Unlike most philosophers, Daniel Dennett believes we can build a human being and that all the mind's work is just the sum of mechanical systems that make up the brain. Harriet Swain reports

As a senior at a top American prep school in New Hampshire, philosopher Daniel Dennett performed the part of a Bible-seller in Inherit the Wind, a play about the trial of John T. Scopes. Scopes was a schoolteacher thrown into jail for daring to teach evolutionary theory in an era when most Americans believed in the biblical account of creation -God making the world in six days, including Adam. "That is when I became interested in evolution," Dennett says. "When I was learning about the background to the Scopes trial and hawking my Bibles on the stage."

Since then, he has become one of the most dedicated fans of the theory of evolution by natural selection. "To put it bluntly but fairly," he writes in his book, Darwin's Dangerous Idea: Evolution and the Meanings of Life, "anyone today who doubts that the variety of life on this planet was produced by a process of evolution is I inexcusably ignorant, in a world where three out of four people have learned to read and write."

Dennett, 57, settles his imposing frame behind his desk at Tufts University, a private university outside Boston, where he has striven to be blunt but fair since 1971, when he first joined the philosophy department there. On his office wall are four reproductions of Marilyn Monroe - identical, except that one is doodled with a moustache. The faces may seem frivolous, but in fact they make a serious point about how easily we can be deceived. Because our brains can only process a limited number of images a second, we assume, in this case wrongly, that every picture in the series is exactly the same.

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A pink plastic brain sits on the desk and behind him is a transparent model of a head, filled with wires. This last represents Dennett's controversial belief that what we think, remember and feel, all the mind's work, is no more than the sum of mechanical systems making up the brain.

Dennett's international reputation is partly founded on his sympathy for scientific approaches towards problems originally defined by philosophers, problems such as "What is human consciousness?" He argues that those studying the mind need make no distinction between what he calls "Easy Problems", those concerning the mechanics of nerve and brain cells, and "Hard Problems", which are to do with what philosophers call qualia - the way things look or smell or feel to us. "Once all the Easy Problems are solved, consciousness is explained," he says.

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The way the easy problems are solved is by applying the theory of evolution - the process by which genes copy themselves to produce the genes of the next generation, making errors that lead to new characteristics and surviving, through natural selection, only if the errors are beneficial. It is, he says, a "universal acid" that dissolves all other explanations, such as religion, ethics, economics, biology. No God or great designer is needed, simply a blind, mechanical algorithm. Indeed, Dennett is scathing about what he calls "skyhook" explanations, such as religion, that rely on imaginary supports to describe why things are the way they are. Instead, he favours concrete, mechanical explanations, which he calls "cranes".

"The traditional idea of a sacrosanct pearl of genius that is outside the realm of the mechanistic and is the source of creativity is just a hopeless idea, a fantasy," he says. "I know some people find this notion offensive, but that is too bad for them. My job is to cajole them out of their squeamishness."

His is not a bleak view, he insists. He has no time for those who dismiss evolution as denying the existence of human creativity. "Look how creative it is!" he cries. "It has created every life form on the planet. If it can make a skylark, then it can make Keats's poem Ode to a Nightingale. The skylark is at least as wonderful as Ode to a Nightingale, and the processes that have produced the skylark are, in the end, mechanical, algorithmic."

Dennett's research goes further, developing the idea that even free will is the product of evolution. It has evolved, he says, just as language has evolved, and distinguishes human beings from animals in much the same way. He says that many people are terrified of accepting that free will is nothing more than the outcome of a mechanical process. It is this fear, in turn, that fuels their opposition to the idea that the brain is a computer and human consciousness a process that will one day be described down to the last detail by scientists.

"I want to say to them, 'You are absolutely right'," he says. "Human freedom is the most important thing there is. But the way to protect it, to understand what it is and preserve it is not to try to dig a moat around it and protect it from science, but to see how it evolves and see how it is perceived in a computational way."

Dennett is not in the habit of telling his fellow academics they are right. He is a stalwart of academic argument, taking swipes at such revered thinkers as Stephen J. Gould, Noam Chomsky, John Searle and Roger Penrose. He tells a story about the biochemist Gerald Edelman once refusing to shake his hand and walking out of the room when Dennett tried to introduce his wife to him at a meeting in Switzerland.

