermediary about-faces and caveats, changed my mind about human spaceflight. I am of the generation to have had its childhood imagination stoked by the sight of Apollo missions on the television — I can't put hand on heart and say I remember the Eagle landing, but I remember the sights of the moon relayed to our homes. I was fascinated by space and only through that, by way of the science fiction that a fascination with space inexorably led to, by science. And astronauts were what space was about.

I was not, as I grew older, uncritical of human spaceflight — I remember my anger at the Challenger explosion, my sense that if people were going to die, it should be for something grander than just another shuttle mission. But I was still struck by its romance, and by the way its romance touched some of the unlikeliest people. By all logic The Economist should have been, when I worked there, highly dubious about the aspirations of human spaceflight, as it is today. But the then editor would hear not a word against the undertaking, at least not against its principle. With some relief at this I became while the magazine's science editor a sort of critical apologist — critical of the human space programme there actually was, but sensitive to the possibility that a better space programme was possible.

I bought into, at least at some level, the argument that a joint US-Russian programme offered advantages in terms of aerospace employment in the former USSR. I bought into the argument that continuity of effort was needed — that so much would be lost if a programme was dismantled it might not be possible to reassemble it. I bought into the crucial safety-net argument — that it would not be possible to cancel the US programme anyway, so strong were the interests of the military industrial complex and so broad, if shallow, the support of the public. (Like the Powder River, a mile wide, an inch deep and rolling uphill all the way from Texas.) And I could see science it would offer that was unavailable by any other means.

Now, though, I can no longer find much to respect in those arguments. US Russian cooperation seems to have bought little benefit. The idea of continuous effort seems at best unproven — and indeed perhaps worth checking. Leaving a technology fallow for a few decades and coming back with new people, tools and mindsets is not such a bad idea. And at least one serious presidential candidate is talking about actually freezing the American programme, cancelling the shuttle without in the short term developing its successor. Whether Obama will get elected or be willing or able to carry through the idea remains to be seen — but if politicians are talking like this the "it will never happen so why worry" argument becomes far more suspect.

And the crucial idea (crucial to me) that human exploration of Mars might answer great questions about life in the universe no longer seems as plausible or as likely to pay off in my lifetime as once it did. I increasingly think that life in a Martian deep biosphere if there is any, will be related to earth life and teach us relatively little that's new. At the same time it will be fiendishly hard to reach without contamination. Mars continues to fascinate me — but it has ever less need of a putative future human presence in order to do so.

My excitement at the idea of life in the universe — excitement undoubtedly spurred by Apollo and the works of Clarke, Heinlein and Roddenberry that followed on from it in my education — is now more engaged with exoplanets, to which human spaceflight is entirely irrelevant (though post-human spaceflight may be a different kettle of lobsters). If we want to understand the depth of the various relations between life and planets, which is what I want to understand, it is by studying other planets with vibrant biospheres, as well as this one, that we will do so. A world with a spartan $100 billion moonbase but no ability to measure spectra and lightcurves from earthlike planets around distant stars is not the world for me.

In general, I try to avoid arguing from my own interests. But in this case it seems to me that all the other arguments against human spaceflight are so strong that to be against it merely meant realising that an atavistic part of me had failed to understand what those interests are. I'm interested in how life works on astronomical scales, and that interest has nothing to do, in the short term, with human spaceflight. And I see no reason beyond my own interests to suggest that it is something worth spending so much money on. It does not make the world a better place in any objective way that can be measured, or in any subjective way that compels respect.

It is possibly also the case that seeing human spaceflight reduced to a matter of suborobital hops for the rich, or even low earth orbit hotels, has hardened my heart further against it. I hope this is not a manifestation of the politics of envy, though I fear that in part it could be.

I have changed my mind about technology.

I used to take a dim view of technology. One should live one's life in a simple, low-tech fashion, I thought. No cell phone, keep off the computer, don't drive. No nukes, no remote control, no DVD, no TV. Walk, read, think — that was the proper path to follow.

What a fool I was! A dozen years ago or so, by some bizarre accident, I became a professor of Mechanical Engineering at MIT. I had never had any training, experience, or education in engineering. My sole claim to engineering expertise was some work on complex systems and a few designs for quantum computers. Quantum-mechanical engineering was in its early days then, however, and MIT needed a quantum mechanic. I was ready to answer the call.

It was not my fellow professors who converted me to technology, uber-techno-nerds though they were. Indeed, my colleagues in Mech. E. were by and large somewhat suspicious of me, justifiably so. I was wary of them in turn, as one often is of co-workers who are hugely more knowledgeable than one is oneself. (Outside of the Mechanical Engineering department, by contrast, I found large numbers of kindred souls: MIT was full of people whose quanta needed fixing, and as a certified quantum mechanic, I was glad to oblige.) No, it was not the brilliant technologists who filled the faculty lunchroom who changed my mind. Rather, it was the students who had come to have me teach them about engineering who taught me to value technology.

Your average MIT undergraduate is pretty technologically adept. In the old days, freshmen used to arrive MIT having disassembled and reassembled tractors and cars; slightly later on, they arrived having built ham radios and guitar amplifiers; more recently, freshmen and fresh women were showing up with a scary facility with computers. Nowadays, few of them have used a screwdriver (except maybe to install some more memory in their laptop), but they are eager to learn how robots work, and raring to build one themselves.

When I stepped into my first undergraduate classroom, a controls laboratory, I knew just about as little about how to build a robot as the nineteen and twenty year olds who were expectantly sitting, waiting for me to teach them how. I was terrified. Within a half an hour, the basis for my terror was confirmed. Not only did I know as little as the students, in many cases I knew significantly less: about of the quarter of the students knew demonstrably more about robotics than I, and were happy to display their knowledge. I emerged from the first lab session a sweaty mess, having managed to demonstrate my ignorance and incompetence in a startling variety of ways.

I emerged  from the second lab session a little cooler. There is no better way to learn, and learn fast, than to teach. Humility actually turns out to have its virtues, too. It turns out to be rather fun to admit one's ignorance, if that admission takes the form of an appeal to the knowledge of all assembled. In fact, it turned out that, either through my training in math and physics, or through a previous incarnation, I possessed more intuitive knowledge of control theory than I had any right to, given my lack of formal education on the subject. Finally, no student is more empowered than the one who has just correctly told her professor that he is wrong, and showed him why her solution is the right one.

In the end, the experience of teaching the technology that I did not know was one of the most intellectually powerful of my life. In my mental ferment of trying to learn the material faster and deeper than my students, I began to grasp concepts and ways of looking at the world, of whose existence I had no previous notion. One of the primary features of the lab was a set of analog computers, boxy things festooned with dials and plugs, and full of amplifiers, capacitors, and resistors, that were used to simulate, or construct an analog, of the motors and loads that we were trying to control. In my feverish attempt to understand analog computers, I constructed model for a quantum-mechanical analog computer that would operate at the level of individual atoms. This model resulted in one of my best scientific papers. In the end, scarily enough, my student evaluations gave me the highest possible marks for knowledge of the material taught.

And technology? Hey, it's not so bad. When it comes to walking in the rain, Goretex and fleece beat oilskin and wool hollow. If we're not going to swamp our world in greenhouse gases, we damn well better design dramatically more efficient cars and power plants. And if I could contribute to technology by designing and helping to build quantum computers and quantum communication systems, so much the better. Properly conceived and constructed technology does not hinder the simple life, but helps it.

OK. So I was wrong about technology. What's my next misconception? Religion? God forbid.

In public appearances about global warming, even these days, I often hear: "I don't believe in global warming" and I then typically get asked why I do "when all the evidence is not in". "Global warming is not about beliefs", I typically retort, "but an accumulation of evidence over decades so that we can now say the vast preponderance of evidence — and its consistency with basic climate theory — supports global warming as well established, not that all aspects are fully known, an impossibility in any complex systems science".

But it hasn't always been that way, especially for me at the outset of my career in 1971, when I co-authored a controversial paper calculating that cooling effects from a shroud of atmospheric dust and smoke — aerosols — from human emissions at a global scale appeared to dominate the opposing warming effect of the growing atmospheric concentrations of the greenhouse gas carbon dioxide. Measurements at the time showed both warming and cooling emissions were on the rise, so a calculation of the net balance was essential — though controlling the aerosols made sense with or without climate side effects since they posed — and still pose — serious health effects on vulnerable populations.  In fact for the latter reason laws to clean up the air in most rich countries were just getting negotiated about that time.

When I traveled the globe in the early 1970s to explain our calculations, what I slowly learned from those out there making measurements was that two facts had only recently come to light, and together they appeared to make me consider flipping sign from cooling to warming as the most likely climatic change direction from humans using the atmosphere as a free sewer to dump some of our volatile industrial and agricultural wastes.  These facts were that human-injected aerosols, which we assumed were global in scale in our cooling calculation — were in fact concentrated primarily in industrial regions and bio-mass burning areas of the globe — about 20% of the Earth's surface, whereas we already knew that CO2 emissions are global in extent and about half of the emitted CO2 lasts for a century or more in the air.

But there were new facts that were even more convincing: not only is CO2 an important human-emitted greenhouse gas, but so too were methane, nitrous oxide and chlorofluorocarbons (many of the latter gases now banned because they also deplete stratospheric ozone) , and that together with CO2, these other greenhouse gasses were an enhanced global set of warming factors. On the other hand, aerosols were primarily regional in extent and could not thus overcome the warming effects of the combined global scale greenhouse gases.

I was very proud to have published in the mid-1970s what was wrong with my early calculations well before the so-called "contrarians" — climate change deniers still all too prevalent even today — understood the issues, let alone incorporated these new facts into updated models to make more credible projections. Of course, today the dominance of warming over cooling agents is now well established in the climatology community, but our remaining inability to be very precise over how much warming the planet can expect to have to deal with is in large part still an uncertainty over the partially counteracting cooling effects of aerosols — enough to offset a significant, even if largely unknown, amount of the warming. So although we are very confident in the existence of human-caused warming in the past several decades from greenhouse gases, we are still are working hard to pin down much more precisely how much aerosols offset this warming. Facts on that offset still lag the critical need to estimate better our impacts on climate before they become potentially irreversible.

The sad part of this story is not about science, but the misinterpretation of it in the political world. I still have to endure polemical blogs from contrarian columnists and others about how, as one put it in a grand polemic: "Schneider is an environmentalist for all temperatures" — citing my early calculations. This famous columnist somehow forgot to bring up the later-corrected (by me) faulty assumptions, nor mention that the 1971 calculation was based on not-yet-gathered facts. Simply getting the sign wrong was cited, ipso facto in this blog, as somehow damning of my current credibility. 

Ironically, inside the scientific world, this switch of sign of projected effects is viewed as precisely what responsible scientists must do when the facts change. Not only did I change my mind, but published almost immediately what had changed and how that played out over time. Scientists have no crystal ball, but we do have modeling methods that are the closest approximation available. They can't give us truth, but they can tell us the logical consequences of explicit assumptions. Those who update their conclusions explicitly as facts evolve are much more likely to be a credible source than those who stick to old stories for political consistency. Two cheers for the scientific method!

I changed my mind about online community this year.

I co-edit a blog that attracts a large number of daily visitors, many of whom have something to say back to us about whatever we write or produce in video. When our audience was small in the early days, interacting was simple: we tacked a little href tag to an open comments thread at the end of each post: Link, Discuss. No moderation, no complication, come as you are, anonymity's fine. Every once in a while, a thread accumulated more noise than signal, but the balance mostly worked.

But then, the audience grew. Fast. And with that, grew the number of antisocial actors, "drive-by trolls," people for whom dialogue wasn't the point. It doesn't take many of them to ruin the experience for much larger numbers of participants acting in good faith.

Some of the more grotesque attacks were pointed at me, and the new experience of being on the receiving end of that much personally-directed nastiness was upsetting. I dreaded hitting the "publish" button on posts, because I knew what would now follow.

The noise on the blog grew, the interaction ceased to be fun for anyone, and with much regret, we removed the comments feature entirely.

I grew to believe that the easier it is to post a drive-by comment, and the easier it is to remain faceless, reputation-less, and real-world-less while doing so, the greater the volume of antisocial behavior that follows. I decided that no online community could remain civil after it grew too large, and gave up on that aspect of internet life.

My co-editors and I debated, we brainstormed, we observed other big sites that included some kind of community forum or comments feature. Some relied on voting systems to "score" whether a comment is of value — this felt clinical, cold, like grading what a friend says to you in conversation. Dialogue shouldn't be a beauty contest. Other sites used other automated systems to rank the relevance of a speech thread. None of this felt natural to us, or an effective way to prevent the toxic sludge buildup. So we stalled for years, and our blog remained more monologue than dialogue. That felt unnatural, too.

Finally, this year, we resurrected comments on the blog, with the one thing that did feel natural. Human hands.

We hired a community manager, and equipped our comments system with a secret weapon: the "disemvoweller." If someone's misbehaving, she can remove all the vowels from their screed with one click. The dialogue stays, but the misanthrope looks ridiculous, and the emotional sting is neutralized.

Now, once again, the balance mostly works. I still believe that there is no fully automated system capable of managing the complexities of online human interaction — no software fix I know of. But I'd underestimated the power of dedicated human attention.

Plucking one early weed from a bed of germinating seeds changes everything. Small actions by focused participants change the tone of the whole. It is possible to maintain big healthy gardens online. The solution isn't cheap, or easy, or hands-free. Few things of value are.

I change my mind all the time — keeping an open mind in science is a good thing. Most often these are rather unremarkable occasions; most often it is acceptance of something I had been unconvinced or unsure about. But then there is this one time …

October 4th, 1995 was a warm day. Florence was overrun by tourists – and a few scientists from a conference I was attending. The next day one of my older and esteemed colleagues from Geneva was going to announce a curious find – a star that seemed to have a very small companion – as small as a planet like Saturn or Jupiter. Such claims had come and gone in the decades past, but this time the data seemed very good. He was keeping the details to himself until the next day, but he told me when I asked him about the orbital period of the new planet. I was incredulous – the period was so short, it was measured in days, not years – I told my wife back in the hotel that night – just 400 days!

I was not a planetary scientist – stars were my specialty, but I knew my planetary basics – a planet like Jupiter could not possibly exist so close to its star and have a period of 400 days. Some of this I had learned as far back as last year of high school. I did not question it, instead I was questioning my colleague’s claim. He was the first to speak the next day and he began by showing the orbital period for the new planet – it was 4.2 days! The night before, I must have heard “4.2 days”, but being so incredibly foreign to my preconception, my brain had “translated” that number to a more “reasonable” 420 days, or – roughly 400. Deeply held preconceptions can be very powerful.

My Florentine experience took some time to sink in. But when it did, it was sobering and inspiring. It made me curious and motivated to find the answers to those questions that just days before I had taken for granted. And I ended up helping develop the new field of extrasolar planets research.

Like many people, I once trusted in the wisdom of Nature. I imagined that there were real boundaries between the natural and the artificial, between one species and another, and thought that, with the advent of genetic engineering, we would be tinkering with life at our peril. I now believe that this romantic view of Nature is a stultifying and dangerous mythology.

Every 100 million years or so, an asteroid or comet the size of a mountain smashes into the earth, killing nearly everything that lives. If ever we needed proof of Nature's indifference to the welfare of complex organisms such as ourselves, there it is. The history of life on this planet has been one of merciless destruction and blind, lurching renewal.

The fossil record suggests that individual species survive, on average, between one and ten million years. The concept of a "species" is misleading, however, and it tempts us to think that we, as homo sapiens, have arrived at some well-defined position in the natural order. The term "species" merely designates a population of organisms that can interbreed and produce fertile offspring; it cannot be aptly applied to the boundaries between species (to what are often called "intermediate" or "transitional" forms). There was, for instance, no first member of the human species, and there are no canonical members now. Life is a continuous flux. Our nonhuman ancestors bred, generation after generation, and incrementally begat what we now deem to be the species homo sapiens — ourselves.  There is nothing about our ancestral line or about our current biology that dictates how we will evolve in the future. Nothing in the natural order demands that our descendants resemble us in any particular way. Very likely, they will not resemble us. We will almost certainly transform ourselves, likely beyond recognition, in the generations to come.

