Surveys in the developed world show that most people believe nurture has more influence than nature on what we are like.

As a teacher, you are particularly likely to believe this, probably citing some mixture of parenting, social class background, gender socialisation, and - for heaven’s sake - even the quality of your teaching and particular school. And yet, the chances are that you also tend to the view that it’s not all environment, that genes are important, that it’s always “a bit of both”.

It seems like common sense, especially if you have had children yourself.

You probably have come to feel that some of their traits (the undesirable ones, natch) are down to genes (though, of course, some are due to your partner’s poor parenting habits as well).

Well, think again: the bit of both theory does not stand up. The evidence nearly always cited to support it is studies of identical twins. Their reliability is questionable, but even if you take the results as true, contrary to what you may have read in the press or seen on TV, they demonstrate that great swathes of our psychology come out only 10-30 per cent genetic - hardly “a bit of both”. Indeed, many crucial aspects have no heritability at all, such as our relationship patterns, whom we fancy or the propensity to criminal violence.

Minor depression, which is actually anything but minor, and neurosis account for two thirds of mental illness, yet they hover around the 20 per cent mark at most, ie, most people’s emotional problems are largely not genetic.

It’s a similar picture for most cognitive abilities and personality traits.

Memory is 32 per cent genetic, creativity is 25 per cent, exceptional achievement in almost all fields appears to have virtually no genetic influence - the way that Sharapova’s or Beckham’s parents hot-housed them largely explains their talents. Sociability, Conservatism and religiosity are around the 30 per cent mark.

The only universal characteristic to come out half heritable is adult intelligence. Interestingly, children’s is less, at around 30 per cent.

This is believed to reflect the extent to which genes override parental influences as we become more independent. Apart from IQ, to find a “bit of both” you have to turn to rare mental illnesses such as schizophrenia, manic depression and autism.

But even in these cases, nurture is often critical. Suppose 100 schizophrenics have got an identical twin. On average, 48 of the twins will also have the illness. This suggests genes can be important, but when you stop to think, it also shows that in 52 out of 100 cases, genes could not have been the illness’s cause, because both twins have exactly the same inheritance.

The vital role of parental care was proved in a Finnish study. It compared boys who were adopted at a young age, because their mothers were schizophrenic, with adoptees of mothers without the illness. Having an increased genetic risk only mattered if the adoptive care was disturbing.

If the care was good, the boy with a schizophrenic biological mother was at no greater risk than one whose biological mother had not suffered the illness. Whether this reading of the evidence is correct is of more than academic interest. It affects how we bring up our children, whether or not you as a teacher regard the fact that a pupil is “thick” as an unchangeable destiny and what policies a government adopts.

People who believe genes are crucial are more likely to subscribe to right-wing political credos. In contending that educational and welfare spending were largely a waste of money, many Tories in the 1980s were guided by the American political scientist Charles Murray, who maintained that genes were critical.

The implication of his work was that you might just as well try to change the colour of their eyes by talking to the poor (especially the black poor) as try to make them more intelligent by giving them extra education.

Blair’s claim that he wanted a society in which everyone’s “God-given talents” could flourish rather gave the game away as to the neo-conservative bent of his core thinking - if talents are God-given (genetic) at birth, why bother with all that spending on education, education, education?

Even if you take the results of twin studies at face value, they do not support the “bit of both” view, which is good news for teachers who see it as their job to try and change the trajectory of their pupils’ lives. What is more, that assumes twin studies - the bedrock of the genetic case - are reliable, which, as I shall explain next week, they most definitely are not Oliver James is the author of Affluenza - How to be successful and stay sane. The second edition of his They F*** You Up: How to survive family life is out now

References

For heritability estimates see Plomin, R, 1990, Nature and Nurture: An introduction to Behavioural Genetics.

See also appendix 3, James, OW, They F*** You Up.

The Finnish study: Wahlberg, KE et al, 1997, American Journal of Psychiatry, 154, 355-62.

Murray, C, 1981, Losing Ground and Murray, C, 2000, The genetics of the Right, Prospect, April.