Darwin's Dangerous Idea was a sustained attack on people such as Gould, Chomsky and Edelman. Dennett says they misunderstood Darwinian evolution. In Consciousness Explained, published in 1991, he had already demolished the work of anyone who suggested that human consciousness would never be fully explained.

What he most hates is an academic bully - "a silverback in his field who wilfully caricatures the views of the other side".

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"I get angry when people abuse their visibility, influence and authority," he says. "I try not to do it myself. I have tried to make it a rule that I don't slam people unless they are really big and they really deserve it."

He is, however, quick to credit those academics who have helped and influenced his career - Gilbert Ryle, his doctoral supervisor at Oxford University in the 1960s, for example, or Richard Dawkins, the same university's professor of the public understanding of science. He has relied on the goodwill of scientists to tell him about their field because his background was entirely in the arts. His father, who was killed in an aeroplane crash when Dennett was five, was a professor of Islamic history. His mother was a librarian and textbook editor.

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When Dennett and his sisters were sent off to Sunday school in New Hampshire, he memorised the order of books in the Bible. One sister grew up to be a director of religious education. "I understand the emotional treasures of religion as it were from the inside, and so I am more sympathetic to religion than some," he says.

This is curious in the light of past statements such as "safety demands that religions be put in cages". He has often cited religion as one of the most dangerous "skyhooks".

But he says: "At its best, religion can structure and fill human lives with meaning that enriches those lives and makes the world a better place. One tampers with that at the peril of everybody."

The problem for an academic is that the comfort Dennett acknowledges religion offers involves deliberate misrepresentation. But in day-to-day life white lies are sometimes necessary, he says. "I think there is an understandable and somewhat defensible default position among academics and scientists that the truth is the highest good and, as long as it is true, that is defensible. I do not believe that. I think there are clear cases where we have to think much more deeply about the effect of truth on the world."

This is because truths are so often misused and misunderstood. Dennett suggests: "Academics should think about holding themselves responsible for the likely misinterpretations of what they say."

Dennett is, after all, a proponent of Dawkins's concept of memes - ideas, fashions, behaviours and skills passed on from person to person by imitation, competing against one another for survival and being distorted in the process, subject to the evolutionary process in the same way as genes.

He is well aware of the dangers inherent in this. "When you let fly a meme, and watch it get mutated by the public, you see how something you have released into the cultural soup is taking on a life of its own and perhaps developing in ways you don't like."

It was at Oxford, working for a DPhil, that Dennett developed a fascination with the mind. There he began to devour medical textbooks and seek out people who could tell him about neuroscience. "I decided that if I was going to do philosophy of mind, I had to know about the relevant science," he says.

The upshot of his Oxford reading, followed by a period teaching at the University of California, Irvine, was a series of books with enviable sales figures - Content and Consciousness, Brainstorms, The Mind's I, written with Douglas Hofstadter, and Elbow Room. By this time he was back home, teaching philosophy at Tufts, where he has remained. For the past six years, he has also been an adviser to a team at the Massachusetts Institute of Technology creating Cog, a robot baby, able to see, feel and learn.

He works "in my own little personal imitation of natural selection. I'm a pack rat. I scrounge around. I find lots of things that I think interesting I I pick up techniques and then, of course, visions, methods, and then I chew on them and fiddle with them and let them spin around in my head and put them together in weird combinations."

Dennett believes he hit on some really good ideas about evolution early on and has revelled in watching them develop over the years. While some theories need constant patching up or are ultimately doomed, this is not always the case. "When you turn a crank, there are new insights."

This is why he has never acted on his vague fantasy of retiring to the family farm in Maine, where he spends his summers making cider and cutting up firewood. While he loves dealing with concrete issues in contrast to the "preciousness" of academic life, he would miss the stimulation of his students.

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So he keeps his back-to-nature instincts for the summer and relaxes by wittling away at sculptures and carvings. Recently, cruising with friends along the coast of Greenland, he encountered tupelaks - fetish figures, part animal, part person - which Greenlanders carve out of reindeer antlers and often use as tools for cursing their foes. Fascinated, Dennett secured a supply of antlers and started working away at his own variations.