Will this be a good thing? The question presupposes that we have a viable alternative. But what is the alternative to our taking charge of our biological destiny? Might we be better off just leaving things to the wisdom of Nature? I once believed this. But we know that Nature has no concern for individuals or for species. Those that survive do so despite Her indifference. While the process of natural selection has sculpted our genome to its present state, it has not acted to maximize human happiness; nor has it necessarily conferred any advantage upon us beyond the capacity raise the next generation to child-bearing age.  In fact, there may be nothing about human life after the age of forty (the average lifespan until the 20th century) that has been selected by evolution at all. And with a few exceptions (e.g. the gene for lactose tolerance), we probably haven't adapted to our environment much since the Pleistocene.

But our environment and our needs — to say nothing of our desires — have changed radically in the meantime. We are in many respects ill-suited to the task of building a global civilization. This is not a surprise. From the point of view of evolution, much of human culture, along with its cognitive and emotional underpinnings, must be epiphenomenal. Nature cannot "see" most of what we are doing, or hope to do, and has done nothing to prepare us for many of the challenges we now face.

These concerns cannot be waved aside with adages like, "if it ain't broke, don't fix it." There are innumerable perspectives from which our current state of functioning can be aptly described as "broke." Speaking personally, it seems to me that everything I do picks out some point on a spectrum of disability: I was always decent at math, for instance, but this is simply to say that I am like a great mathematician who has been gored in the head by a bull; my musical ability resembles that of a Mozart or a Bach, it is true, though after a near fatal incident on skis; if Tiger Woods awoke from surgery to find that he now possessed (or was possessed by) my golf-swing, rest assured that a crushing lawsuit for medical malpractice would be in the offing.

Considering humanity as a whole, there is nothing about natural selection that suggests our optimal design. We are probably not even optimized for the Paleolithic, much less for life in the 21st century. And yet, we are now acquiring the tools that will enable us to attempt our own optimization. Many people think this project is fraught with risk. But is it riskier than doing nothing? There may be current threats to civilization that we cannot even perceive, much less resolve, at our current level of intelligence. Could any rational strategy be more dangerous than following the whims of Nature? This is not to say that our growing capacity to meddle with the human genome couldn't present some moments of Faustian over-reach. But our fears on this front must be tempered by a sober understanding of how we got here. Mother Nature is not now, nor has she ever been, looking out for us.

Aside from whether Apple matters (whoops!), the biggest thing I've changed my mind about is climate change. There was no one thing that convinced me to flip from wait-and-see to the-time-for-debate-is-over. Instead, there were three things, which combined for me in early 2006. There was, of course, the scientific evidence, which kept getting more persuasive. There was also economics, and the recognition that moving to alternative, sustainable energy was going to be cheaper over the long run as oil got more expensive. And finally there was geopolitics, with ample evidence of how top-down oil riches destabilized a region and then the world. No one reason was enough to win me over to total energy regime change, but together they seemed win-win-win.

Now I see the entire energy and environmental picture through a carbon lens. It's very clarifying. Put CO2 above everything else, and suddenly you can make reasonable economic calculations about risks and benefits, without getting caught up in the knotty politics of full-spectrum environmentalism. I was a climate skeptic and now I'm a carbon zealot. I seem to annoy traditional environmentalists just as much, but I like to think that I've moved from behind to in front.

I've changed my mind about the manner in which our future on this planet might evolve.

I used to think that the power of science to dissect, inform, illuminate and clarify, its venerable record in improving the human condition, and its role in enabling the technological progress of the modern world were all so glaringly obvious that no one could reasonably question its hallowed position in human culture as the pre-eminent device for separating truth from falsehood.

I used to think that the edifice of knowledge constructed from thousands of years of scientific thought by various cultures all over the globe, and in particular the insights earned over the last 400 years from modern scientific methods, were so universally revered that we could feel comfortably assured of having permanently left our philistine days behind us.

And while I've always appreciated the need for care and perseverance in guiding public evaluation of the complexities of scientific discourse and its findings, I never expected that we would, at this stage in our development, have to justify and defend the scientific process itself.

Yet, that appears to be the case today. And now, I'm no longer sure that scientific inquiry and the cultural value it places on verifiable truth can survive without constant protection, and its ebb and flow over the course of human history affirms this. We have been beset in the past by dark ages, when scientific truths and the ideas that logically spring from them were systematically destroyed or made otherwise unavailable, when the practitioners of science were discredited, imprisoned, and even murdered. Periods of human enlightenment have been the exception throughout time, not the rule, and our language has acknowledged this: 'Two steps forward, one step back' neatly outlines the nonmonotonic stagger inherent in any reading of human history.

And, if we're not mindful, we could stagger again. When the truth becomes problematic, when intellectual honesty clashes with political expediency, when voices of reason are silenced to mere whisper, when fear alloys with ignorance to promote might over intelligence, integrity, and wisdom, the very practice of science can find itself imperiled. At that point, can darkness be far behind?

To avoid so dangerous a tipping point requires us, first and foremost, to recognize the distasteful possibility that it could happen again, at any time. I now suspect the danger will be forever present, the need for vigilance forever great.

I was an earnest student in Catechism class. The climax of our early training, as thirteen year-olds, was an intense retreat in preparation for the sacrament of Confirmation. Even now I vividly remember the rapture of belief, the glow everyday events acquired when I felt that they reflected a grand scheme of the universe, in which I had a personal place. Soon afterward, though, came disillusionment. As I learned more about science, some of the concepts and explanations in the ancient sacred texts came to seem clearly wrong; and as I learned more about history and how it is recorded, some of the stories in those texts came to seem very doubtful.

What I found most disillusioning, however, was not that the sacred texts contained errors, but that they suffered by comparison. Compared to what I was learning in science, they offered few truly surprising and powerful insights. Where was there a vision to rival the concepts of infinite space, of vast expanses of time, of distant stars that rivaled and surpassed our Sun? Or of hidden forces and new, invisible forms of "light"? Or of tremendous energies that humans could, by understanding natural processes, learn to liberate and control? I came to think that if God exists, He (or She, or They, or It ) did a much more impressive job revealing Himself in the world than in the old books; and that the power of faith and prayer is elusive and unreliable, compared to the everyday miracles of medicine and technology.

For many years, like some of my colleagues and some recent bestselling authors, I thought that active, aggressive debunking might be in order. I've changed my mind. One factor was my study of intellectual history. Many of my greatest heros in physics, including Galileo, Newton, Faraday, Maxwell, and Planck, were deeply religious people. They truly believed that what they were doing, in their scientific studies, was discovering the mind of God. Many of Bach's and Mozart's most awesome productions are religiously inspired. Saint Augustine's writings display one of the most impressive intellects ever. And so on. Can you imagine hectoring this group? And what would be the point? Did their religious beliefs make them stupid, or stifle their creativity?

Also, debunking hasn't worked very well. David Hume already set out the main arguments for religious skepticism in the early eighteenth century. Bertrand Russell and many others have augmented them since. Textual criticism reduces fundamentalism to absurdity. Modern molecular biology, rooted in physics and chemistry, demonstrates that life is a natural process; Darwinian evolution illuminates its natural origin. These insights have been highly publicized for many decades, yet religious doctrines that contradict some or all of them have not merely survived, but prospered.

Why? Part of the answer is social. People tend to stay with the religion of their birth, for the same sorts of reasons that they stay loyal to their clan, or their country.

But beyond that, religion addresses some deep concerns that science does not yet, for most people, touch. The human yearning for meaningful understanding, our fear of death — these deep motivations are not going to vanish. 

Understanding, of course, is what science is all about. Many people imagine, however, that scientific understanding is dry and mundane, with no scope for wonder and amazement. That is simply ignorant. Looking for wonder and amazement? Try some quantum theory!

Beyond understanding inter-connected facts, people want to discover their significance or meaning. Neuroscientists are beginning to map human motivations and drives at the molecular level. As this work advances, we will attain a deeper understanding of the meaning of meaning. Freud's theories had enormous impact, not because they are correct, but because they "explained" why people feel and act as they do. Correct and powerful theories that address these issues are sure to have much greater impact.

Meanwhile, medical science is taking a deep look at aging. Within the next century, it may be possible for people to prolong youth and good health for many years — perhaps indefinitely. This would, of course, profoundly change our relationship with death. So to me the important challenge is not to debunk religion, but to address its issues in better ways.

I have changed my mind about the general validity of the mechanical worldview that underlies the modern scientific understanding of natural processes. Trained in biology and mathematics, I have used the scientific approach to the explanation of natural phenomena during most of my career. The basic assumption is that whatever properties and behaviours have emerged naturally during cosmic evolution can all be understood in terms of the motions and interactions of inanimate entities such as elementary particles, atoms, molecules, membranes and organelles, cells, organs, organisms, and so on.

Modelling natural processes on the basis of these assumptions has provided explanations for myriad natural phenomena ranging from planetary motion and electromagnetic phenomena to the properties and behaviour of nerve cell and the dynamic patterns that emerge in ant colonies or flocks of birds. There appeared to be no limit to the power of this explanatory procedure, which enchanted me and kept me busy throughout most of my scientific career in biology.

However, I have now come to the conclusion that this method of explaining natural phenomena has serious limitations, and that these come from the basic assumptions on which it is based. The crunch came for me with the "explanation" of qualitative experience in humans and other organisms. By this I mean the experience of pain or pleasure or wellbeing, or any other of the qualities that are very familiar to us.

These are described as "subjective", that is, experienced by a living organism, because they cannot be isolated from the subject experiencing them and measured quantitatively. What is often suggested as an explanation of this is evolutionary complexity: when an organism has a nervous system of sufficient complexity, subjective experience and feelings can arise. This implies that something totally new and qualitatively different can emerge from the interaction of "dead", unfeeling components such as cell membranes, molecules and electrical currents.

But this implies getting something from nothing, which violates what I have learned about emergent properties: there is always a precursor property for any phenomenon, and you cannot just introduce a new dimension into the phase space of your model to explain the result. Qualities are different from quantities and cannot be reduced to them.

So what is the precursor of the subjective experience that evolves in organisms? There must be some property of neurones or membranes or charged ions producing the electric associated with the experience of feeling that emerges in the organism.

One possibility is to acknowledge that the world isn't what modern science assumes it to be, mechanical and "dead", but that everything has some basic properties relating to experience or feeling. Philosophers and scientists have been down this route before, and have called this pan-sentience or pan-psychism: the world is impregnated with some form of feeling in every one of its constituents. This makes it possible for the evolution of complex organised beings such as organisms to develop feelings and for qualities to be as real as quantities.

Pan-sentience shifts science into radically new territory. Science can now be about qualities as well as quantities, helping us to recover quality of life, to heal our relationship to the natural world, and to undo the damage we are causing to the earth's capacity to continue its evolution with us. It could help us to recover our place as participants in a world that is not ours to control, but is ours to contribute to creatively, along with all the other diverse members of our living, feeling, planetary society.

I've changed my mind about the use of enhancement drugs by healthy people. A year ago, if asked, I'd have been against the idea, whereas now I think there's much to be said for it.

The ultimate test of such a change of mind is how I'd feel if my offspring (both adults) went down that road, and my answer is that with tolerable risks of side effects and zero risk of addiction, then I'd feel OK if there was an appropriate purpose to it. 'Appropriate purposes' exclude gaining an unfair advantage or unwillingly following the demands of others, but include gaining a better return on an investment of study or of developing a skill.

I became interested in the issues surrounding cognitive enhancement as one example of debates about human enhancement — debates that can only get more vigorous in future. It's also an example of a topic in which both natural and social sciences can contribute to better regulation — another theme that interests me. Thinking about the issues and looking at the evidence-based literatures made me realise how shallow was my own instinctive aversion to the use of such drugs by healthy people. It also led to a thoughtful article by Barbara Sahakian and Sharon Morein-Zamir in Nature (20 December 2007) that triggered many blog discussions.

Social scientists report that a small but significant proportion of students on at least some campuses are using prescription drugs in order to help their studies — drugs such as modafinil (prescribed for narcolepsy) and methylphenidate (prescribed for attention-deficit hyperactivity disorder). I've not seen studies that quantify similar use by academic faculty, or by people in other non-military walks of life, though there is no doubt that it is happening. There are anecdotal accounts and experimental small-scale trials showing that such drugs do indeed improve performance to a modest degree under particular circumstances.

New cognitive enhancing drugs are being developed, officially for therapy. And the therapeutic importance — both current and potential — of such drugs is indeed significant. But manufacturers won't turn away the significant revenues from illegal use by the healthy.

That word 'illegal' is the rub. Off-prescription use is illegal in the United States, at least. But that illegality reflects an official drugs culture that is highly questionable. It's a culture in which the Food and Drugs Administration seems reluctant generally to embrace the regulation of enhancement for the healthy, though it is empowered to do so. It is also a culture that is rightly concerned about risk but wrongly founded in the idea that drugs used by healthy people are by definition a Bad Thing. That in turn reflects instinctive attitudes to do with 'naturalness' and 'cheating on yourself' that don't stand up to rational consideration. Perhaps more to the point, they don't stand up to behavioral consideration, as Viagra has shown.

Research and societal discussions are necessary before cognitive enhancement drugs should be made legally available for the healthy, but I now believe that that is the right direction in which to head.

With reference to the precursor statements of this year's annual question, there are facts behind that change of mind, some thinking, and some secular faith in humans, too.

When I first heard about the solar neutrino puzzle, I had a little trouble taking it seriously. We know that the sun is powered by a chain of nuclear reactions and that in addition to emitting energy these reactions lead to the emission of neutrinos (uncharged fundamental particles that interact only via the weak nuclear force). The original solar neutrino puzzle was that when physicists made experiments to find these neutrinos, none of them were detected. But by the time I learned about the puzzle, physicists had in fact observed solar neutrinos — only the amount they found was only about 1/3 - 1/2 of the amount that other physicists had predicted. But I was skeptical that this deficit was really a problem — how could we make such an accurate prediction about the sun — an object 93 million miles away about which we can measure only so much? To give one example, the prediction for the neutrino flux was strongly temperature-dependent.   Did we really know the temperature sufficiently accurately? Were we sure we understood heat transport inside the sun well enough to trust this prediction?

But I ended up changing my mind (along with many other initially skeptical physicists). The solar neutrino puzzle turned out to be a clue to some very interesting physics. It turns out that neutrinos mix. Every neutrino is labeled by the charged lepton with which it interacts via the weak nuclear force.  (Charged leptons are particles like electrons — there are two heavier versions known as muons and taus.)  It turns out the neutrinos have a bit of an identity crisis and can convert into each other as they travel through the sun and as they make their way to Earth.  An electron neutrino can change into a tau neutrino. Since detectors were looking only for electron neutrinos, they missed the ones that had converted. And that was the very elegant solution to the solar neutrino puzzle. The predictions based on what we knew about the Standard Model of particle physics (that tells us what are the fundamental particles and forces)  had been correct — hence change of mind #1. But the prediction had been inaccurate because no one had yet measured the masses and mixing angles of neutrinos. Subsequent experiments have searched for all types of neutrinos — not just electron neutrinos — and found the different neutrino types, thereby confirming the mixing.

And that leads me to a second thing I changed my mind about (along with much of the particle physics community). These neutrino mixing angles turned out to be big. That is, a significant fraction of electron neutrinos turn into muon neutrinos, and a big fraction of muon neutrinos turn into tau neutrinos (here it was neutrinos in the atmosphere that had gone missing).  Few physicists had thought these mixing angles would be big. That is because similar angles in the quark sector (quarks are particles such as the up and down quarks inside protons and neutrons that interact via the strong nuclear force) are much smaller. Everyone based their guess on what was already known. These big neutrino mixing angles were a real surprise — perhaps the biggest surprise from particle physics measurements since I started studying the field.

Why are these angles important? First of all neutrino mixing does in fact explain the missing neutrinos from the sun and from the atmosphere. But these angles are also are an important clue as to the nature of the fundamental particles of which all known matter is made.   One of the chief open questions about these particles is why there are three "copies" of the known particle types — that is heavier versions with identical charges?  Another is why do these different versions have different masses? And a third question is why do these particles mix in the way they have been measured to do? When we understand the answers to these questions we will have a much greater insight into the fundamental nature of all known matter. We don't know yet if we'll get the right answers but  these questions pose important challenges. And when we find the answer is is likely at this point that neutrinos will provide a clue.

In November 2002, Clay Shirky organized a "social software summit," based on the premise that we were entering a "golden age of social software... greatly extending the ability of groups to self-organize."

