Darwin on the mind

It is well known that to write a best-selling book about evolution it helps to be called Steven. When Professor Steven Pinker's last book, The Language Instinct, was short-listed for the Rhone Poulenc prize for science books in 1995, it immediately became the favourite: the three previous winners were Professors Steven Rose, Stephen Jay Gould and Steve Jones.

In the event, Pinker did not win the prize; and some think the reason was that he is not a true Steven. The other three Stev(ph)ens respect a hallowed tradition: that evolution is about bodies, not minds. The human mind is studied by people who know nothing about evolution. Charles Darwin tried to understand the mind through evolutionary theory, but after his death biologists retreated from the attempt. In the 20th century, the mind became the province of Freudians, behaviourists and sociologists. All of them believed, in one way or another, that the mind is made by outside influences, not innate structure; that psychology is the product of society, not vice versa. They put up large signs: "Keep out: biologists will be persecuted."

The tradition held for most of this century. Well-behaved biologists enforced it as vigorously as social scientists, vilifying those among their tribe who stepped over the boundary-such as the hapless EO Wilson, a Harvard ant specialist, who in 1975 allowed some incautious speculation about human beings into his book on social behaviour in animals, Sociobiology. Such trespassers are accused of reductionism, essentialism, determinism, even Nazism. Most get the message and stick to beetles.



But a few biologists have persevered, and have been encouraged recently by one or two social scientists. In Britain, the philosopher Helena Cronin at the LSE has championed Darwinian explanations of the mind, as has the sociologist Garry Runciman. In psychology the stage is now set for a replay of the old Victorian battle between evolution (man is an animal) and exceptionalism (man is different).

Modern evolutionary theory now uses an argument once used against it: the argument from design. It was once an important strand of theological thinking that animals were at least as complex as watches and therefore must have been made by entities at least as clever as watchmakers. Ergo god. Today, the dominant idea in evolutionary theory is "adaptationism," which turns this on its head. Where you come across a complex biological machine, such as the human eye, the chances are that it was designed to do a job-but the designer was natural selection, not god. The more complex the organ, the more legitimate it is to assign to it a designed "function."

Yet until recently the dominant idea in psycho-logy has been that the human brain-the most complex biological machine on the planet-is not designed for specific jobs, but is a general purpose device at the whim of every cultural or social breeze. Whoops, this one had a deprived upbringing, so it's neurotic; whoops, that one was born an Inuit, so its thought is conditioned by a language rich in words for snow; whoops, this one was born a communist, so it puts the social good ahead of self-interest.

This kind of environmental determinism rests on the last vestige of the argument that human beings are different from animals: human beings learn, and transmit ideas culturally; animals do not. Whereas animals have instincts, human beings have minds designed only to absorb the culture.

But there's the rub. If the mind is designed to absorb the culture, then it needs an innate structure to do so. The central theme of Pinker's work is that the ability to learn is itself an instinct. He argues in The Language Instinct, like Noam Chomsky before him, that there are universal grammatical principles that underlie all human languages, that human language develops without being actively "taught" and that we human beings have an instinct for language that other animals do not share. Chomsky refuses to accept that this implies that language "evolved" by natural selection-he sees it instead as a fortunate by-product of the size of the human brain. Pinker disagrees. He argues that human language has all the hallmarks of an innate, evolved organ designed by natural selection for the purpose of learning a language, just as the hand is an organ designed for the purpose of learning manipulation.

Pinker goes further. Having trespassed into language, he now marches boldly into the rest of the brain, leaving nothing untouched by evolutionary logic. In his new book How the Mind Works (The Penguin Press), even music and the emotions get the evolutionary treatment. The 20th century compact is truly broken; Darwin's assault is resumed. If Pinker's view prevails, no psychologist will be equipped to understand the human brain until he or she has taken a course in evolutionary psychology.

Pinker is professor of psychology at the Massachusetts Institute of Technology-which explains one of two strands which make up his thinking. A British professor named David Marr, who died in 1982 in his 30s, founded a school of thought at MIT known as natural computation. He argued that the way to understand the brain was to reverse-engineer it (this was MIT, after all) and that if you did so, you found something very different from a general purpose computer responding impartially to inputs from the environment. You found a device exquisitely designed to process specified information from the world.

For example, in order to see, our eyes do not simply project images on to the back of the brain; the brain takes the eye's image and dismantles it, extracting information about contrast, edges, shading, stereo and movement, to recreate in the brain a best guess about what the scene before us contains. That guess is then reproduced as a mental image. That is why optical illusions confuse us, and why a painting can appear to have depth and perspective.

Modern computational psychology sees the brain as a collection of such modules, each designed to do a job. But who designed them? This is where the other strand of Pinker's thinking comes in. In the early 1960s, there was a revolution in the study of animal behaviour. Out went all the old species-centred thinking (aggression is ritualised to preserve the species, and the like); in came gene-centred thinking. A worker ant slaves away on behalf of its queen, not for itself but for its genes. A human mother sacrifices much for her children; not because it is good for her, but because it suits her genes.

