I find these developments to be exhilarating; they are a fulfillment of the ancient imperative to know thyself. They also have important practical implications. Alzheimer's Disease, to cite just one example, will be one of the leading causes of human misery in the industrial world over the next several decades, as we live longer and stop dying of other things. Successful treatment of Alzheimer's will not come from prayer or wishful thinking or reasoning about soul one; it will come from treating memory and personality as biochemical phenomena.

Nonetheless, as I mentioned at the outset, not everyone shares this excitement. Sometimes the reaction of people who learn about these new sciences is uneasy ambivalence. The American author Tom Wolfe wrote an article called "Sorry, But Your Soul Just Died," a mixture of admiration and apprehension over the frontiers of cognitive neuroscience and evolutionary psychology. A reviewer of my book How the Mind Works, alluding to the rock and roll band, said that I was describing people as Meat Puppets, and several reviewers, to my puzzlement, asked whether, if I were right, life would be worth living. I am puzzled by these reactions, which are never backed up by argument, only by indignation and high dudgeon. But I'll do my best to recover the values and reasoning that lead to them, and to show why I think they are misguided.

One reason I find the reaction strange is that I can't imagine how anything coming out of the laboratory, computer, or theoretician's notebook could possibly subtract from what is the meaning of life, or Richard's sense of Soul two. Why keep on living if our minds are the physiological activity of the brain? Well, for starters there's natural beauty, and works of great art, and ethical ideals, and love, and bringing up children, and enjoying friends, and discovering how the world works -- I could go on. Why should the worth of any of those activities depend on the existence of a ghost in the machine?

Clearly there can be reasons that some people feel threatened by the idea that the mind is the activity of the brain, and here are my guesses about what they are. One is that since natural selection is not a process that is guaranteed to produce niceness, many typical human motives will not necessarily lead to ethically desirable outcomes. Much of the research in evolutionary psychology has shown that many ignoble motives have some basis in natural selection. An example is the desire, most obvious in men, to defend one's honor and reputation, by violence if necessary. Another is the characteristically male motive to seek a variety of sexual partners. It's easy to work out why those motives evolved, and there is by now an enormous body of evidence that they are widespread among humans. But people reject the explanation because of what they think is the subtext. If these motives are part of our nature, if they come from the natural world, well, everyone knows that natural things are good -- natural childbirth, natural yogurt, and so on -- so that would imply that promiscuity and violence aren't so bad after all. And it implies that since they are "in the genes," they are unchangeable, and attempts to improve the human condition are futile.

I think both parts are wrong -- the first part is so obviously wrong that it has been given a name, the naturalist fallacy, the idea that what we find in nature is good. What we find in nature is not necessarily good; as Richard has put it, the universe is not good or bad, it's indifferent. Certainly violence and philandering and all of the other sins are immoral whether their cause is the genes, or the wiring of the brain, or social conditioning, or anything else. It behooves us to find the causes, but the causes don't change the moral coloring of those acts.

Also, the human mind, I argue, is a complex system of many interacting parts. Even if one motive impels people to do immoral acts, other parts of the mind that can subvert its designs. We can think of the long-term consequences, and we can imagine what society would be like if everyone acted on a particular motive. The part of the mind that has those thoughts can disengage the part of the mind that has less noble motives.