I was skeptical of the term "social software" at the time. The explicit social software of the day, applications like friendster and meetup, were interesting, but didn't seem likely to be the seed of the next big Silicon Valley revolution.

I preferred to focus instead on the related ideas that I eventually formulated as "Web 2.0," namely that the internet is displacing Microsoft Windows as the dominant software development platform, and that the competitive edge on that platform comes from aggregating the collective intelligence of everyone who uses the platform. The common thread that linked Google's PageRank, ebay's marketplace, Amazon's user reviews, Wikipedia's user-generated encyclopedia, and CraigsList's self-service classified advertising seemed too broad a phenomenon to be successfully captured by the term "social software." (This is also my complaint about the term "user generated content.") By framing the phenomenon too narrowly, you can exclude the exemplars that help to understand its true nature. I was looking for a bigger metaphor, one that would tie together everything from open source software to the rise of web applications.

You wouldn't think to describe Google as social software, yet Google's search results are profoundly shaped by its collective interactions with its users: every time someone makes a link on the web, Google follows that link to find the new site. It weights the value of the link based on a kind of implicit social graph (a link from site A is more authoritative than one from site B, based in part on the size and quality of the network that in turn references either A or B). When someone makes a search, they also benefit from the data Google has mined from the choices millions of other people have made when following links provided as the result of previous searches.

You wouldn't describe ebay or Craigslist or Wikipedia as social software either, yet each of them is the product of a passionate community, without which none of those sites would exist, and from which they draw their strength, like Antaeus touching mother earth. Photo sharing site Flickr or bookmark sharing site del.icio.us (both now owned by Yahoo!) also exploit the power of an internet community to build a collective work that is more valuable than could be provided by an individual contributor. But again, the social aspect is implicit — harnessed and applied, but never the featured act.

Now, five years after Clay's social software summit, Facebook, an application that explicitly explores the notion of the social network, has captured the imagination of those looking for the next internet frontier. I find myself ruefully remembering my skeptical comments to Clay after the summit, and wondering if he's saying "I told you so."

Mark Zuckerberg, Facebook's young founder and CEO, woke up the industry when he began speaking of "the social graph" — that's computer-science-speak for the mathematical structure that maps the relationships between people participating in Facebook — as the core of his platform. There is real power in thinking of today's leading internet applications explicitly as social software.

Mark's insight that the opportunity is not just about building a "social networking site" but rather building a platform based on the social graph itself provides a lens through which to re-think countless other applications. Products like xobni (inbox spelled backwards) and MarkLogic's MarkMail explore the social graph hidden in our email communications; Google and Yahoo! have both announced projects around this same idea. Google also acquired Jaiku, a pioneer in building a social-graph enabled address book for the phone.

This is not to say that the idea of the social graph as the next big thing invalidates the other insights I was working with. Instead, it clarifies and expands them:

• Massive collections of data and the software that manipulates those collections, not software alone, are the heart of the next generation of applications.
• The social graph is only one instance of a class of data structure that will prove increasingly important as we build applications powered by data at internet scale. You can think of the mapping of people, businesses, and events to places as the "location graph", or the relationship of search queries to results and advertisements as the "question-answer graph."
• The graph exists outside of any particular application; multiple applications may explore and expose parts of it, gradually building a model of relationships that exist in the real world.
• As these various data graphs become the indispensable foundation of the next generation "internet operating system," we face one of two outcomes: either the data will be shared by interoperable applications, or the company that first gets to a critical mass of useful data will become the supplier to other applications, and ultimately the master of that domain.

So have I really changed my mind? As you can see, I'm incorporating "social software" into my own ongoing explanations of the future of computer applications.

It's curious to look back at the notes from that first Social Software summit. Many core insights are there, but the details are all wrong. Many of the projects and companies mentioned have disappeared, while the ideas have moved beyond that small group of 30 or so people, and in the process have become clearer and more focused, imperceptibly shifting from what we thought then to what we think now.

Both Clay, who thought then that "social software" was a meaningful metaphor and I, who found it less useful then than I do today, have changed our minds. A concept is a frame, an organizing principle, a tool that helps us see. It seems to me that we all change our minds every day through the accretion of new facts, new ideas, new circumstances. We constantly retell the story of the past as seen through the lens of the present, and only sometimes are the changes profound enough to require a complete repudiation of what went before.

Ideas themselves are perhaps the ultimate social software, evolving via the conversations we have with each other, the artifacts we create, and the stories we tell to explain them.

Yes, if facts change our mind, that's science. But when ideas change our minds, we see those facts afresh, and that's history, culture, science, and philosophy all in one.

In January of 2007, China's president, Hu Jintao, gave a speech before a group of Communist Party officials. His subject was the Internet. "Strengthening network culture construction and management," he assured the assembled bureaucrats, "will help extend the battlefront of propaganda and ideological work. It is good for increasing the radiant power and infectiousness of socialist spiritual growth."

If I had read those words a few years earlier, they would have struck me as ludicrous. It seemed so obvious that the Internet stood in opposition to the kind of centralized power symbolized by China's regime. A vast array of autonomous nodes, not just decentralized but centerless, the Net was a technology of personal liberation, a force for freedom.

I now see that I was naive. Like many others, I mistakenly interpreted a technical structure as a metaphor for human liberty. In recent years, we have seen clear signs that while the Net may be a decentralized communications system, its technical and commercial workings actually promote the centralization of power and control. Look, for instance, at the growing concentration of web traffic. During the five years from 2002 through 2006, the number of Internet sites nearly doubled, yet the concentration of traffic at the ten most popular sites nonetheless grew substantially, from 31% to 40% of all page views, according to the research firm Compete.

Or look at how Google continues to expand its hegemony over web searching. In March 2006, the company's search engine was used to process a whopping 58% of all searches in the United States, according to Hitwise. By November 2007, the figure had increased yet again, to 65%. The results of searches are also becoming more, not less, homogeneous. Do a search for any common subject, and you're almost guaranteed to find Wikipedia at or near the top of the list of results. 

It's not hard to understand how the Net promotes centralization. For one thing, its prevailing navigational aids, such as search engine algorithms, form feedback loops. By directing people to the most popular sites, they make those sites even more popular. On the web as elsewhere, people stream down the paths of least resistance.

The predominant means of making money on the Net — collecting small sums from small transactions — also promotes centralization. It is only by aggregating vast quantities of content, data, and traffic that businesses can turn large profits. That's why companies like Microsoft and Google have been so aggressive in buying up smaller web properties. Google, which has been acquiring companies at the rate of about one a week, has disclosed that its ultimate goal is to "store 100% of user data."

As the dominant web companies grow, they are able to gain ever larger economies of scale through massive capital investments in the "server farms" that store and process online data. That, too, promotes consolidation and centralization. Executives of Yahoo and Sun Microsystems have recently predicted that control over the net's computing infrastructure will ultimately lie in the hands of five or six organizations.

To what end will the web giants deploy their power? They will, of course, seek to further their own commercial or political interests by monitoring, analyzing, and manipulating the behavior of "users." The connection of previously untethered computers into a single programmable system has created "a new apparatus of control," to quote NYU's Andrew Galloway. Even though the Internet has no center, technically speaking, control can be wielded, through software code, from anywhere. What's different, in comparison to the physical world, is that acts of control are more difficult to detect.

So it's not Hu Jintao who is deluded in believing that the net might serve as a powerful tool for central control. It is those who assume otherwise. I used to count myself among them. But I've changed my mind.

Often a new field comes along purporting to offer bold new insights into questions that have long vexed us. And often, after the initial excitement dies down, that field turns out to really only offer a bunch of new names for stuff we basically already knew. I used to think neuroeconomics was such a field. But I was wrong.

Neuroeconomics mixes brain science with the dismal science — throwing in some evolutionary psychology and elements of prospect theory as developed by Daniel Kahneman and Amos Tversky — to explain the emotional and psychological quirks of human economic behavior. To take a common example — playing the stock market. Our brains are always prospecting for pattern. Researchers at Duke University showed people randomly generated sequences of circles and squares. Whenever two consecutive circles or squares appeared, the subjects' nucleus accumbens — the part of the brain that's active whenever a stimulus repeats itself — went into overdrive, suggesting the participants expected a third circle or square to continue the sequence.

The stock market is filled with patterns. But the vast majority of those patterns are meaningless, at least in the short term. The hourly variance of a stock price, for example, is far less significant than its annual variance. When you're checking your portfolio every hour, the noise in those statistics drowns out any real information. But our brains evolved to detect patterns of immediate significance, and the nucleus accumbens sends a jolt of pleasure into the investor who thinks he's spotted a winner. Yet studies consistently show that people who follow their investments closely earn lower returns than those who don't pay much attention at all. Why? Because their nucleus accumbens isn't prompting them to make impulsive decisions based on momentary patterns they think they've detected.

The beauty of neuroeconomics is that it's easily verified by personal experience. A while back, I had stock options that I had to exercise within a specific period of time. So I started paying attention to the markets on a daily basis, something I normally never do. I was mildly encouraged every time the stock price ratcheted up a notch or two, smugly satisfied that I hadn't yet cashed in my options. But I was devastated when the price dropped back down again, recriminating myself for missing a golden opportunity. (This was Kahneman and Tversky's "loss aversion" — the tendency to strongly prefer to avoid a loss rather than to acquire a gain — kicking in. Some studies suggest that the fear of a loss has twice the psychological impact as the lure of a gain.) I eventually exercised my options after the price hit a level it hadn't reached for several years. I was pretty pleased with myself — until the firm sold some of its businesses a few weeks later and the stock price shot up by several dollars.

Neuroeconomics really does explain the non-rational aspects of human economic behavior; it is not just another way of saying there's a sucker born every minute. And now, thanks to this new field, I can blame my bad investment decisions on my nucleus accumbens rather than my own stupidity.

The words "science" and "technology," or equivalently the words "research" and "development," are used in the same breath so readily that one might easily presume that they are joined at the hip: that their goals are indistinguishable, and that those who are good at one are, if not necessarily equally good at the other, at least quite good at evaluating the quality of work in the other. I grew up with this assumption, but the longer I work at the interface between science and technology the more I find myself having to accept that it is false — that most, scientists are rather poor at the type of thinking that identifies efficient new ways to get things done, and that, likewise, technologists are mostly not terribly good at identifying efficient ways to find things out.

I've come to feel that there are several reasons underlying this divide.

A major one is the divergent approaches of scientists and technologists to the use of evidence. In basic research, it is exceptionally easy to be seduced by one's data — to see a natural interpretation of it and to overlook the existence of other, comparably economical interpretations of it that lead to dramatically different conclusions. It therefore makes sense for scientists to give the greatest weight, when evaluating the evidence for and against a given hypothesis, to the most direct observational or experimental evidence at hand.

Technologists, on the other hand, succeed best when they stand back from the task before them, thinking laterally about ways in which ostensibly irrelevant techniques might be applied to solve one or another component of the problem. The technologist's approach, when applied to science, is likely to result all too often in wasted time, as experiments are performed that contain too many departures from previous work to allow the drawing of firm conclusions either way concerning the hypothesis of interest.

Conversely, applying the scientist's methodology to technological endeavours can also result in wasted time, resulting from overly small steps away from techniques already known to be futile, like trying to fly by flapping mechanical wings.

But there's another difference between the characteristic mindsets of scientists and technologists, and I've come to view it as the most problematic. Scientists are avowedly "curiosity-driven" rather than "goal-directed" — they are spurred by the knowledge that, throughout the history of civilisation, innumerable useful technologies have become possible not through the stepwise execution of a predefined plan, but rather through the purposely undirected quest for knowledge, letting a dynamically-determined sequence of experiments lead where it may.

That logic is as true as it ever was, and any technologist who doubts it need only examine the recent history of science to change his mind. However, it can be — and, in my view, all too often is — taken too far. A curiosity-driven sequence of experiments is useful not because of the sequence, but because of the technological opportunities that emerge at the end of the sequence. The sequence is not an end in itself. And this is rather important to keep in mind. Any scientist, on completing an experiment, is spoilt for choice concerning what experiment to do next — or, more prosaically, concerning what experiment to apply for funding to do next.

The natural criterion for making this choice is the likelihood that the experiment will generate a wide range of answers to technologically important questions, thereby providing new technological opportunities. But an altogether more frequently adopted criterion, in practice, is that the experiment will generate a wide range of new questions — new reasons to do more experiments. This is only indirectly useful, and I believe that in practice it is indeed less frequently useful than programs of research designed with one eye on the potential for eventual technological utility.

Why, then, is it the norm? Simply because it is the more attractive to those who are making these decisions — the curiosity-driven scientists (whether the grant applicants or the grant reviewers) themselves. Curiosity is addictive: both emotionally and in their own enlightened self-interest, scientists want reasons to do more science, not more technology. But as a society we need science to be as useful as possible, as quickly as possible, and this addiction slows us down.

One of my most basic assumptions about the relationship between mental effort and brain function has begun to crumble. Here's why.

My earliest research interests as a psychologist were in the ways mental training can shape biological systems.  My doctoral dissertation was a psychophysiological study of meditation as an intervention in stress reactivity; I found (as have many others since) that the practice of meditation seems to speed the rate of physiological recovery from a stressor.

My guiding assumptions included the standard premise that the mind-body relationship operates according to orderly, understandable principles.  One such might be called the "dose-response" rule, that the more time put into a given method of training, the greater the result in the targeted biological system.  This is a basic correlate of neuroplasticity, the mechanism through which repeated experience shapes the brain.

For example, a string of research has now established that more experienced meditators recover more quickly from stress-induced physiological arousal than do novices. Nothing remarkable there.  The dose-response rule would predict this is so. Thus brain imaging studies show that the spatial areas of London taxi drivers become enhanced during the first six months they spend driving around that city's winding streets; likewise, the area for thumb movement in the motor cortex becomes more robust in violinists as they continue to practice over many months.

This relationship has been confirmed in many varieties of mental training. A seminal 2004 article in the Proceedings of the National Academy of Science found that, compared to novices, highly adept meditators generated far more high-amplitude gamma wave activity — which reflects finely focused attention — in areas of the prefrontal cortex while meditating.

The seasoned meditators in this study — all Tibetan lamas — had undergone cumulative levels of mental training akin to the amount of lifetime sports practice put in by Olympic athletes: 10,000 to 50,000 hours. Novices tended to increase gamma activity by around 10 to 15 percent in the key brain area, while most experts had increases on the order of 100 percent from baseline. What caught my eye in this data was not this difference between novices and experts (which might be explained in any number of ways, including a self-selection bias), but rather a discrepancy in the data among the group of Olympic-level meditators.

Although the experts' average boost in gamma was around 100 percent, two lamas were "outliers": their gamma levels leapt 700 to 800 percent. This goes far beyond an orderly dose-response relationship — these jumps in high-amplitude gamma activity are the highest ever reported in the scientific literature apart from pathological conditions like seizures. Yet the lamas were voluntarily inducing this extraordinarily heightened brain activity for just a few minutes at a time — and by meditating on "pure compassion," no less.

I have no explanation for this data, but plenty of questions. At the higher reaches of contemplative expertise, do principles apply (as the Dalai Lama has suggested in dialogues with neuroscientists) that we do not yet grasp? If so, what might these be? In truth, I have no idea. But these puzzling data points have pried open my mind a bit as I've had to question what had been a rock-solid assumption of my own.

In a 2007 radio advertisement, former NYC mayor Rudy Giuliani said, "I had prostate cancer, five, six years ago. My chances of surviving prostate cancer — and thank God I was cured of it — in the United States: 82 percent. My chances of surviving prostate cancer in England: only 44 percent under socialized medicine." Giuliani was lucky to be living in New York, and not in York — true?

In World Brain (1938), H. G. Wells predicted that for an educated citizenship in a modern democracy, statistical thinking would be as indispensable as reading and writing. At the beginning of the 21st century, we have succeeded in teaching millions how to read and write, but many of us still don't know how to reason statistically — how to understand risks and uncertainties in our technological world.

Giuliani is a case in point. One basic concept that everyone should understand is the 5-year survival rate. Giuliani used survival rates from the year 2000, where 49 Britons per 100,000 were diagnosed of prostate cancer, of which 28 died within 5 years — about 44 percent. Is it true that his chances of surviving cancer are about twice as high in what Giuliani believes is the best health care system in the world? Not at all. Survival rates are not the same as mortality rates. The U.S. has in fact about the same prostate cancer mortality rate as the U.K. But far more Americans participate in PSA screening (although its effect on mortality reduction has not been proven). As a consequence, more Americans are diagnosed of prostate cancer, which skyrockets the 5-year survival rate to more than 80%, although no life is saved. Screening detects many "silent" prostate cancers that the patient would have never noticed during his lifetime. Americans live longer with the diagnosis, but they do not live longer. Yet many Americans end up incontinent or impotent for the rest of their lives, due to unnecessary aggressive surgery or radiation therapy, believing that their life has been saved.