Bodies and societies are means to an end for competing genes seeking to ensure their own perpetuation. Do not seek to understand human behaviour as modern self-interest, as economists have done; seek instead what made genetic sense in the ancestral environment of African hunter-gatherers.

This revolution, focused on animals, was led by George Williams, Bill Hamilton and Robert Trivers; it found its amanuensis in Richard Dawkins. But it was two husband-and-wife teams who turned its full force upon the human mind: Martin Daly and Margo Wilson in Canada; and John Tooby and Leda Cosmides in California. They started with the observation that if human behaviour is shaped by evolution, we would expect to find universal human behaviours-ways of behaving that vary little in different cultures.

Sure enough, after a decade of studies it turns out that human patterns of seduction, attraction, violence, homicide and emotional expression are basically the same everywhere. A smile means the same thing in New Guinea and New York. Men like beautiful women and women like rich men everywhere-even in places and subcultures where women are richer than men. Even ritual, religion, language, music and social organisation show remarkable common features.

This is not to deny that human behaviour varies with locality, experience and tradition. But there may also be common undercurrents so familiar to us that we do not notice them. Seeking human universality does not mean accepting that all human beings are the same. We could be equipped with universal instincts to become different according to different circumstances. This has been suggested by Frank Sulloway in his book Born to Rebel. Sulloway argues that birth order affects personality-eldest siblings being conservative and responsible compared with their more rebellious younger sibs. The instinct here is equipped with an "if-then routine": if eldest, develop this way; if younger, develop that way.

Indeed, taking Sulloway's point further, I have argued that human beings are unique among animals in the way they specialise as adults in being good at some things rather than others, a feature of our minds which probably evolved to suit the human reliance on a social division of labour. Thus nurture reinforces nature; it is not its opposite. People may be born with an instinct to practise what they enjoy doing. Those of a musical nature would seek out musical nurture; those of a sporting nature seek out sporting nurture. The innate bit is not the small spark of talent, but the desire to fan it into flames.

Critics of this approach-known as evolutionary psychology-argue that it is genetically determinist: it assumes that we are pre-programmed automata, lacking in free will and in the ability to learn. But as Pinker retorts in his new book, this is simply a misunderstanding based on the old, discredited dichotomy view of nature and nurture. It is, he says, "a colossal mistake" to frame the issue so that learning and instinct are seen as opposites: "It falls in the category of ideas that are so bad they are not even wrong."

He uses the analogy of a computer. If somebody boasted to you that his computer was equipped with all sorts of bells and whistles-hard drive, CD-Rom, modem, word-processor, spellchecker-you would not say: "Oh, so it's pre-programmed and does the same thing whatever you type in, does it?" The human mind is a computer equipped with lots of good accessories not available to chimpanzees (such as a language instinct) but the extra accessories enable the brain to learn more, not less. Learning, says Pinker, "does not happen by magic. It is made possible by innate machinery designed to do the learning."

Nor does evolutionary psychology undermine free will. All determinism does that. The idea that we are the products of our environments is just as antithetical to free will as evolutionary thinking. It says that our behaviour has an external cause. Evolutionary psychology, by arguing that our personalities are remarkably robust in the face of parental and societal influences, actually rescues free will from the rather scary brain-washing ideas of environmental determinists. Seventy years of communism did not change Russian human nature (thank goodness).

Indeed, because our brains are full of contradictory instincts, it is nonsense to conclude that we are pre-programmed to take a narrow view of self-interest. "People throughout history have invented technologies that turn one part of the mind against another," says Pinker, "and eke increments of civility from a human nature that was not selected for niceness." Conflict is a universal human instinct, but so is peacemaking.

Those who have espoused evolutionary psychology are often accused of condoning or excusing human behaviour. They are said to be justifying prejudice, promiscuity or violence. This is an odd accusation, because it is never levelled at the rival theories of environmental determinists. We do not say to Freudians: you condone incest by saying that Oedipal desires are natural; or to behaviourists, who argue that child abuse begets child abuse: by explaining it you excuse it. Why should genes be different?

There is, as John Tooby put it to me once, a lot of burden-tennis going on in psychology. The evolutionary psychologists believe the burden of proof is in their court, and they would like to lob it back on to the social theorists. An evolutionary theory of human behaviour is required to produce scientific evidence, whereas the flimsiest theory of social causation is widely repeated on the basis of a few anecdotes alone.

For example, we now know that although the killing of children is extremely rare, step-parents are 60 times more likely to murder children than biological parents. We know this, not because the statistics revealed it, but because it was a direct prediction of evolutionary theory; Daly and Wilson dug out the statistics to test the proposition.

