Professor of Evolutionary Biology, Reading University, UK, Fellow of the Royal Society, author Wired for Culture: Origin of the Human Social Mind

The Internet isn't changing the way I or anybody else thinks. We know this because we can still visit some people on Earth who don't have the Internet and they think the same way that we do. My general purpose thinking circuits are hard wired into my brain from genetic instructions honed over millions of years of natural selection. True, the brain is plastic, it responds to the way it is brought up by its user, or to the language it has been taught to speak, but its fundamental structure is not changed this way, except perhaps in extremis, maybe eight hours per day of computer games.

But the Internet does takes advantage of our appetites, and this changes our thoughts, if not the way we think. Our brains have appetites for thinking, learning, feeling, hearing and seeing. They like to be used. It is why we do crossword puzzles and brain-teasers, read books and visit art galleries, watch films, and play or listen to music. Our brain appetites act as spurs to action, in much the same way that our emotions do; or much the same way that our other appetites — for food and sex — do. Those of us throughout history who have acted on our world — even if just to wonder why fires start, why the wind blows out of the southwest, or what would happen if we combined heat with clay, will have been more successful than those of us who sat around waiting for things to happen.

So, the Internet is brain candy to me and, I suspect, to most of us — it slakes our appetite to keep our brain occupied. That moment when a search engine pops up its 1,278,000 search results to my query is a moment of pure injection of glucose into my brain. It loves it. It is why so many of us keep going back for more. Some think that this is why the Internet is going to make us lazy, less-literate, and less-numerate, that we will forget what lovely things books are, and so on. But even as brain candy I think the Internet's influence on these sorts of capabilities and pleasures is probably not as serious as the curmudgeons and troglodytes would have you believe. They will be the same people who grumbled about the telegraph, trains, the motorcar, the wireless, and television.

There are far more interesting ways that the Internet changes our thoughts, and especially the conclusions we draw, and it does this also by acting on our appetites. I speak of contagion, false beliefs, neuroses — especially medical and psychological — conspiracy theories, and narcissism. The technical point is this: the Internet tricks us into doing bad mathematics; it gets us to do a mathematical integration inside our brains that we don't know how to do. What? In mathematics, integration is a way of summing an infinite number of things. It is used to calculate quantities like volumes, areas, rates, and averages. Our brains evolved to judge risks, to assess likelihood or probabilities, to defend our minds against undue worry, and to infer what others are thinking, by sampling and summing or averaging across small groups of people, most probably the people in my tribe. They do this automatically, and normally without us even knowing about it.

In the past my assessment of the risk of being blown up by a terrorist, or of getting swine flu, or of my child being snatched by a pedophile on the way to school, was calculated from the steady input of information I would have received mainly from my small local group, because these were the people I spoke to or heard from and these were the people whose actions affected me.

What the Internet does, and what mass communication does more generally is to sample those inputs from the 6.8 billion people on Earth. But my brain is still considering that the inputs arose from my local community, because that is the case its assessment circuits were built for. That is what I mean by bad mathematics. My brain assumes a small denominator (that is the bottom number in a fraction) with the result that the answer to the question of how likely something is to happen is too big.

So, when I hear every day of children being snatched my brain gives me the wrong answer to the question of risk: it has divided a big number (the children snatched all over the world) by a small number (the tribe). Call this the 'Madeleine McCann' effect. We all heard months of coverage of this sad case of kidnapping — still unresolved — and although trivial compared to what the McCann's suffered, it has caused undue worry in the rest of us.

The effects of the bad mathematics don't stop with judging risks. Doing the integration wrong, means that contagion can leap across the Internet. Contagion is a form of risk assessment with an acutely worrying conclusion. Once it starts on the Internet, everyone's bad mathematics make it explode. So, do conspiracy theories: if it seems everyone is talking about something, it must be true! But this is just the wrong denominator again. Neuroses and false beliefs are buttressed: we all worry about our health and in the past would look around us and find that no one else is worrying or ill. But consult the Internet and 1,278,000 people (at least!) are worrying, and they've even developed Websites to talk about their worry. The 2009 swine flu pandemic has been a damp squib but you wouldn't have known that from the frenzy.

The bad mathematics can also give us a sense that we have something useful to say. We'd all like to be taken seriously and evolution has probably equipped us to think we are more effective than we really are, it seeds us with just that little bit of narcissism. A false belief perhaps but better for evolution to err on the side of getting us to believe in ourselves than not to. So, we go up on the Internet and make Websites, create Facebook pages, contribute to YouTube and write Web logs and, surprise, it appears that everyone is looking at or reading them, because look at how many people are leaving comments! Another case of the wrong denominator.

The maddening side of all this is that neither I nor most others can convince ourselves to ignore these worries, neuroses, narcissistic beliefs and poor assessments of risk — to ignore our wrong thoughts — precisely because the Internet has not changed the way we think.