Giuliani is not an exception to the prevailing confusion about how to evaluate health statistics. For instance, my research shows that 80% to 90% of German physicians do not understand what a positive screening test means — such as PSA, HIV, or mammography — and most do not know how to explain the patient the potential benefits and harms. Patients however falsely assume that their doctors know and understand the relevant medical research. In most medical schools, education in understanding health statistics is currently lacking or ineffective.

The bare fact of statistical illiteracy among physicians, patients, and politicians is still not well known, much less addressed, made me pessimistic about the chances of any improvement. Statistical illiteracy in health matters turns the ideals of informed consent and shared decision-making into science fiction. Yet I have begun to change my mind. Here are a few reasons why I'm more optimistic.

Consider the concept of relative risks. You may have heard that mammography screening reduces breast cancer mortality by 25%! Impressive, isn't it? Many believe that if 100 women participate, the life of 25 will be saved. But don't be taken in again. The number is based on studies that showed that out of every 1,000 women who do not participate in mammography screening, 4 will die of breast cancer within about 10 years, whereas among those who participate in screening this number decreases to 3. This difference can be expressed as anabsolute risk, that is, one out of every 1,000 women dies less of breast cancer, which is a clear and transparent.  But it also can be phrased in terms of a relative risk: a 25% benefit. I have asked hundreds of gynecologists to explain what this benefit figure means. The good news is that two-thirds understood that 25% means 1 in 1,000. Yet one third overestimated the benefits by one or more orders of magnitudes. Thus, better training in medical school is still wanted.

What makes me optimistic is the reaction of some 1,000 gynecologists I have trained in understanding risks and uncertainties as part of their continuing education. First, learning how to communicate risks was a top topic on their wish list. Second, despite the fact that most had little statistical training, they learned quickly. Consider the situation of a woman who tests positive in a screening mammogram, and asks her doctor whether she has cancer for certain, or what her chances are.  She has a right to get the best answer from medical science: Out of ten women who test positive, only one has breast cancer, the other nine cases are false alarms. Most women are never informed about this relevant fact, and react with panic and fear. Mammography is not a very reliable test. Before the training, the majority of gynecologists mistakenly believed that about 9 out of 10 women who test positive have cancer, as opposed to only one! After the training, however, almost all physicians understood how to read this kind of health statistics. That's real progress, and I didn't expect so much, so soon.

What makes me less optimistic is resistance to transparency in health from government institutions. A few years ago, I presented the program of transparent risk communication to the National Cancer Institute in Bethesda. Two officials took me aside afterwards and lauded the program for its potential to make health care more rational. I asked if they intended to implement it. Their answer was no. Why not? As they explained, transparency in this form was bad news for the government — a benefit of only 0.1% instead of 25% would make poor headlines for the upcoming election! In addition, their board was appointed by the presidential administration, for which transparency in health care is not a priority.

Win some, lose some. But I think the tide is turning. Statistics may still be woefully absent from most school curricula, including medical schools. That could soon change in the realm of health, however, if physicians and patients make common cause, eventually forcing politicians to do their homework.

The economist, John Maynard Keynes, when criticised for shifting his position on monetary policy, retorted: "When the facts change, I change my mind. What do you do, sir?" Point taken. Yet, despite the way the Edge 2008 Question has been framed,  in science it is not always true  that it requires new facts to change people's minds.  Instead, as Thomas Kuhn recognised,  at major turning points in the history of science, theorists who have previously found themselves struggling  to make sense of "known facts", sometimes undergo a radical change in perspective, such that they see these same  facts in a quite different light. Where people earlier saw  the rabbit, they  now see the duck.

In my own research on consciousness, I have changed my mind more than once. I expect it will happen again.  But it has not — at least so far  — been because I learned  any new facts. Contrary to the hopes of neuroscientists on one side, quantum physicists on the other, I'm pretty sure all the facts that we need to solve the hard problem are already familiar to us  —   if only we could  see them for what they are. No magic bullet is going to emerge from the lab, from brain imaging or particle accelerators. Instead, what we are waiting for is  merely (!)  a revolutionary new way of thinking about things that we all, as conscious creatures, already know —   perhaps a way of making those same facts unfamiliar. 

What is the hard problem? The problem is to explain the mysterious out-of-this-world qualities of conscious experience —   the felt redness of red, the felt sharpness of pain.  I once believed that  the answer lay in introspection: "thoughts about thoughts", I reckoned, could yield the requisite  magical properties as an emergent property. But I later realised on logical (not factual) grounds that this idea was empty. Magic doesn't simply emerge, it has to be constructed. So, since then, I've been working on a constructivist theory of consciousness. And my most promising line yet (as I see it) has been  to turn the problem round and to imagine that  the hardness of the problem may actually be the key to its solution. 

Just suppose that  the "Cartesian theatre of consciousness", about which modern philosophers are generally so sceptical, is in fact a biological reality. Suppose indeed , that Nature has designed our brains to contain a mental theatre, designed for the very purpose of staging the qualia-rich spectacle on which we set such store. Suppose, in short,  that consciousness exists primarily for our entertainment and amazement. 

I may tell you that, with this changed mind-set, I already see the facts quite differently. I hope it does the same for you, sir.

As a teenager growing up in the rural American Midwest, I played in a Christian rock band. We wrote worship songs, with texts on religious themes, and experienced the jubilation and transport of the music as a visitation by the Holy Spirit. Then one day, as my faith was beginning to waiver, I wrote a song with an explicitly nonreligious theme. To my surprise I discovered that when I performed it, I was overcome by the same feelings, and it dawned on me that maybe what we had experienced all along was our own spirits, that what had called to us was the power of music itself.

In truth, I wasn't thinking through much at the time. Later, as a graduate student of philosophy, I did start to think a lot about science and ethics, and I began to undergo a parallel shift of outlook. Having embraced a thoroughly naturalistic, materialistic worldview, I wondered: If everything is just matter, how could anything really matter? How could values be among the objective furniture of the universe? It is not as if anyone expected physicists to discover, alongside electrons, protons, and neutrons, a new fundamental moral particle--the moron?--which would show up in high magnitudes whenever people did nice things.

Then there was J. L. Mackie's famous argument from "queerness": objective values would have to be such that merely coming to appreciate them would motivate you to pursue them. But given everything we know about how ordinary natural facts behave (they seem to ask nothing of us), how could there possibly be states of affairs with this strange to-be-pursuedness built into them, and how could we come to appreciate them?

At the same time, I was taken in by the promises found in some early sociobiology that a new evolutionary science of human nature would supplant empty talk about objective values. As Michael Ruse once put it, "morality is just an aid to survival and reproduction," and so "any deeper meaning is illusory." Niceness may seem self-evidently right to us, but things could easily have been the other way around, had nastiness paid off more often for our ancestors.

I have since been convinced that I was looking at all of this in the wrong way. Not only are values a part of nature; we couldn't avoid them if we tried.

There is no doubt that had we evolved differently, we would value different things. However, that alone does not show that values are subjective. After all, hearing is accomplished by psychological mechanisms that evolved under natural selection. But it does not follow that the things we hear are any less real. Rather, the reality of the things around us helps to explain why we have the faculty to detect them. The evolved can put us in touch with the objective.

In fact, we are all intimately familiar with entities which are such that to recognize them is to be moved by them. We call them reasons, where a reason is just a consideration that weighs in favor of an action or belief. As separate lines of research by psychologist Daniel Wegner and psychiatrist George Ainslie (as synthesized and interpreted by Daniel Dennett) strongly suggest, our reasons aren't all "in the head," and we cannot help but heed their call.

At some point in our evolution, the behavioral repertoire of our ancestors became complex enough to involve the review and evaluation of numerous possible courses of action and the formation of intentions on the basis of their projected outcomes. In a word, we got options. However, as an ultrasocial species, for whom survival and reproduction depended on close coordination of behaviors over time, we needed to manage these options in a way that could be communicated to our neighbors. That supervisor and communicator of our mental economy is the self, the more-or-less stable "I" that persists through time and feels like it is the author of action. After all, if you want to be able to make reliable threats or credible promises, you need to keep track of who you are, were, and will be. According to this perspective, reasons are a human organism's way of taking responsibility for some of the happenings in its body and environment. As such, they are inherently public and shareable. Reasons are biological adaptations, every bit as real as our hands, eyes, and ears.

I do not expect (and we do not need) a "science of good and evil." However, scientific evidence can show how it is that things matter objectively. I cannot doubt the power of reasons without presupposing the power of reasons (for doubting). That cannot be said for the power of the Holy Spirit.

Russians arrived on the western shores of North America after crossing their Eastern Ocean in 1741. After an initial period of exploration, they settled down for a full century until relinquishing their colonies to the United States. From 1799 to 1867, the colonies were governed by the Russian-American Company, a for-profit monopoly chartered under the deathbed instructions of Catherine the Great.

The Russian-American period has been treated unkindly by historians from both sides. Soviet-era accounts, though acknowledging the skill and courage of Russian adventurers, saw this Tsarist experiment at building a capitalist, American society as fundamentally flawed, casting the native Aleuts as exploited serfs. American accounts, glossing over our own subsequent exploitation of Alaska's indigenous population and natural resources, sought to emphasize that we liberated Alaska from Russian overseers who were worse, and would never be coming back.

Careful study of primary sources has convinced me that these interpretations are not supported by the facts. The Aleutian archipelago was a spectacularly rich environment with an unusually dense, thriving population whose physical and cultural well-being was devastated by contact with European invaders. But, as permanent colonists, the Russians were not so bad. The results were closer to the settlement of Greenland by Denmark than to our own settlement of the American West.

Although during the initial decades leading up to the consolidation of the Russian-American Company there was sporadic conflict (frequently disastrous to the poorly-armed and vastly-outnumbered Russians) with the native population, the colonies soon entered a relatively stable state based on cooperation, intermarriage, and official policies that provided social status, education, and professional training to children of mixed Aleut-Russian birth. Within a generation or two the day-to-day administration of the Russian-American colonies was largely in the hands of native-born Alaskans. As exemplified by the Russian adoption and adaptation of the Aleut kayak, or baidarka, many indigenous traditions and technologies (including sea otter hunting techniques, and the working of native copper deposits) were adopted by the new arrivals, reversing the usual trend in colonization, when indigenous technologies are replaced.

The Russians instituted public education, preservation of the Aleut language through transliteration of religious and other texts into Aleut via an adaptation of the Cyrillic alphabet, vaccination of the native population against smallpox, and science-based sea mammal conservation policies that were far ahead of their time. There were no such things as "reservations" for the native population in Russian America, and we owe as much to the Russians as to the Alaska Native Claims Settlement Act of 1971 that this remains true today.

The lack of support for the colonies by the home government (St. Petersburg was half a world away, and Empress Catherine's instructions a fading memory) eventually forced the sale to the United States, but also necessitated the resourcefulness and local autonomy that made the venture a success.

Russian America was a social and technological experiment that worked, until political compromises brought the experiment to a halt.

In the past few years, I have been thinking and writing about "attention", and specifically, "continuous partial attention". The impetus came from my years of working at Apple, and then, Microsoft, where I thought a lot about user interface as well as our relationship to the tools we create.

I believe that attention is the most powerful tool of the human spirit and that we can enhance or augment our attention with practices like meditation and exercise, diffuse it with technologies like email and Blackberries, or alter it with pharmaceuticals. 

But lately I have observed that the way in which many of us interact with our personal technologies makes it impossible to use this extraordinary tool of attention to our advantage.

In observing others — in their offices, their homes, at cafes — the vast majority of people hold their breath especially when they first begin responding to email. On cell phones, especially when talking and walking, people tend to hyper-ventilate or over-breathe. Either of these breathing patterns disturbs oxygen and CO2 balance.

Research conducted by two NIH scientists, Margaret Chesney and David Anderson, demonstrates that breath holding can contribute significantly to stress-related diseases. The body becomes acidic, the kidneys begin to re-absorb sodium, and as the oxygen and CO2 balance is undermined, our biochemistry is thrown off.

Around this same time, I became very interested in the vagus nerve and the role it played.  The vagus nerve is one of the major cranial nerves, and wanders from the head, to the neck, chest and abdomen.  It's primary job is to mediate the autonomic nervous system, which includes the sympathetic — "fight or flight," and parasympathetic — "rest and digest" nervous systems.   

The parasympathetic nervous system governs our sense of hunger and satiety, flow of saliva and digestive enzymes, the relaxation response, and many aspects of healthy organ function.  Focusing on diaphragmatic breathing enables us to down regulate the sympathetic nervous system, which then causes the parasympathetic nervous system to become dominant.  Shallow breathing, breath holding and hyper-ventilating triggers the sympathetic nervous system, in a "fight or flight" response.

The activated sympathetic nervous system causes the liver to dump glucose and cholesterol into our blood, our heart rate increases, we don't have a sense of satiety, and our bodies anticipate and resource for the physical activity that, historically, accompanied a physical fight or flight response.  Meanwhile, when the only physical activity is sitting and  responding to email, we're sort of "all dressed up with nowhere to go."    

Some breathing patterns favor our body's move toward parasympathetic functions and other breathing  patterns favor a sympathetic nervous system response.  Buteyko (breathing techniques developed by a Russian M.D.), Andy Weil's breathing exercises, diaphragmatic breathing, certain yoga breathing techniques, all have the potential to soothe us, and to help our bodies differentiate when fight or flight is really necessary and when we can rest and digest. 

I've changed my mind about how much attention to pay to my breathing patterns and how important it is to remember to breathe when I'm using a computer, PDA or cell phone. 

I've discovered that the more consistently I tune in to healthy breathing patterns, the clearer it is to me when I'm hungry or not, the more easily I fall asleep and rest peacefully at night, and the more my outlook is consistently positive. 

I've come to believe that, within the next 5-7 years, breathing exercises will be a significant part of any fitness regime.

Imagine me, if you will, in the Oxford of 1970; a new undergraduate, thrilled by the intellectual atmosphere, the hippy clothes, joss-stick filled rooms, late nights, early morning lectures, and mind-opening cannabis. 

I joined the Society for Psychical Research and became fascinated with occultism, mediumship and the paranormal — ideas that clashed tantalisingly with the physiology and psychology I was studying. Then late one night something very strange happened. I was sitting around with friends, smoking, listening to music, and enjoying the vivid imagery of rushing down a dark tunnel towards a bright light, when my friend spoke. I couldn't reply.

"Where are you Sue?" he asked, and suddenly I seemed to be on the ceiling looking down.

"Astral projection!" I thought and then I (or some imagined flying "I") set off across Oxford, over the country, and way beyond. For more than two hours I fell through strange scenes and mystical states, losing space and time, and ultimately my self. It was an extraordinary and life-changing experience. Everything seemed brighter, more real, and more meaningful than anything in ordinary life, and I longed to understand it.

But I jumped to all the wrong conclusions. Perhaps understandably, I assumed that my spirit had left my body and that this proved all manner of things — life after death, telepathy, clairvoyance, and much, much more. I decided, with splendid, youthful over-confidence, to become a parapsychologist and prove all my closed-minded science lecturers wrong. I found a PhD place, funded myself by teaching, and began to test my memory theory of ESP. And this is where my change of mind — and heart, and everything else — came about.

I did the experiments. I tested telepathy, precognition, and clairvoyance; I got only chance results. I trained fellow students in imagery techniques and tested them again; chance results. I tested twins in pairs; chance results. I worked in play groups and nursery schools with very young children (their naturally telepathic minds are not yet warped by education, you see); chance results. I trained as a Tarot reader and tested the readings; chance results.

Occasionally I got a significant result. Oh the excitement! I responded as I think any scientist should, by checking for errors, recalculating the statistics, and repeating the experiments. But every time I either found the error responsible, or failed to repeat the results. When my enthusiasm waned, or I began to doubt my original beliefs, there was always another corner to turn — always someone saying "But you must try xxx". It was probably three or four years before I ran out of xxxs.

