The cognitive scientist Zenon Pylyshyn suggests rocks are smarter than cats because rocks at least have the sense to go away when you kick them. Steven Pinker's mischievous sense of humour throws up this quote, and many other provocative ones in this detailed account of reverse-engineering the human mind.
Reverse-engineering, explains Pinker, is what the boffins at Sony do when a new product is announced by Panasonic, or vice versa. They buy one, take it back to the lab, pull it apart and try to figure out what all the parts are for and how they combine to make the device work.
It was only by attempting to build artificial intelligence that people discovered much of the human mind's incredible complexity.
Pinker reverse-engineers the human mind by asserting that it is a collection of computation devices designed by natural selection to solve the kinds of problems our ancestors faced in their foraging life on the African savannah. In particular, understanding and out-manoeuvring objects,animals, plants and other people.
Now most commonly referred to as evolutionary psychology, this approach had a previous incarnation as sociobiology but developed such a bad press among left-wing social scientists that it was renamed by followers afraid of being "outed".
Aware of such prejudice against this form of analysis, Pinker, professor of psychology and director of the Centre for Cognitive Neuroscience at the Massachusetts Institute of Technology, takes care to defend his claims with great charm and rigour. For example, he refutes the famous anti-natural selection arguments: how does a process dependent on mere chance produce such an intricate organ as the eye? Stages along the way, goes the objection, would have necessitated "half-an-eye" or, to take another example, "half-a-wing " - both of which seem to confer little, if any, survival advantage.
But Pinker points to computer modelling experiments. These have demonstrated that random mutations and natural selection lead to a simple sandwich made up of a layer of pigmented cells on the bottom, a layer of light-sensitive cells above it, and a layer of translucent cells forming a protective cover, to evolve eventually into an eye, including a retina and cornea. The computer predicts this occurs in 400,000 generations - a mere geological eyeblink.
A wide range of human behaviour is convincingly explained by Pinker's argument that the human mind evolved to solve problems presented to us by the particular ecological niche we adapted to - the African savannah. When American children are shown slides of landscapes and asked how much they would like to visit or live in them, the children prefer savannahs, even though they have never been to one - but they don't like rainforests or deserts. Pinker believes they are revealing our species' habitat preference, sown into our genes.
However it is clear that this evolutionary approach is more powerful and complete when it comes to some of the mind's functions, but with others leaves gaping holes you could drive a horde of sociologists through. For example, the sections of the book detailing how sight and recognition are handled by the mind, and speculating about how these functions evolved, occupy more than 100 pages of elegantly marshalled evidence - but then that was probably always territory the social scientists would have been happy to give up. They will however fight a more tenacious rearguard action over emotions and motivations which dominate everyday social life, and which defy simple biological reductionism. Yet Pinker relentlessly extends his evolutionary psychology analysis to storm even these barricades, producing sociobiological accounts of why the mind manufactures and appreciates humour, art, music and religion.
He struggles more when aiming at these targets. He gives his evolutionary theory only three pages to explain happiness, while grief, a universal human emotion, gets less than one page - including the statement: "No one knows what, if anything, grief is for". This is bad timing for an academic publishing within a few months of the Princess Diana bereavement phenomenon.
Pinker is aware of these problems. He himself asks: where is the Darwinian imperative to survive and reproduce in an age when people watch pornography when they should be seeking a mate, forgo food to buy heroin, sell their blood to buy movie tickets (in India), postpone childbearing to climb the corporate ladder and eat themselves into an early grave?
For someone who still teaches the introductory psychology course at MIT, his neglect of social and clinical psychological answers to these questions is curious, but perhaps, at 660 pages, this otherwise dazzling book was in danger of becoming unliftable.
Yet the aspect of the human mind which we most urgently need an explanation for is the incredible juxtaposit ion of its capacity to accomplish with its faculty for ruin. We only become a mystery to ourselves when we do things we regret. Since few are yet in the business of reverse-engineering psychosis, this question does not yet concern those building artificial intelligences.
Pinker quotes the famous behaviourist B F Skinner: "The question is not whether machines think, but whether men do."
Dr Raj Persaud is consultant psychiatrist at London's Bethlem and Maudsley Hospitals and author of 'Staying Sane: How To Make Your Mind Work For You ' (Metro)