them a few years ago. What she discovered appalled her. Because virtually no studies had controlled for heritability, there was no proof of causation at all in any study. Not even lip service was being paid to this omission: correlation was being routinely presented as causation. Yet in each case, from behaviour genetics studies, there was new, strong evidence against what Rich Harris calls 'the nurture assumption'. Studies of the divorce rate of twins, for example, reveal that genetics accounts for about half of the variation in divorce rate, non-shared environmental factors for another half and shared home environment for nothing at all.1 In other words, you are no more likely to divorce if reared in a broken home than the average - unless your biological parents divorced. Studies of criminal records of adoptees in Denmark revealed a strong correlation with the criminal record of the biological parent and a very small correlation with the criminal record of the adopting parent — and even that vanished when controlled for peer-group effects, whereby the adopting parents were found to live in more, or less, criminal neighbourhoods according to whether they themselves were criminals.
Indeed, it is now clear that children probably have more non-genetic effect on parents than vice versa. As I argued in the chapter on chromosomes X and Y, it used to be conventional wisdom that distant fathers and over- protective mothers turn sons gay. It is now considered much more likely to be the reverse: perceiving that a son is not fully interested in masculine concerns, the father retreats; the mother compensates by being overprotective. Likewise, it is true that autistic children often have cold mothers; but this is an effect, not a cause: the mother, exhausted and dispirited by years of unre-warding attempts to break through to an autistic child, eventually gives up trying.
Rich Harris has systematically demolished the dogma that has lain, unchallenged, beneath twentieth-century social science: the assumption that parents shape the personality and culture of their children.
In Sigmund Freud's psychology, John Watson's behaviourism and 3 0 6 G E N O M E
Margaret Mead's anthropology, nurture-determinism by parents was never tested, only assumed. Yet the evidence, from twin studies, from the children of immigrants and from adoption studies, is now staring us in the face: people get their personalities from their genes and from their peers, not from their parents.1
In the 1970s, after the publication of E . O . Wilson's book
'Not in our genes!' It was at the time still just a plausible hypothesis to assert that genetic influences on behaviour were slight or non-existent. After twenty-five years of studies in behavioural genetics, that view is no longer tenable. Genes do influence behaviour.
Yet even after these discoveries, environment is still massively important - probably in total more important than genes in nearly all behaviours. But a remarkably small part in environmental influence is played by parental influence. This is not to deny that parents matter, or that children could do without them. Indeed, as Rich Harris observes, it is absurd to argue otherwise. Parents shape the home environment and a happy home environment is a good thing in its own right. You do not have to believe that happiness determines personality to agree that it is a good thing to have. But children do not seem to let the home environment influence their personality outside the home, nor to let it influence their personality in later life as an adult. Rich Harris makes the vital observation that we all keep the public and private zones of our lives separate and we do not necessarily take the lessons or the personality from one to the other. We easily 'code-switch' between them. Thus we acquire the language (in the case of immigrants) or accent of our peers, not our parents, for use in the rest of our lives. Culture is transmitted autonomously from each children's peer group to the next and not from parent to child - which is why, for example, the move towards greater adult sexual equality has had zero effect on willing sexual segregation in the playground. As every parent knows, children preF R E E W I L L 3 0 7
fer to imitate peers than parents. Psychology, like sociology and anthropology, has been dominated by those with a strong antipathy to genetic explanations; it can no longer sustain such ignorance.2
My point is not to rehearse the nature-nurture debate, which I explored in the chapter on chromosome 6, but to draw attention to the fact that even if the nurture assumption had proved true, it would not have reduced determinism one iota. As it is, by stressing the powerful influence that conformity to a peer group can have on personality, Rich Harris lays bare just how much more alarming social determinism is than genetic. It is brainwashing. Far from leaving room for free will, it rather diminishes it. A child who expresses her own (partly genetic) personality in defiance of her parents' or her siblings' pressures is at least obeying endogenous causality, not somebody else's.
So there is no escape from determinism by appealing to socialisa-tion. Either effects have causes or they do not. If I am timid because of something that happened to me when I was young, that event is no less deterministic than a gene for timidity. The greater mistake is not to equate determinism with genes, but to mistake determinism for inevitability. Said the three authors of
The reason the equation of determinism with fatalism is a fallacy is as follows. Suppose you are ill, but you reason that there is no point in calling the doctor because either you will recover, or you won't: in either case, a doctor is superfluous. But this overlooks the possibility that your recovery or lack thereof could be caused by your calling the doctor, or failure to do so. It follows that determinism implies nothing about what you can or cannot do. Determinism looks backwards to the causes of the present state, not forward to the consequences.
3 0 8 G E N O M E
Yet the myth persists that genetic determinism is a more implacable kind of fate than social determinism. As James Watson has put it, 'We talk about gene therapy as if it can change someone's fate, but you can also change someone's fate if you pay off their credit card.' The whole point of genetic knowledge is to remedy genetic defects with (mostly non-genetic) interventions. Far from the discoveries of genetic mutations leading to fatalism, I have already cited many examples where they have led to redoubled efforts to ameliorate their effects. As I pointed out in the chapter on chromosome 6, when dyslexia was belatedly recognised as a real, and possibly genetic, condition, the response of parents, teachers and governments was not fatalistic. Nobody said that because it was a genetic condition dyslexia was therefore incurable and from now on children diagnosed with dyslexia would be allowed to remain illiterate. Quite the reverse happened: remedial education for dyslexics was developed, with impressive results. Likewise, as I argued in the chapter on chromosome 11, even psychotherapists have found genetic explanations of shyness helpful in curing it. By reassuring shy people that their shyness is innate and 'real', it somehow helps them overcome it.
Nor does it make sense to argue that biological determinism threatens the case for political freedom. As Sam Brittan has argued,
'the opposite of freedom is coercion, not determinism.'4 We cherish political freedom because it allows us freedom of personal self-determination, not the other way around. Though we pay lip service to our love of free will, when the chips are down we cling to determinism to save us. In February 1994 an American named Stephen Mobley was convicted of the murder of a pizza-shop manager, John Collins, and sentenced to death. Appealing to have the sentence reduced to life imprisonment, his lawyers offered a genetic defence. Mobley came, they said, from a long