I remember the very moment when something snapped (or should I say "I seem to …" in case it's a false flash-bulb memory). I was lying in the bath trying to fit my latest null results into paranormal theory, when it occurred to me for the very first time that I might have been completely wrong, and my tutors right. Perhaps there were no paranormal phenomena at all.

As far as I can remember, this scary thought took some time to sink in. I did more experiments, and got more chance results. Parapsychologists called me a "psi-inhibitory experimenter", meaning that I didn't get paranormal results because I didn't believe strongly enough. I studied other people's results and found more errors and even outright fraud. By the time my PhD was completed, I had become a sceptic.

Until then, my whole identity had been bound up with the paranormal. I had shunned a sensible PhD place, and ruined my chances of a career in academia (as my tutor at Oxford liked to say). I had hunted ghosts and poltergeists, trained as a witch, attended spiritualist churches, and stared into crystal balls. But all of that had to go.

Once the decision was made it was actually quite easy. Like many big changes in life this one was terrifying in prospect but easy in retrospect. I soon became "rentasceptic", appearing on TV shows to explain how the illusions work, why there is no telepathy, and how to explain near-death experiences by events in the brain.

What remains now is a kind of openness to evidence. However firmly I believe in some theory (on consciousness, memes or whatever); however closely I might be identified with some position or claim, I know that the world won't fall apart if I have to change my mind.

I've changed my mind about how to handle the homunculus temptation: the almost irresistible urge to install a "little man in the brain" to be the Boss, the Central Meaner, the Enjoyer of pleasures and the Sufferer of pains. In Brainstorms (1978) I described and defended the classic GOFAI (Good Old Fashioned AI) strategy that came to be known as "homuncular functionalism," replacing the little man with a committee.

The AI programmer begins with an intentionally characterized problem, and thus frankly views the computer anthropomorphically: if he solves the problem he will say he has designed a computer than can [e.g.,] understand questions in English . His first and highest level of design breaks the computer down into subsystems, each of which is given intentionally characterized tasks; he composes a flow chart of evaluators, rememberers, discriminators, overseers and the like. These are homunculi with a vengeance. . . . . Each homunculus in turn is analyzed into smaller homunculi, but, more important, into less clever homunculi. When the level is reached where the homunculi are no more than adders and subtractors, by the time they need only the intelligence to pick the larger of two numbers when directed to, they have been reduced to functionaries "who can be replaced by a machine." (p80)

I still think that this is basically right, but I have recently come to regret–and reject–some of the connotations of two of the terms I used: committee and machine. The cooperative bureaucracy suggested by the former, with its clear reporting relationships (an image enhanced by the no-nonsense flow charts of classical cognitive science models) was fine for the sorts of computer hardware–and also the levels of software, the virtual machines–that embodied GOFAI, but it suggested a sort of efficiency that was profoundly unbiological. And while I am still happy to insist that an individual neuron, like those adders and subtractors in the silicon computer, "can be replaced by a machine," neurons are bio-machines profoundly unlike computer components in several regards.

Notice that computers have been designed to keep needs and job performance almost entirely independent. Down in the hardware, the electric power is doled out evenhandedly and abundantly; no circuit risks starving. At the software level, a benevolent scheduler doles out machine cycles to whatever process has highest priority, and although there may be a bidding mechanism of one sort or another that determines which processes get priority, this is an orderly queue, not a struggle for life. (As Marx would have it, "from each according to his abilities, to each according to his needs). It is a dim appreciation of this fact that probably underlies the common folk intuition that a computer could never "care" about anything. Not because it is made out of the wrong materials — why should silicon be any less suitable a substrate for caring than organic molecules? — but because its internal economy has no built-in risks or opportunities, so it doesn't have to care.

Neurons, I have come to believe, are not like this. My mistake was that I had stopped the finite regress of homunculi at least one step too early! The general run of the cells that compose our bodies are probably just willing slaves–rather like the selfless, sterile worker ants in a colony, doing stereotypic jobs and living out their lives in a relatively non-competitive ("Marxist") environment. But brain cells — I now think — must compete vigorously in a marketplace. For what?

What could a neuron "want"? The energy and raw materials it needs to thrive–just like its unicellular eukaryote ancestors and more distant cousins, the bacteria and archaea. Neurons are robots; they are certainly not conscious in any rich sense–remember, they are eukaryotic cells, akin to yeast cells or fungi. If individual neurons are conscious then so is athlete’s foot. But neurons are, like these mindless but intentional cousins, highly competent agents in a life-or-death struggle, not in the environment between your toes, but in the demanding environment of the brain, where the victories go to those cells that can network more effectively, contribute to more influential trends at the virtual machine levels where large-scale human purposes and urges are discernible.

I now think, then, that the opponent-process dynamics of emotions, and the roles they play in controlling our minds, is underpinned by an "economy" of neurochemistry that harnesses the competitive talents of individual neurons. (Note that the idea is that neurons are still good team players within the larger economy, unlike the more radically selfish cancer cells. Recalling Francois Jacob’s dictum that the dream of every cell is to become two cells, neurons vie to stay active and to be influential, but do not dream of multiplying.)

Intelligent control of an animal’s behavior is still a computational process, but the neurons are "selfish neurons," as Sebastian Seung has said, striving to maximize their intake of the different currencies of reward we have found in the brain. And what do neurons "buy" with their dopamine, their serotonin or oxytocin, etc.? Greater influence in the networks in which they participate.

I am a heretic. I have come to question the key assumption behind this survey: "When facts change your mind, that's science." This idea that science is an objective fact-driven pursuit is laudable, seductive and - alas - a mirage.

Science is a never-ending dialogue between theorists and experimenters. But people are central to that dialogue. And people ignore facts. They distort them or select the ones that suit their cause, depending on how they interpret their meaning. Or they don't ask the right questions to obtain the relevant facts.

Contrary to the myth of the ugly fact that can topple a beautiful theory - and against the grain of our lofty expectations - scientists sometimes play fast and loose with data, highlighting what that suits them and ignoring stuff that doesn't.

The harsh spotlight of the media often encourages them to strike a confident pose even if the facts don't. I am often struck by how facts are ignored, insufficient or even abused. I back well-designed animal research but am puzzled by how scientists chose to ignore the basic fact that vivisection is so inefficient at generating cures for human disease. Intelligent design is for cretins but, despite the endless proselytizing about the success of Darwin - assuming that evolution is a fact - I could still see it being superseded, rather as Einstein's ideas replaced Newton's law of gravity. I believe in man-made global warming but computer-projected facts that purportedly say what is in store for the Earth in the next century leave me cold.

I support embryo research but was irritated by one oft-cited fact in the recent British debate on the manufacture of animal-human hybrid embryos: "only a tiny fraction" of the hybrid made by the Dolly cloning method (nuclear transfer) contains animal DNA. Given that it features in mitochondria, which are central to a range of diseases; given a single spelling mistake in DNA can be catastrophic; and given no-one really understands what nuclear transfer does, this "fact" was propaganda.

Some of the most exotic and prestigious parts of modern science are unfettered by facts. I have recently written about whether our very ability to study the heavens may have shortened the inferred lifetime of the cosmos, whether there are two dimensions of time, even the prospect that time itself could cease to be in billions of years. The field of cosmology is in desperate need of more facts, as highlighted by the aphorisms made at its expense ("There is speculation, pure speculation and cosmology.... cosmologists are often in error, never in doubt')

Scientists have to make judgements about the merits of new facts. Ignoring them in the light of strong intuition is the mark of a great scientist. Take Einstein, for example: when Kaufmann claimed to have experimental facts that refuted special relativity, he stuck to his guns and was proved right. Equally, Einstein's intuition misled him in his last three decades, when he pursued a fruitless quest for a unified field theory that was not helped by his lack of interest in novel facts - the new theoretical ideas, particles and interactions that had emerged at this time.

When it comes to work in progress, in particular, many scientists treat science like a religion - the facts should be made to fit the creed. However, facts are necessary for science but not sufficient. Science is when, in the face of extreme scepticism, enough facts accrue to change lots of minds.

Our rising and now excessive faith in facts alone can be seen in a change in the translation of the motto of the world's oldest academy of science, the Royal Society. Nullius in Verba was once taken as 'on the word of no one' to highlight the extraordinary power that empirical evidence bestowed upon science. The message was that experimental evidence trumped personal authority.

Today the Society talks of the need to 'verify all statements by an appeal to facts determined by experiment'. But whose facts? Was it a well-designed experiment? And are we getting all the relevant facts? The Society should adopt the snappier version that captures its original spirit: 'Take nobody's word for it'.

Edge’s question this year wittily refers to a way of demarcating science from philosophy and religion.  “When thinking changes your mind, that’s philosophy . . . .  When facts change your mind, that’s science.” Behind the witticism lies the important claim that science—or more precisely, scientific theories—can be clearly distinguished from all other theories, that scientific theories bear a special mark, and what this mark is is falsifiability. Said Popper:  The criterion of the scientific status of a theory is its falsifiability.  

For most scientists, this is all they need to know about the philosophy of science. It was bracing to come upon such a clear and precise criterion for identifying  scientific theories. And it was gratifying to see how Popper used it to discredit the claims that  psychoanalysis and Marxism are scientific theories. It had long seemed to me that the falsifiability test was basically right and enormously useful.

But then I started to read Popper’s work carefully, to teach him in my philosophy of science classes, and to look to scientific practice to see whether his theory survives the test of falsifiability (at least as a description of how successful science gets done). And I’ve changed my mind.

For one thing, Popper’s characterization of how science is practiced—as a cycle of conjecture and refutation—bears little relation to what goes on in the labs and journals. He describes science as if it was skeet-shooting, as if the only goal of science is to prove that one theory after another is false. But just open a copy of Science.  To pick a random example: “In a probabilistic learning task, A1-allele carriers with reduced dopamine D2 receptor densities learned to avoid actions with negative consequences less efficiently.” Not, “We tried to falsify the hypothesis that A1 carriers are less efficient learners, and failed.” Scientists rarely write the way that Popper says they should, and a good Popperian should recognize that the Master may have over-simplified the logic of theory testing.

Also, scientists don’t, and shouldn’t, jettison a theory as soon as a disconfirming datum comes in. As Francis Crick once said, “Any theory that can account for all of the facts is wrong, because some of the facts are always wrong.” Scientists rightly question a datum that appears to falsify an elegant and well-supported theory, and they rightly add assumptions and qualifications and complications to a theory as they learn more about the world. As Imre Lakatos, a less-cited (but more subtle) philosopher of science points out, all scientific theories are unfalsifiable. The ones we take seriously are those that lead to “progressive” research programs, where a small change accommodates a large swath of past and future data. And the ones we abandon are those that lead to “degenerate” ones, where the theory gets patched and re-patched at the same rate as new facts come in.

Another problem with the falsifiability criterion is that I have seen it  become a blunt instrument, unthinkingly applied. Popper tried to use it to discredit not only Marxism and Freudianism as scientific theories but also Darwin’s theory of natural selection—a position that only a creationist could hold today. I have seen scientists claim that major theories in contemporary cosmology and physics are not “science” because they can’t think of a simple test that would falsify them. You’d think that when they are faced with a conflict between what scientists really do and their memorized Popperian sound-bite about how science ought to be done, they might question the sound bite, and go back and learn more than a single sentence from the philosophy of science. But such is the godlike authority of Popper that his is the one theory that can never be falsified!

Finally, I’ve come to think that identifying scientificality with falsifiability lets certain non-scientific theories off the hook, by saying that we should try to find good reasons to believe whether a theory is true or false only when that theory is called “science.” It allows believers to protect their pet theories by saying that they can’t be, and shouldn’t be, subject to falsification, just because they’re clearly not scientific theories. Take the theory that there’s an omnipotent, omniscient, beneficent God. It may not be a scientific hypothesis, but it seems to me to be eminently falsifiable; in fact, it seems to have been amply falsified.   But because falsifiability is seen as demarcating the scientific, and since theism is so clearly not scientific, believers in religious ideologies get a free pass. The same is true for many political ideologies. The parity between scientific and nonscientific ideas is concealed by thinking that there’s a simple test that distinguishes science from nonscience, and that that test is falsifiability.

We do not so much change our minds about facts, although we necessarily correct and rearrange them in changing contexts. But we do change our minds about the significance of those facts.

I can remember, as a young woman, first grasping the danger of environmental destruction at a conference in 1968.  The context was the intricate interconnection within all living systems, a concept that applied to ecosystems like forests and tide pools and equally well to human communities and to the planet as a whole, the sense of an extraordinary interweaving of life, beautiful and fragile, and threatened by human hubris. It was at that conference also that I first heard of the greenhouse effect, the mechanism that underlies global warming. A few years later, however, I heard of the Gaia Hypothesis (proposed by James Lovelock in 1970), which proposed that the same systemic interconnectivity gives the planet its resilience and a capacity for self correction that might survive human tampering. Some environmentalists welcomed the Gaia hypothesis, while others warned that it might lead to complacency in the face of real and present danger. With each passing year, our knowledge of how things are connected is enriched but the significance of these observations is still debated.

J.B.S. Haldane was asked once what the natural world suggested about the mind of its Creator, and he replied "an inordinate fondness for beetles." This observation also plays differently for different listeners—a delight in diversity, perhaps, as if the Creator might have spent the first sabbath afternoon resting from his work by playfully exploring the possible ramifications of a single idea (beetles make up roughly one fifth of all known species on the planet, some 350,000 of them)—or a humbling (or humiliating?) lack of preoccupation with our own unique kind, which might prove to be a temporary afterthought, survived only by cockroaches.

These two ways of looking at what we observe seem to recur, like the glass half full and the glass half empty.  The more we know of the detail of living systems, the more we seem torn between anxiety and denial on the one hand and wonder and delight on the other as we try to understand the significance of our knowledge. Science has radically altered our awareness of the scale and age of the universe, but this changing awareness seems to stimulate humility in some—our planet a tiny speck dominated by flea-like bipeds—and a sort of megalomania in others who see all of this as directed toward us, our species, as its predestined masters. Similarly, the exploration of human diversity in the twentieth century expanded for some the sense of plasticity and variability and for others reinforced the sense of human unity. Even within these divergent emphases, for some the recognition of human unity includes a capacity for mutual recognition and adaptation while for others it suggests innate tendencies toward violence and xenophobia. As we have slowly explored the mechanisms of memory and learning, we have seen examples of (fragile) human communities demoralized by exposure to other cultures and (resilient) examples of extraordinary adaptability. At one moment humans are depicted as potential stewards of the biosphere, at another as a cancer or a dangerous infestation. The growing awareness of a shared and interconnected destiny has a shadow side, the version of globalization that looks primarily for profit.

We are having much the same sort of debate at present between those who see religion primarily as a source of conflict between groups and others who see the world's religions as potentially convergent systems that have knit peoples together and laid the groundwork for contemporary ideas of human rights and civil society. Some believers feel called to treasure and respect the creation, including the many human cultures that have grown within it, while others regard differences of belief as sinful and the world we know as transitory or illusory. Each of the great religions, with different language and different emphases, offers the basis for environmental responsibility and for peaceful coexistence and compassion, but believers differ in what they choose to emphasize, all too many choosing the apocalyptic over the ethical texts. Nevertheless, major shifts have been occurring in the interpretation of information about climate change, most recently within the evangelical Christian community.   

My guess is that many people have tilted first one way and then the other over the past fifty years, as we have become increasingly aware of diverse understandings—surprised by accounts of human creativity and adaptation on the one hand, and distressed at the resurgence of ancient quarrels and loss of tolerance and mutual respect. Some people are growing away from irresponsible consumerism while others are having their first taste of affluence. Responses are probably partly based on temperament—generalized optimism vs. pessimism—so the tension will not be resolved by scientific findings. But these responses are also based on the decisions we make, on making up our minds about which interpretations we choose to believe. The world's historic religions deal in different ways with loss and the need for sacrifice, but the materials are there for working together, just as they are there for stoking conflict and competition.  We are most likely to survive this century if we decide to approach the choices and potential losses ahead with an awareness of the risks we face but at the same time with an awareness of the natural wonders around us and a determination to deal with each other with respect and faith in the possibility of cooperation and responsibility.
 

As a young graduate student in operations research I was avid believer in the power of scientific modelling. How wrong I was. Often, modelling is searching for a coin under the light of science, and not where it is.