As this example shows, whether Pinker is right is in the end an empirical issue; and the evidence so far supports him. Studies of identical twins reared apart, started by Freudians anxious to prove that people's personalities are shaped by the family which rears them, have provided dramatic evidence for the exact opposite: that variation in personality is, roughly speaking, half genes and half peer pressure, with family contributing at most 5 per cent of the recipe (as Jerome Burne argued in the January issue of Prospect).

Such a result was predicted by the evolutionary theorist Robert Trivers. Trivers's theory of parent-offspring conflict is based entirely on selfish-gene reasoning; from it he concluded that human beings would be designed to be resistant to parental influences on personality, because parental care is a scarce resource in which parents and children have a different genetic interest. Adolescent crises can be seen as adaptations in children to extract resources and resist influences from parents. Or take incest-a clear test case of the two approaches to human behaviour. Freud argued that we have incestuous desires which we overcome with social taboos because inbreeding is dangerous. Edward Westermarck, his rival, argued that we have an instinct to find sex unattractive with those whom we knew as children. The evidence now supports Westermarck's theory. Two siblings separated at birth often find each other sexually attractive if they meet as adults. Two unrelated individuals reared together (in Taiwan, children were sometimes reared together with their future spouses) find it hard to consummate or maintain a marriage.

Pinker borrows from this canon of evolutionary psychology studies. They have rarely been gathered in one place, or expressed with such wit, eloquence or subtlety. His exposition of the evolutionary explanation of emotions, for example, is the most satisfying account available. Emotions, in Pinker's parlance, are doomsday machines. The doomsday machine which destroys the world at the end of the film Dr Strangelove is a gigantic bomb designed to explode if the Soviet Union is attacked, and impossible to countermand. It is the ultimate deterrent (although, as Strangelove observes to the Soviet ambassador, the whole point is lost if its existence is kept a secret). Our emotions are doomsday machines-we cannot control them, so they act as guarantors of any threats, promises or offers we make. They are deliberately designed to be out of control of the intellect. Guilt and shame make contracts enforceable; love makes marriage durable; anger makes threats credible.

As Pinker wryly observes, this is the very opposite of the Romantic model of the emotions, which sees them as our pure, instinctive, creative side, as enemies of the intellect. The intellect needs the emotions in such a complex social creature as the human being; and it needs a firewall between itself and the emotions, the better to make them credible. Although it is not easy to see how to test the doomsday-machine theory, it has at least as much supporting evidence as any rival theory of the emotions.

There is a temptation in evolutionary psychology to slip into telling what Stephen Jay Gould has called just-so stories: inventing ancestral functions for all behaviour. Maybe people sneeze because their noses itch, not because it mimics the sound of a wildebeest calf and helps the hunter to attract his prey. Pinker is careful not to fall into this trap. He argues that a complex mental architecture, like language or emotion, requires an evolutionary explanation. But not all behaviour is like this. Much of it is the by-product, rather than the function, of our instincts.

For example, Pinker tries to explain music, art, drug abuse and pornography not by arguing that we have instincts to enjoy them, but that they are pleasure technologies, crafted to appeal to our various pre-existing instincts and senses. That is, we do not have an instinct to enjoy music, but we have instincts that music has been designed to appeal to. We do not have an instinct to enjoy strawberry cheesecake, but we have an instinct to enjoy sweet, ripe fruit, the feel of fats in the mouth and the coolness of fresh water. All these things were scarce and desirable in the African savannah where we evolved.

Music, pornography, art, James Bond movies and heroin are all in their different ways forms of virtual strawberry cheesecake. Phobias are at the other extreme: things we have specific instincts to dislike. To be afraid of heights, snakes, spiders, storms, blood, strangers, deep water and large carnivores made good sense in the African Pleistocene. Things which are dangerous now, such as cars, electrical sockets and guns, we rarely have phobias about. A snake hits the button of our instincts, a pistol does not.

Nobody will accuse Pinker of modesty in his ambitions. But having served his apprenticeship at the coalface of linguistics and come up with a convincing case history of evolutionary psychology, he has earned the right to write a book called How the Mind Works. For those interested in consciousness and free will, however, he turns suddenly modest at the end.

Just because evolutionary psychology can explain much about the human mind, it does not follow that it can explain everything. Indeed, it could be used to argue the very opposite: that some things will forever be beyond our comprehension. The reason is that our brains were designed to deal with the social and practical issues of life on the savannah. Any capacity they have for abstract thought and logical reasoning is a fortunate by-product of that design.

"Our minds evolved by natural selection to solve problems that were life-and-death matters to our ancestors, not to commune with correctness or to answer any question we are capable of asking. We cannot hold ten thousand words in short-term memory. We cannot see in ultraviolet light... And perhaps we cannot solve conundrums like free will."