First, all models have certain degree of approximation. Second, at least in operations research, human factors,errors, randomness, unexpected developments, social behaviors, human errors all are influencing the results, or are not accounted for in the modelling. In time I become more skeptical and doubtful.

It helps if you can maintain your sense of humor. In the end, it is not about the data or the changes in the data, but how you see it, and how much you believe in it.

I've changed my mind about electronic mail. When I first used email in graduate school in 1980, it was a dream. It was the most marvelous and practical invention of computer science. A text message quickly typed and reliably delivered (or be told of an error) allowed a new kind of asynchronous communication. It was cheaper (free), faster, and much more efficient than mail, phone, or fax, with a roundtrip in minutes. Only your colleagues had your address, but you could find people at other places using "finger". Colleagues started sharing text-formatted data tables, where 50K bytes was a big email message!

Then came attachments. This hack to insert 33% bloated 8-bit binary files inside of 7-bit text email opened a Pandora's box. Suddenly anyone had the right to send any size package for FREE, like a Socialized United Parcel Service. Microsoft Outlook made it "drag 'n drop" easy for bureaucrats to send word documents. Many computer scientists saw the future and screamed "JUST SEND TEXT" but it was too late. Microsoft kept tweaking its proprietary file formats forcing anyone with email to upgrade Microsoft Office. (I thought they finally stopped with Office 97, but now I am getting DOC-X-files, which might as well be in Martian!)

We faced AOL newbies, mailing lists, free webmail, hotmail spam, RTF mail, chain letters, html mail, musical mail, flash mail, javascript mail, viruses, spybits, faked URL's, phishing, Nigerian cons, Powerpoint arms races, spam-blocking spam, viral videos, Plaxo updates, Facebook friendings, ad nauseum.

The worst part is the legal precedent that your employer "owns" the mail sent out over the network provided. It is as if they own the soundwaves which emit from your throat over the phone. An idiot judgment leads to two Kafkaesque absurdities:

First, if you send email with an ethnic slur, receive email with a picture of a naked child or a copyrghted MP3, you can be fired. Use email to organize a Union? Fugget about it! Second, all email sent and received must now be archived as critical business documents to comply with Sarbanes Oxley. And Homeland Security wants rights to monitor ISP data streams and stores, and hope no warrants are needed for data older than 90 days.

Free Speech in the Information Age isn't your right to post anonymously on a soapbox blog or newspaper story. It means that, if we agree, I should be able to send any data in any file format, with any encryption, from a computer I am using to one your are on, provided we pay for the broadband freight. There is no reason that any government, carrier, or corporation should have any right to store, read, or interpret our digital communications. Show just cause and get a warrant, even if you think an employee is spying or a student is pirating music.

Email is now a nightmare that we have to wake up from. I don't have a solution yet, but I believe the key to re-imagine email is to realize that our computers and phones are "always on" the net. So we can begin with synchronous messaging (both sender and receiver are online) — a cross between file sharing, SMS texting, and instant messaging — and then add grid storage mechanisms for asynchronous delivery, multiple recipients, and reliability.

Until then, call me.

Richard Feynman held that philosophy of science is as useful to scientists as ornithology is to birds. Often this is so. But the unavoidable question about physics is — where do the laws come from?

Einstein hoped that God had no choice in making the universe. But philosophical issues seem unavoidable when we hear of  the "landscape" of possible string theory models. As now conjectured, the theory leads to 10500 solution universes — a horrid violation of Occam's Razor we might term "Einstein's nightmare."

I once thought that the laws of our universe were unquestionable, in that there was no way for science to address the question. Now I'm not so sure. Can we hope to construct a model of how laws themselves arise?

Many scientists dislike even the idea of doing this, perhaps because it's hard to know where to start. Perhaps ideas from the currently chic technology, computers, are a place to start. Suppose we treat the universe as a substrate carrying out computations, a meta-computer.

Suppose that precise laws require computation, which can never be infinitely exact. Such a limitation that might be explained by counting the computational capacity of a sphere around an "experiment" that tries to measure outcomes of those laws. The sphere expands at the speed of light, say, so longer experiment times give greater precision. Thinking mathematically, this sets a limit on how sharp differentials can be in our equations. A partial derivative of time cannot be better than the time to compute it.

In a sense, there may be an ultimate limit on how well known any law can be, especially one that must describe all of space-time, like classical relativity. It can't be better than the total computational capacity of the universe, or the capacity within the light sphere we can see.

I wonder if this idea can somehow define the nature of laws, beyond the issue of their precision? For example, laws with higher derivatives will be less descriptive because their operations cannot be carried out in a given volume over a finite time.

Perhaps the infinite discreteness required for formulating any mathematical system could be the limiting bound on such discussions. There should be energy bounds, too, within a finite volume, and thus limits on processing power set by the laws of thermodynamics. Still, I don't see how these arguments tell us enough to derive, say, general relativity.

Perhaps we need more ideas to derive a Law of Laws. Can we use the ideas of evolution? Perhaps invoke selection among laws that penalize those laws that lead to singularities — and thus taking those regions of space-time out of the game? Lee Smolin tried a limited form of this by supposing universes reproduce through black hole collapses. Ingenious, but that didn't seem to lead very far. He imagined some variation in reproduction of budded-off generations of universes, so their fundamental parameters varied a bit. Then selection could work.

In a novel of a decade ago, Cosmo, I invoked intelligent life, rather than singularities, to determine selection for universes that can foster intelligence, as ours seems to. (I didn't know about Lee's ideas at the time.) The idea is that a universe hosting intelligence evolves creatures that find ways in the laboratory to make more universes, which bud off and can further engender more intelligence, and thus more experiments that make more universes. This avoids the problem of how the first universe started, of course. Maybe the Law of Laws could answer that, too?

I have more many years worked on pattern in the developing embryo formation which is the development of spatial organization as seen, for example in the arm and hand. My main model for pattern formation is based on cells acquiring a positional value. The model proposes that cells have their position specified as in a co-ordinate system and this determines, depending on their developmental history and their genetic constitution what they do.

The development of the chick limb illustrates some of the problems. As the wing grows out from the flank up there is a thickened ridge of the covering sheet of cells that secretes special proteins which we think, and this is controversial, specifies a region in the cells beneath the ridge which we call the progress zone. At the posterior margin of the limb is the polarising region which secretes a protein, Sonic Hedgehog. This is a signaling molecule used again and again in the development of the embryo. The normal pattern of digits in the chick wing is 2, 3, and 4. If another polarising region is grafted to the anterior margin the pattern of digits is 4, 3, 2, 2, 3, 4.

The interpretation is that Sonic Hedgehog sets up a gradient which specifies position and with the graft there is a mirror image gradient and Crick suggested this was due to diffusion of a molecule like sonic hedgehog setting up a gradient. We have worked hard to show that this model is correct.

The best evidence that it maybe gradient is that if just a small amount of Sonic Hedgehog in the anterior margin then you just get an extra digit 2. If one increases it a bit put a little bit more and you get a 3, 2. But is there really a diffusible gradient in Sonic Hedgehog specifying position? The situation is much more complex.

We now think that the model is wrong as diffusion of a molecule is far too unreliable for reliably and accurately specifying positional values. The reasons why we think diffusion cannot work is that there is now good evidence that a diffusing molecule has to go between and even into cells, and interact with extracellular molecules making it totally unreliable. A more attractive model might be based on interactions at cell contacts as in the polarity models proposed by others. Position would be specified by cells talking to each other. 

This is a serious change in my thinking.

When I began my career as a forecaster over two decades ago, it was a given that the core of futures research lay beyond the reach of traditional quantitative forecasting and it's mathematical tools.  This meant that futures researchers would not enjoy the full labor-saving benefits of number-crunching computers, but at least it guaranteed job security.  Economists and financial analysts might one day wake up to discover that their computer tools were stealing their jobs, but futurists would not see machines muscling their way into the world of qualitative forecasting anytime soon.

I was mistaken.  I now believe that in the not too distant future, the best forecasters will not be people, but machines: ever more capable "prediction engines" probing ever deeper into stochastic spaces.  Indicators of this trend are everywhere from the rise of quantitative analysis in the financial sector, to the emergence of computer-based horizon scanning systems in use by governments around the world, and of course the relentless advance of computer systems along the upward-sweeping curve of Moore's Law.

We already have human-computer hybrids at work in the discovery/forecasting space, from Amazon's Mechanical Turk, to the myriad online prediction markets.  In time, we will recognize that these systems are an intermediate step towards prediction engines in much the same way that human "computers" who once performed the mathematical calculations on complex projects were replaced by general-purpose electronic digital computers.

The eventual appearance of prediction engines will also be enabled by the steady uploading of reality into cyberspace, from the growth of web-based social activities to the steady accretion of sensor data sucked up by an exponentially growing number of devices observing and increasingly, manipulating the physical world.  The result is an unimaginably vast corpus of raw material, grist for the prediction engines as they sift and sort and peer ahead.  These prediction engines won't ever exhibit perfect foresight, but as they and the underlying data they work on co-evolve, it is a sure bet that they will do far better then mere humans.

I was once a devout member of the Church of Evolutionary Psychology.

I believed in modules — lots of them. I believed that the mind could be thought of as a confederation of hundreds, possibly thousands, of information-processing neural adaptations. I believed that each of these mental modules had been fashioned by the relentless winnowing of natural selection as a solution to problems encountered by our hunter-gatherer ancestors in the Pleistocene. I believe I actually said that we were living in the Space Age with brains from the Stone Age. Which was clever — but not, it turned out, particularly wise.

Along with the Church Elders, I believed that this was our universal evolutionary heritage; that if you added together a whole host of these
domain-specific mini-computers — a face recognition module, a spatial relations module, a rigid object mechanics module, a tool-use module, a social exchange module, a child-care module, a kin-oriented motivation module, a sexual attraction module, a grammar acquisition module and so on —  then you had the neurocognitive architecture that comprises the human mind. Along with them, I believed that what made the human mind special was not fewer of these 'instincts', but more of them.

I was so enchanted by this view of life that I used it as the conceptual scaffolding upon which to build a multi-million dollar critically- acclaimed PBS series that I created and hosted in 1996.

And then I changed my mind.

Actually, I prefer to say that I experienced a conversion. My
conversion — literally, the turning around — the adoption of new beliefs was prompted primarily by conversations. First and foremost with an apostate from the Church of Evolutionary Psychology's inner sanctum (Peggy La Cerra); then with a group of colleagues including neuroscientists, evolutionary biologists and philosophers. Two years later, La Cerra and I published in PNAS an alternative model of the mind and followed that with a book in 2002.

Although this is not the place to detail the arguments, we suggested that the selective pressures of navigating ancestral environments — particularly the social world — would have required an adaptively flexible, on-line information-processing system and would have driven the evolution of the neocortex.  We claimed that the ultimate function of the mind is to devise behavior that wards off the depredations of entropy and keeps our energy bank balance in the black. So our universal evolutionary heritage is not a bundle of instincts, but a self-adapting system that is responsive to environmental stimuli, constantly analyzing bioenergetic costs and benefits, creating a customized database of experiences and outcomes, and generating minds that are unique by design.     

We also explained the construction of selves, how our systems adapt to different 'marketplaces', and the importance of reputation effects — a richly nuanced story, which explains why the phrase "I changed my mind" is, with all due respect, the kind of rather simplistic folk psychological language that I hope we will eventually clean up. I think it was Mallarmé who said it was the duty of the poet to purify the language of the tribe. That task now falls also to the scientist.

This model of the mind that I have now subscribed to for about a decade is the bible at the Church of Theoretical Evolutionary Neuroscience (of which I am a co-founder). It was created in alignment with both the adaptationist principles of evolutionary biologists and psychologists (who, at the time, tended to pay little attention to the actual workings of the brain at the implementation level of neurons) and the constructivist principles of neuroscientists (who tended to pay little attention to adaptationism). It would be unrealistic, however, to claim that the two perspectives have yet been satisfactorily reconciled. 

And this time, I am not so devout.

Some Evolutionary Psychologists promoted their ideas with a fervor that has been described as evangelical. To a certain extent, that seems to go with the evolutionary territory: think of the ideological feuds surrounding sociobiology, the renewed debates about levels of selection and so on. Of course, it could be argued that the latest subfields of neuroscience (like neuroeconomics and social cognitive neuroscience) are not immune to these enthusiasms (the word comes from the Greekenthousiasmos: inspired or possessed by a god or gods). Think of the fMRI-mediated  neophrenological explosion of areas said to be the neural correlate of some characteristic or other; or whether the mirror neuron system can possibly carry all the conceptual freight currently being assigned to it.

Even in science, a seductive story will sometimes, at least for a while, outpace the data. Maybe that's inevitable in the pioneering phase of a fledgling discipline. But that's when caution is most necessary — when the engine of discovery is running more on faith than facts. That's the time to remember that hubris is a sin in science as well as religion.

I have changed my mind about using the sample mean as the best way to combine measurements into a single predictive value.  Sometimes it is the best way to combine data but in general you do not know that in advance.  So it is not the one number from or about a data set that I would want to know in the face of total uncertainty if my life depended on the predicted outcome.

Using the sample mean always seemed like the natural thing to do.  Just add up the numerical data and divide by the number of data.  I do not recall ever doubting that procedure until my college years.  Even then I kept running into the mean in science classes and even in philosophy classes where the discussion of ethics sometimes revolved around Aristotle's theory of the "golden mean." There were occasional mentions of medians and modes and other measures of central tendency but they were only occasional.      

The sample mean also kept emerging as the optimal way to combine data in many formal settings.  At least it did given what appeared to be the reasonable criterion of minimizing the squared errors of the observations.  The sample mean falls out from just one quick application of the differential calculus.  So the sample mean had on its side not only mathematical proof and the resulting prominence of appearing in hundreds if not thousands of textbooks and journal articles.  It was and remains the evidentiary workhorse of modern applied science and engineering.  The sample mean summarizes test scores and gets plotted in trend lines and centers confidence intervals among numerous other applications.

Then I ran into the counter-example of Cauchy data.  These data come from bell curves with tails just slightly thicker than the familiar "normal" bell curve.  Cauchy bell curves also describe "normal" events that correspond to the main bell of the curves.  But Cauchy bell curves have thicker tails than normal bell curves have and these thicker tails allow for many more "outliers" or rare events.  And Cauchy bell curves arise in a variety of real and theoretical cases.  The counter-example is that the sample mean of Cauchy data does not improve no matter how many samples you combine.  This result contrasts with the usual result from sampling theory that the variance of the sample mean falls with each new measurement and hence predictive accuracy improves with sample size (assuming that the square-based variance term measures dispersion and that such a mathematical construct always produces a finite value — which it need not produce in general).  The sample mean of ten thousand Cauchy data points has no more predictive power than does the sample mean of ten such data points.  Indeed the sample mean of Cauchy data has no more predictive power than does any one of the data points picked at random.  This counter-example is but one of the anomalous effects that arise from averaging data from many real-world probability curves that deviate from the normal bell curve or from the twenty or so other closed-form probability curves that have found there way into the literature in the last century.

Nor have scientists always used the sample mean.  Historians of mathematics have pointed to the late sixteenth century and the introduction of the decimal system for the start of the modern practice of computing the sample mean of data sets to estimate typical parameters.  Before then the mean apparently meant the arithmetic average of just two numbers as it did with Aristotle.  So Hernan Cortes may well have had a clear idea about the typical height of an adult male Aztec in the early sixteenth century.  But he quite likely did not arrive at his estimate of the typical height by adding measured heights of Aztec males and then dividing by the number added.  We have no reason to believe that Cortes would have resorted to such a computation if the Church or King Charles had pressed him to justify his estimate.  He might just as well have lined up a large number of Aztec adult males from shortest to tallest and then reported the height of the one in the middle.

There was a related and deeper problem with the sample mean:  It is not robust.  Extremely small or large values distort it.  This rotten-apple property stems from working not with measurement errors but with squared errors.  The squaring operation exaggerates extreme data even though it greatly simplifies the calculus when trying to find the estimate that minimizes the observed errors.  That estimate turns out to be the sample mean but not in general if one works with the raw error itself or other measures.  The statistical surprise of sorts is that using the raw or absolute error of the data gives the sample median as the optimal estimate.

The sample median is robust against outliers.  If you throw away the largest and smallest values in a data set then the median does not change but the sample mean does (and gives a more robust "trimmed" mean as used in combining the judging scores in figure skating and elsewhere to remove judging bias).  Realtors have long since stated typical housing prices as sample medians rather than sample means because a few mansions can so easily skew the sample mean.  The sample median would not change even if the price of the most expensive house rose to infinity.  The median would still be the middle-ranked house if the number of houses were odd.  But this robustness is not a free lunch.  It comes at the cost of ignoring some of the information in the numerical magnitudes of the data and has its own complexities for multidimensional data.

Other evidence pointed to using the sample median rather than the sample mean.  Statisticians have computed the so-called breakdown point of these and other statistical measures of central tendency.  The breakdown point measures the largest proportion of data outliers that a statistic can endure before it breaks down in a formal sense of producing very large deviations.  The sample median achieves the theoretical maximum breakdown point.  The sample mean does not come close.  The sample median also turns out to be the optimal estimate for certain types of data (such as Laplacian data) found in many problems of image processing and elsewhere — if the criterion is maximizing the probability or likelihood of the observed data.  And the sample median can also center confidence intervals.  So it too gives rises to hypothesis tests and does so while making fewer assumptions about the data than the sample mean often requires for the same task. 

The clincher was the increasing use of adaptive or neural-type algorithms in engineering and especially in signal processing.  These algorithms cancel echoes and noise on phone lines as well as steer antennas and dampen vibrations in control systems.  The whole point of using an adaptive algorithm is that the engineer cannot reasonably foresee all the statistical patterns of noise and signals that will bombard the system over its lifetime.  No type of lifetime average will give the kind of performance that real-time adaptation will give if the adaptive algorithm is sufficiently sensitive and responsive to its measured environment.  The trouble is that most of the standard adaptive algorithms derive from the same old and non-robust assumptions about minimizing squared errors and thus they result in the use of sample means or related non-robust quantities.  So real-world gusts of data wind tend to destabilize them.  That is a high price to pay just because in effect it makes nineteenth-century calculus computations easy and because such easy computations still hold sway in so much of the engineering curriculum.  It is an unreasonably high price to pay in many cases where a comparable robust median-based system or its kin both avoids such destabilization and performs similarly in good data weather and does so for only a slightly higher computational cost.  There is a growing trend toward using robust algorithms.  But engineers still have launched thousands of these non-robust adaptive systems into the stream of commerce in recent years.  We do not know whether the social costs involved from using these non-robust algorithms are negligible or substantial.

So if under total uncertainty I had to pick a predictive number from a set of measured data and if my life depended on it — I would now pick the median.

Like many or perhaps most I wanted to believe that our oceans and atmosphere were basically unlimited sinks with an endless capacity to absorb the waste products of human existence.  I wanted to believe that solving the carbon fuel problem was for future generations and that the big concern was the limited supply of oil not the rate of adding carbon to the atmosphere. The data is irrefutable--carbon dioxide concentrations have been steadily increasing in our atmosphere as a result of human activity since the earliest measurements began. We know that on the order of 4.1 billion tons of carbon are being added to and staying in our atmosphere each year.  We know that burning fossil fuels and deforestation are the principal contributors to the increasing carbon dioxide concentrations in our atmosphere. Eleven of the last twelve years rank among the warmest years since 1850.  While no one knows for certain the consequences of this continuing unchecked warming, some have argued it could result in catastrophic changes, such as the disruption of the Gulf Steam which keeps the UK out of the ice age or even the possibility of the Greenland ice sheet sliding into the Atlantic Ocean.  Whether or not these devastating changes occur, we are conducting a dangerous experiment with our planet. One we need to stop.

The developed world including the United States, England and Europe contribute disproportionately to the environmental carbon, but the developing world is rapidly catching up.  As the world population increases from 6.5 billion people to 9 billion over the next 45 years and countries like India and China continue to industrialize, some estimates indicate that we will be adding over 20 billion tons of carbon a year to the atmosphere. Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes to the global climate that could be more extreme than those observed to date. This means we can expect more climate change; more ice cap melts, rising sea levels, warmer oceans and therefore greater storms, as well as more droughts and floods, all which compromise food and fresh water production.

It required close to 100,000 years for the human population to reach 1 billion people on Earth in 1804.  In 1960 the world population passed 3 billion and now we are likely to go from 6.5 billion to 9 billion over the next 45 years.  I was born in 1946 when there were only about 2.4 billion of us on the planet, today there are almost three people for each one of us in 1946 and there will soon be four.

Our planet is in crisis, and we need to mobilize all of our intellectual forces to save it. One solution could lie in building a scientifically literate society in order to survive. There are those who like to believe that the future of life on Earth will continue as it has in the past, but unfortunately for humanity, the natural world around us does not care what we believe. But believing that we can do something to change our situation using our knowledge can very much affect the environment in which we live.

For a long time I regarded neuroscience as a fascinating source of information about the workings of the visual system and its dual pathways for sight and action; the fear system in humans and animals, and numerous puzzling pathology cases arising from site-specific lesions.

Yet, despite the interest of these findings, I had little faith that the profusion of fMRI studies of different cortical regions would tell us much about the problems that had pre-occupied philosophers for centuries. After all, some of the greatest minds of history had long pondered the nature of consciousness, the self, the relation between self and others, only to produce a greater realisation of how hard it was to say something illuminating about any of these phenomena. The more one is immersed in neural mechanisms the less one seems to be talking about consciousness, and the more attends to the qualities of conscious experience the less easy it is to connect with the mechanism of the brain. In despair, some philosophers suggested that we must reduce or eliminate the everyday way of speaking about our mental lives to arrive at a science of mind. There appeared to be a growing gulf between how things appeared to us and how reductionist neuroscience told us they were.

However, I have changed my mind about the relevance of neuroscience to philosophers' questions, and vice-versa. Why? Well, firstly because the most interesting findings in cognitive neuroscience are not in the least reductionist. On the contrary, neuroscientists rely on subjects' reports of their experiences in familiar terms to target the states they wish to correlate with increased activity in the cortex. Researchers disrupt specific cortical areas with TMS to discover how subject's experiences or cognitive capacities are altered.

This search for the neural correlates of specific states and abilities has proved far more successful than any reductionist programme; the aim being to explain precisely which neural areas are responsible for sustaining the experiences we typically have as human subjects. And what we are discovering is just how many sub-systems cooperate to maintain a unified and coherent field of conscious experience in us. When any of these systems is damaged what results are bizarre pathologies of mind we find it hard to comprehend. It is here that neuroscientists seek the help of philosophers in analysing the character of normal experience and describing the nature of the altered states. Reciprocally, what philosophers are learning from neuroscience is leading to revisions in cherished philosophical views; mostly for the better. For example, the early stages of sensory processing show considerable cross-modal influence of one sense on another: the nose smells what the eye sees, the tongue tastes what the ear hears, the recognition of voice is enhanced by, and enhances, facial recognition in the fusiform face area; all of which leads us to conclude that the five senses are not nearly as separate as common sense, and most philosophers, have always assumed.

Similar break-throughs in understanding how our sense of self depends on the somatosensory system are leading to revised philosophical thinking about the nature of self. And while philosophers have wondered how individuals come to know about the minds of others, neuroscience assumes the problem to have been partly solved by the discovery of the mirror neuron system which suggests an elementary, almost bodily, level of intersubjective connection between individuals from which the more sophisticated notions of self and other may develop. We don't start, like Descartes, with the self and bridge to our knowledge of other minds. We start instead with primitive social interactions from which the notions of self and other are constructed.

Neuroscientists present us with strange phenomena like patients with lesions in the right parietal region who are convinced that their left arm does not belong to them. Some still feel sensations of pain in their hand but do not believe that it their pain that is felt: something philosophers previously believed to be conceptually impossible.

I think the startling conclusion should be just how precarious the typical experience of the normally functioning mind really is. We should not find it strange to come across people who do not believe their hand belongs to them, or that it acts under someone else's command. Instead, we should think how remarkable it is that this assembly of sub-systems that keeps track of our limbs, our volitions, our position in space, and our recognition of others should cooperate to sustain the sense of self and the feeling of a coherent and unified experience of the world so familiar to us that philosophers have believed it to be the most certain things we know. It isn't the pathology cases of cognitive neuropsychology exceptional: it is the normally functioning minds that we should find the most surprising.

For an empiricist, science brings many surprises. It has continued to change my thinking about many phenomena by challenging my presumptions about them. Among the first of my assumptions to be felled by evidence was that career choice proceeds in adolescence by identifying one's most preferred options; it actually begins early in childhood as a taken-for-granted process of eliminating the least acceptable from further consideration. Another mistaken presumption was that different abilities would be important for performing well in different occupations. The notion that any single ability (e.g., IQ or g) could predict performance to an appreciable degree in all jobs seemed far-fetched the first time I heard it, but that's just what my own attempt to catalog the predictors of job performance would help confirm. My root error had been to assume that different cognitive abilities (verbal, quantitative, etc.) are independent—in today's terms, that there are "multiple intelligences." Empirical evidence says otherwise.     

The most difficult ideas to change are those which seem so obviously true that we can scarcely imagine otherwise until confronted with unambiguous disconfirmation. For example, even behavior geneticists had long presumed that non-genetic influences on intelligence and other human traits grow with age while genetic ones weaken. Evidence reveals the opposite for intelligence and perhaps other human traits as well: heritabilities actually increase with age. My attempt to explain the evolution of high human intelligence has also led me to question another such "obvious truth," namely, that human evolution ceased when man took control of his environment. I now suspect that precisely the opposite occurred. Here is why.

Human innovation itself may explain the rapid increase in human intelligence during the last 500,000 years. Although it has improved the average lot of mankind, innovation creates evolutionarily novel hazards that put the less intelligent members of a group at relatively greater risk of accidental injury and death. Consider the first and perhaps most important human innovation, the controlled use of fire. It is still a major cause of death worldwide, as are falls from man-made structures and injuries from tools, weapons, vehicles, and domesticated animals. Much of humankind has indeed escaped from its environment of evolutionary adaptation (EEA), but only by fabricating new and increasingly complicated physical ecologies. Brighter individuals are better able not only to extract the benefits of successive innovations, but also to avoid the novel threats to life and limb that they create. Unintentional injuries and deaths have such a large chance component and their causes are so varied that we tend to dismiss them as merely "accidental," as if they were uncontrollable. Yet all are to some extent preventable with foresight or effective response, which gives an edge to more intelligence individuals. Evolution requires only tiny such differences in odds of survival in order to ratchet up intelligence over thousands of generations. If human innovation fueled human evolution in the past, then it likely still does today.

Another of my presumptions bit the dust, but in the process exposed a more fundamental, long-brewing challenge to my thinking about scientific explanation. At least in the social sciences, we seek big effects when predicting human behavior, whether we are trying to explain differences in happiness, job performance, depression, health, or income. "Effect size" (percentage of variance explained, standardized mean difference, etc.) has become our yardstick for judging the substantive importance of potential causes. Yet, while strong correlations between individuals' attributes and their fates may signal causal importance, small correlations do not necessarily signal unimportance.

Evolution provides an obvious example. Like the house in a gambling casino, evolution realizes big gains by playing small odds over myriad players and long stretches of time. The small-is-inconsequential presumption is so ingrained and reflexive, however, that even those of us who seek to explain the evolution of human intelligence over the eons have often rejected hypothesized mechanisms (say, superior hunting skills) when they could not explain differential survival or reproductive success within a single generation.

IQ tests provide a useful analogy for understanding the power of small but consistent effects. No single IQ test item measures intelligence well or has much predictive power. Yet, with enough items, one gets an excellent test of general intelligence (g) from only weakly g-loaded items. How? When test items are considered one by one, the role of chance dominates in determining who answers the item correctly. When test takers' responses to many such items are added together, however, the random effects tend to cancel each other out, and g's small contribution to all answers piles up. The result is a test that measures almost nothing but g.

I have come to suspect that some of the most important forces shaping human populations work in this inconspicuous but inexorable manner. When seen operating in individual instances, their impact is so small as to seem inconsequential, yet their consistent impact over events or individuals produces marked effects. To take a specific example, only the calculus of small but consistent tendencies in health behavior over a lifetime seems likely to explain many demographic disparities in morbidity and mortality, not just accidental death.

Developing techniques to identify, trace, and quantify such influences will be a challenge. It currently bedevils behavior geneticists who, having failed to find any genes with substantial influence on intelligence (within the normal range of variation), are now formulating strategies to identify genes that may account for at most only 0.5% of the variance in intelligence.

The central question for students of well-being is the extent to which people adapt to circumstances.  Ten years ago the generally accepted position was that there is considerable hedonic adaptation to life conditions. The effects of circumstances on life satisfaction appeared surprisingly small: the rich were only slightly more satisfied with their lives than the poor, the married were happier than the unmarried but not by much, and neither age nor moderately poor health diminished life satisfaction.  Evidence that people adapt — though not completely — to becoming paraplegic or winning the lottery supported the idea of a "hedonic treadmill": we move but we remain in place.  The famous "Easterlin paradox" seemed to nail it down:  Self-reported life satisfaction has changed very little in prosperous countries over the last fifty years, in spite of large increases in the standard of living.

Hedonic adaptation is a troubling concept, regardless of where you stand on the political spectrum.  If you believe that economic growth is the key to increased well-being, the Easterlin paradox is bad news.  If you are a compassionate liberal, the finding that the sick and the poor are not very miserable takes wind from your sails.   And if you hope to use a measure of well-being to guide social policy you need an index that will pick up permanent effects of good policies on the happiness of the population. 

About ten years ago I had an idea that seemed to solve these difficulties: perhaps people's satisfaction with their life is not the right measure of well-being.  The idea took shape in discussions with my wife Anne Treisman, who was (and remains) convinced that people are happier in California (or at least Northern California) than in most other places.  The evidence showed that Californians are not particularly satisfied with their life, but Anne was unimpressed.  She argued that Californians are accustomed to a pleasant life and come to expect more pleasure than the unfortunate residents of other states.  Because they have a high standard for what life should be, Californians are not more satisfied than others, although they are actually happier.  This idea included a treadmill, but it was not hedonic – it was an aspiration treadmill: happy people have high aspirations.  

The aspiration treadmill offered an appealing solution to the puzzles of adaptation: it suggested that measure of life satisfaction underestimate the well-being benefits of life circumstances such as income, marital status or living in California.  The hope was that measures of experienced happiness would be more sensitive.  I eventually assembled an interdisciplinary team to develop a measure of experienced happiness (Kahneman, Krueger, Schkade, Stone and Schwarz, 2004) and we set out to demonstrate the aspiration treadmill.   Over several years we asked substantial samples of women to reconstruct a day of their life in detail.  They indicated the feelings they had experienced during each episode, and we computed a measure of experienced happiness: the average quality of affective experience during the day.  Our hypothesis was that differences in life circumstances would have more impact on this measure than on life satisfaction.  We were so convinced that when we got our first batch of data, comparing teachers in top-rated schools to teachers in inferior schools, we actually misread the results as confirming our hypothesis.  In fact, they showed the opposite: the groups of teachers differed more in their work satisfaction than in their affective experience at work. This was the first of many such findings: income, marital status and education all influence experienced happiness less than satisfaction, and we could show that the difference is not a statistical artifact.  Measuring experienced happiness turned out to be interesting and useful, but not in the way we had expected.  We had simply been wrong.

Experienced happiness, we learned, depends mainly on personality and on the hedonic value of the activities to which people allocate their time.  Life circumstances influence the allocation of time, and the hedonic outcome is often mixed: high-income women have more enjoyable activities than the poor, but they also spend more time engaged in work that they do not enjoy; married women spend less time alone, but more time doing tedious chores.  Conditions that make people satisfied with their life do not necessarily make them happy.  

Social scientists rarely change their minds, although they often adjust their position to accommodate inconvenient facts. But it is rare for a hypothesis to be so thoroughly falsified.  Merely adjusting my position would not do; although I still find the idea of an aspiration treadmill attractive, I had to give it up.

To compound the irony, recent findings from the Gallup World Poll raise doubts about the puzzle itself.  The most dramatic result is that when the entire range of human living standards is considered, the effects of income on a measure of life satisfaction (the "ladder of life") are not small at all.  We had thought income effects are small because we were looking within countries.  The GDP differences between countries are enormous, and highly predictive of differences in life satisfaction.  In a sample of over 130,000 people from 126 countries, the correlation between the life satisfaction of individuals and the GDP of the country in which they live was over .40 – an exceptionally high value in social science.  Humans everywhere, from Norway to Sierra Leone, apparently evaluate their life by a common standard of material prosperity, which changes as GDP increases. The implied conclusion, that citizens of different countries do not adapt to their level of prosperity, flies against everything we thought we knew ten years ago.  We have been wrong and now we know it.  I suppose this means that there is a science of well-being, even if we are not doing it very well.

I used to think that the most fascinating thing about physics was theory — and that the best was still to come. But as physics has grown vanishingly abstract I've been drawn in the opposite direction, to the great experiments of the past.

First I determined to show myself that electrons really exist. Firing up a beautiful old apparatus I found on eBay — a bulbous vacuum tube big as a melon mounted between two coils — I replayed J. J. Thomson's famous experiment of 1897 in which he measured the charge-to-mass ratio of an electron beam. It was thrilling to see the bluish-green cathode ray dive into a circle as I energized the electromagnets. Even better, when I measured the curve and plugged all the numbers into Thomson's equation, my answer was off by only a factor of two. Pretty good for a journalist. I had less success with the stubborn Millikan oil-drop experiment. Mastering it, I concluded, would be like learning to play the violin.

Electricity in the raw is as mysterious as superstrings. I turn down the lights and make my Geissler tubes glow with the touch of a high-voltage wand energized by a brass-and-mahogany Ruhmkorff coil. I coax the ectoplasmic rays in my de la Rive tube to rotate around a magnetized pole.

Maybe in a year or two, the Large Hadron Collider will make this century's physics interesting again. Meanwhile, as soon as I find a nice spinthariscope, I'm ready to go nuclear.

I was a science geek with a religious upbringing, an Episcopalian upbringing, to be precise, which is pretty weak tea as far as pious fervor goes. Raised in this tradition I learned, without ever being explicitly taught, that religion and science were compatible. My people had no truck with Young Earth Creationism or anti-evolutionary cant, thank you very much, and if some people's views clashed with scientific discovery, well, that was their fault for being so fundamentalist.

Since we couldn't rely on the literal truth of the Bible, we needed a fallback position to guide our views on religion and science. That position was what I'll call the Doctrine of Joint Belief: "Noted Scientist X has accepted Jesus as Lord and Savior. Therefore, religion and science are compatible." (Substitute deity to taste.) You can still see this argument today, where the beliefs of Francis Collins or Freeman Dyson, both accomplished scientists, are held up as evidence of such compatibility.

Belief in compatibility is different from belief in God. Even after I stopped believing, I thought religious dogma, though incorrect, was not directly incompatible with science (a view sketched out by Stephen Gould as "non-overlapping magisteria".)  I've now changed my mind, for the obvious reason: I was wrong. The idea that religious scientists prove that religion and science are compatible is ridiculous, and I'm embarrassed that I ever believed it. Having believed for so long, however, I understand its attraction, and its fatal weaknesses.

The Doctrine of Joint Belief isn't evidence of harmony between two systems of thought. It simply offers permission to ignore the clash between them. Skeptics aren't convinced by the doctrine, unsurprisingly, because it offers no testable proposition. What issurprising is that its supposed adherents don't believe it either. If joint beliefs were compatible beliefs, there could be no such thing as heresy. Christianity would be compatible not just with science, but with astrology (roughly as many Americans believe in astrology as evolution), with racism (because of the number of churches who use the "Curse of Ham" to justify racial segregation), and on through the list of every pair of beliefs held by practicing Christians.

To get around this, one could declare that, for some arbitrary reason, the co-existence of beliefs is relevant only to questions of religion and science, but not to astrology or anything else. Such a stricture doesn't strengthen the argument, however, because an appeal to the particular religious beliefs of scientists means having to explain why the majority of them are atheists. (See the 1998 Larson and Witham study for the numbers.) Picking out the minority who aren't atheists and holding only them up as exemplars, is simply special pleading (not to mention lousy statistics.)

The works that changed my mind about compatibility were Pascal Boyer's Religion Explained, and Scott Atran's In Gods We Trust, which lay out the ways religious belief is a special kind of thought, incompatible with the kind of skepticism that makes science work. In Boyer and Atran's views, religious thought doesn't simply happen to be false -- being false is the point, the thing that makes belief both memorable and effective. Psychologically, we overcommit to the ascription of agency, even when dealing with random events (confirmation can be had in any casino.) Belief in God rides in on that mental eagerness, in the same way optical illusions ride in on our tendency to overinterpret ambiguous visual cues. Sociologically, the adherence to what Atran diplomatically calls 'counter-factual beliefs' serves both to create and advertise in-group commitment among adherents. Anybody can believe in things that are true, but it takes a lot of coordinated effort to get people to believe in virgin birth or resurrection of the dead.

We are early in one of the periodic paroxysms of conflict between faith and evidence. I suspect this conflict will restructure society, as after Galileo, rather than leading to a quick truce, as after Scopes, not least because the global tribe of atheists now have a medium in which they can discover one another and refine and communicate their message.

One of the key battles is to insist on the incompatibility of beliefs based on evidence and beliefs that ignore evidence. Saying that the mental lives of a Francis Collins or a Freeman Dyson prove that religion and science are compatible is like saying that the sex lives of Bill Clinton or Ted Haggard prove that marriage and adultery are compatible. The people we need to watch out for in this part of the debate aren't the fundamentalists, they're the moderates, the ones who think that if religious belief is made metaphorical enough,  incompatibility with science can be waved away. It can't be, and we need to say so, especially to the people like me, before I changed my mind.

As a child, I was told that hot water freezes faster than cold water. This was easy to refute in principle, so I did not believe it.

Many years later I learned that Aristotle had described the effect in his Meteorologica,

"The fact that the water has previously been warmed contributes to its freezing quickly: for so it cools sooner. Hence many people, when they want to cool hot water quickly, begin by putting it in the sun. So the inhabitants of Pontus when they encamp on the ice to fish (they cut a hole in the ice and then fish) pour warm water round their reeds that it may freeze the quicker, for they use the ice like lead to fix the reeds. " (E. W. Webster translation)

I was impressed as always by Aristotle's clarity, confidence and specificity. Of course, I do not expect you to be convinced that it is true simply because Aristotle said so, especially since his explanation is that "warm and cold react upon one another by recoil." (Aristotle, like us, was very good making up explanations to justify his beliefs). Instead, I hope that you will have the pleasure of being convinced, as I was, by trying the experiment yourself.

Rather than choose a personal example of a change in mind, I reflect on instances in which my field, medicine, has apparently changed "its" mind based on changes in evidence. In my experience major reversals in belief (as opposed to simply progressions, or changes in course) typically arise when there are serious flaws in evaluation of evidence or inference leading to the old view, the new view, or both.

To be committed to a view based on facts, and later find the view wrong, either the facts had to be wrong or the interpretation of them had to extend beyond what the facts actually implied. The "facts" can be wrong in a range of settings: academic fraud, selective documentation of research methods, and selective publication of favorable results — among many. But in my experience more often it is the interpretation of the facts that is amiss.

Hormone replacement therapy ("HRT") is a case in point. You may recall HRT was widely hailed as slashing heart disease and dementia risk in women. After all, in observational studies — with large samples --women who took HRT had lower rates of heart disease and Alzheimer's than women who did not.

I was not among those advising patients that HRT had the benefits alleged. Women who took HRT (indeed any preventive medication) differed from those who did not. These differences include characteristics that might be expected to produce the appearance of a protective association, through "confounding." For instance, people who get preventive health measures have better education and higher income — which predict less dementia and better health, irrespective of any actual effect of the treatment. (Efforts to adjust for such factors can never be trusted to capture differences sufficiently.) These disparities made it impossible to infer from such "observational" data alone whether the "true" causal relationship of hormone replacement to brain function and heart events was favorable, neutral, or adverse.

When controlled trials were finally conducted — with random allocation to HRT or placebo providing that the compared groups were actually otherwise similar — HRT was found rather to increase rates of heart-related events and dementia. But the lessons from that experience have not been well learned, and new, similarly flawed "findings" continue to be published — without suitable caveats.

It is tempting to provide a raft of other examples in which a range of errors in reasoning from evidence were present, recognition of which should have curbed enthusiasm for a conclusion, but I will spare the reader.

Stunningly, there is little mandated training in evaluation of evidence and inference in medical school — nor indeed in graduate school in the sciences. (Nor are the medical practice guidelines on which your care is grounded generated by people chosen for this expertise.)

Even available elective coursework is piecemeal. Thus, statistics and probability courses each cover some domains of relevance such as study "power," or distinguishing posterior from a priori probabilities: thus it may be that commonly if a wife who was beaten is murdered, the spouse is the culprit (a posteriori), even if it is uncommon for wife beaters to murder their spouse (a priori). Epidemiology-methods courses address confounding and many species of bias.Yet instruction in logical fallacies, for instance, was absent completely from the available course armamentarium. Each of these domains, and others, are critical to sound reasoning from evidence.

Preventive treatments should mandate a high standard of evidence. But throughout the "real world" decisions are required despite incomplete evidence. At a level of information that should not propel a strong evidence-driven "belief," a decision may nonetheless be called for: How to allocate limited resources; whom to vote for; and whether to launch a program, incentive, or law. Even in these domains, where the luxury of tightly controlled convergent evidence is unattainable — or perhaps especially in these domains — understanding which evidence has what implications remains key, and may propel better decisions, and restrain unintended consequences.

The haphazard approach to training in reasoning from evidence in our society is, in its way, astounding — and merits a call to action. Better reasoning from evidence is substantially teachable but seldom directly taught, much less required. It should be central to curriculum requirements, at both graduate (advanced) and undergraduate (basic) levels — if not sooner.

After all, sound reasoning from evidence is (or ought to be) fundamental for persons in each arena in which decisions should be rendered, or inferences drawn, on evidence: not just doctors and scientists, but journalists, policy makers — and indeed citizens, whose determinations affect not solely their own lives but others', each time they parent, serve on juries, and vote.

I used to believe that a paramount purpose of a liberal education was threefold:

1) Stretch your mind, reach beyond your preconceptions; learn to think of things in ways you have never thought before.

2) Acquire tools with which to critically examine and evaluate new ideas, including your own cherished ones.

3) Settle eventually on a framework or set of frameworks that organize what you know and believe and that guide your life as an individual and a leader.

I still believe #1 and #2. I have changed my mind about #3. I now believe in a new version of #3, which replaces the above with the following:

a) Learn new frameworks, and be guided by them.

b) But never get so comfortable as to believe that your frameworks are the final word, recognizing the strong psychological tendencies that favor sticking to your worldview. Learn to keep stretching your mind, keep stepping outside your comfort zone, keep venturing beyond the familiar, keep trying to put yourself in the shoes of others whose frameworks or cultures are alien to you, and have an open mind to different ways of parsing the world. Before you critique a new idea, or another culture, master it to the point at which its proponents or members recognize that you get it.

Settling into a framework is easy. The brain is built to perceive the world through structured lenses — cognitive scaffolds on which we hang our knowledge and belief systems.

Stretching your mind is hard. Once we've settled on a worldview that suits us, we tend to hold on. New information is bent to fit, information that doesn't fit is discounted, and new views are resisted.

By 'framework' I mean any one of a range of conceptual or belief systems — either explicitly articulated or implicitly followed. These include narratives, paradigms, theories, models, schemas, frames, scripts, stereotypes, and categories; they include philosophies of life, ideologies, moral systems, ethical codes, worldviews, and political, religious or cultural affiliations. These are all systems that organize human cognition and behavior by parsing, integrating, simplifying or packaging knowledge or belief. They tend to be built on loose configurations of seemingly core features, patterns, beliefs, commitments, preferences or attitudes that have a foundational and unifying quality in one's mind or in the collective behavior of a community. When they involve the perception of people (including oneself), they foster a sense of affiliation that may trump essential features or beliefs.

What changed my mind was the overwhelming evidence of biases in favor of perpetuating prior worldviews. The brain maps information onto a small set of organizing structures, which serve as cognitive lenses, skewing how we process or seek new information. These structures drive a range of phenomena, including the perception of coherent patterns (sometimes where none exists), the perception of causality (sometimes where none exists), and the perception of people in stereotyped ways.

Another family of perceptual biases stems from our being social animals (even scientists!), susceptible to the dynamics of in-group versus out-group affiliation. A well known bias of group membership is the over-attribution effect, according to which we tend to explain the behavior of people from other groups in dispositional terms ("that's just the way they are"), but our own behavior in much more complex ways, including a greater consideration of the circumstances. Group attributions are also asymmetrical with respect to good versus bad behavior. For groups that you like, including your own, positive behaviors reflect inherent traits ("we're basically good people") and negative behaviors are either blamed on circumstances ("I was under a lot of pressure") or discounted ("mistakes were made"). In contrast, for groups that you dislike, negative behaviors reflect inherent traits ("they can't be trusted") and positive behaviors reflect exceptions ("he's different from the rest"). Related to attribution biases is the tendency (perhaps based on having more experience with your own group) to believe that individuals within another group are similar to each other ("they're all alike"), whereas your own group contains a spectrum of different individuals (including "a few bad apples"). When two groups accept bedrock commitments that are fundamentally opposed, the result is conflict — or war.

Fortunately, the brain has other systems that allow us to counteract these tendencies to some extent. This requires conscious effort, the application of critical reasoning tools, and practice. The plasticity of the brain permits change - within limits.

To assess genuine understanding of an idea one is inclined to resist, I propose a version of Turing's Test tailored for this purpose: You understand something you are inclined to resist only if you can fool its proponents into thinking you get it. Few critics can pass this test. I would also propose a cross-cultural Turing Test for would-be cultural critics (a Golden Rule of cross-group understanding): before critiquing a culture or aspect thereof, you should be able to navigate seamlessly within that culture as judged by members of that group.

By rejecting #3, you give up certainty. Certainty feels good and is a powerful force in leadership. The challenge, as Bertrand Russell puts it in The History of Western Philosophy, is "To teach how to live without certainty, and yet without being paralyzed by hesitation".

I used to take the view that public consultations about science policy were pointless. While the idea of asking ordinary people's opinions about controversial research sounds quite reasonable, it is astonishingly difficult to do well.

When governments canvass about issues such as biotechnology or embryo research, what usually happens is that the whole exercise gets captured by special interests.

A vocal minority with strong opinions that are already widely known and impervious to argument — think Greenpeace and the embryo-rights lobby — get their responses in early and often. The much larger proportion of people who consider themselves neutral, open to persuasion, uninformed or uninterested rarely bother to take part. Public opinion is then deemed to have spoken, without reflecting true public opinion at all. Wouldn't it be better, I thought, to let scientists get on with their research, subject to occasional oversight by specialist panels with appropriate ethical expertise?

Well, to a point. Public consultations can indeed be worse than useless, particularly when the British Government has done the consulting: its exercises on GM crops and embryo research laws were particularly ill-judged. As Sir David King said recently, they have taught us what not to do.

Their failure, though, has stimulated some interesting thinking that has convinced me that it is possible to engage ordinary people in quite complex scientific issues, without letting the usual suspects shout everybody else down.

The Human Fertilisation and Embryology Authority's recent work on cytoplasmic hybrid embryos is a case in point. The traditional part of the exercise had familiar results: pro-lifers and anti-genetic engineering groups mobilised, so 494 of the 810 written submissions were hostile. Careful questioning, however, established that almost all these came from people who oppose all embryo research in all circumstances.

A more scientific poll found 61 per cent backing for interspecies embryos, if these were to be used for medical research. Detailed deliberative workshops revealed that once the rationale for the experiments was properly explained, large majorities overcame "instinctive repulsion" and supported the work.

If consultations are properly run in this way, there is a lot to be said for them. They can actually build public understanding of potentially controversial research, and shoot the fox of science's shrillest critics.

In many ways, they are rather more helpful than seeking advice from bioethicists, whose importance to ethical research I've increasingly come to doubt. It's not that philosophy of science is not a worthwhile academic discipline — it can be stimulating and thought-provoking. The problem is that a bioethicist can almost always be found to support any position.

Leon Kass and John Harris are both eminent bioethicists, yet the counsel you would expect them to give on embryo research laws is going to be rather different. Politicians — or scientists — can and do deliberately appoint ethicists according to their pre-existing world views, then trumpet their advice as somehow independent and authoritative, as if their subject were physics.

If specialist bioethics has a role to play in regulation of science, it is in framing the questions that researchers and the public at large should consider. It can't just be a fig leaf for decisions people were always going to make anyway.