Nowhere is the difficulty of separating science from politics, and the confusions of nature and nurture, more malign than in the study of differences among human groups. Older textbooks on race sooner or later come to the question, always treated with a certain prurience, of inherited differences in intelligence. That such dillm*uces existed and that they were inborn once seemed obvious. I.imucus himself classified humans as Homo sti^icus, thinking man. For the species as a whole, he could be no more pivusi- in his definition than Homo, nosce te ipsiwr. M.in, know thyself. His description of the different varieties ot humankind, in contrast, used behaviour as a character. Linnaeus' definition of an Asian, for example, was someone who was yellow, melancholic and flexible. Even forty years ago, racial stereotypes of the most predictable kind were still the norm.

Much of the work on inherited differences in intellect among races is contemptible and most of the rest is wrong. The wrong argument goes like this. Blacks do less well than whites on IQ tests, so that they are less intelligent. The IQ scores of parents and children are similar, so that differences in intelligence are controlled by genes. The difference between blacks and whites must therefore be set in DNA.

This argument is deceptively simple. It was once used in the USA as an excuse not to spend money on black education, and a variant of the theory, which sees poor rather than black children as victims of their genes, is employed in Britain by those who resent investment in state education (although, oddly enough, the most devoted hereditarians improve their children's environment by sending them to private schools). Simple as it may be, the argument is utterly false.

Whether IQ tests are an unbiased measure of intelligence is a matter for those who design them. The general consistency in the ability to move shapes around, or to do simple language puzzles and sums suggests a certain objectivity in the measure. The similarity of parents and children in their ability to do the test does not in itself say much, as families share the same environment as well as the same genes. It would be surprising if there were no genetic component in IQ variation. Many with low IQ suffer for genetic reasons, as several inborn illnesses manifest part of their effect by damaging the brain. Although normal variation in intelligence may not be related to such genes — after all, inborn blindness has nothing to do with variation in colour perception — a few inherited diseases do alter specific parts of the IQ mix. One, Williams syndrome {which involves the loss of a tiny section of chromosome), causes heart problems and a rather odd appearance; and a complete inability to deal with objects in space. Patients asked to draw a bicycle do a reasonable job with the wheels, the handlebars and the pedals — but they are scattered on the page. They find it impossible to arrange the parts into an image of the whole machine. However, their ability to speak or to do sums is not much affected.

This rare disease suggests that separate genes affect different parts of the IQ mix but, as always when using the abnormal to study the normal, says little about variation in the population as a whole. A mass of evidence from twins and adoption does suggest an inherited component to IQ. Indeed, a variant form of one gene involved in the growth of cells is frequent among children of very high intelligence (although it explains just a small part of the total variation). The gene involved helps move enzymes around inside cells and those of high intelligence may be more effective at burning sugar in the brain. Some claim that as much as seventy per cent of the variation in score within a population is due to diversity in its genes. This figure seems high, but can be accepted for the present. At first sight it looks like powerful evidence for the view that any racial differences in IQ must be set by biology.

In fact it has no relevance to understanding whether such differences — if they exist —;mⁱ inborn or acquired. Why this is so can be seen in another character. In the United States, the blood pressure of middle-aged black men is about fifteen points higher than that of whites. Twin and other studies show that about half the variation in blood pressure within a group is due to genetic variation, and some genes that influence the character have been tracked down. The figures for blood pressure look similar to those for IQ although in this case blacks come out with a higher score.

Doctors and educationists have a subtle difference in world-view when faced with such figures. Doctors are optimists. They concentrate on the environment, the fact that blacks smoke more and have poorer diets than do whites, and try to change it. In the USA, optimism has paid off and high blood pressure among blacks is less of a problem than before. Many educationists are less hopeful. To them, the existence of inherited variation in intelligence removes the point of trying to improve matters with changes in the environment. Blacks, they say, have worse genes. These cannot be altered, so that it is futile to spend money on better schools. Their theory has been proved wrong. Over the past thirty years the average IQ of Japanese children has risen to ten points higher than that of Americans. Not even the most radical hereditarian claims that this is due to a sudden burst of evolution in the Far East. Instead, the schools are getting better.

Both genetical and environmentalist views of blood pressure or IQ are naive. Characters like these are shaped by both gene.ind environment and it is meaningless to ask about genetic differences except in populations that live in the same conditions. I once did a simple experiment with a group of students. 1 divided them on the basis of hair colour. The fair-haired group were sent downstairs for coffee. The other set measured their own resting blood pressure. I then summoned the coffee-drinkers. As they had just run upstairs and were dosed with caffeine, their average score was higher than that of the dark-haired students. There was an association between blood pressure and hair colour.

Family studies show that much of the variation in resting blood pressure is due to inherited variation. To most of the students this proved the existence of a genetic difference in blood-pressure between dark and fair-haired people. Only when let into the simple secret of the differences in the experiences of each group was it obvious what is wrong in that claim. The students had made the same mistake as the educationists. High heritability combined with a difference between groups need not say anything about genes. The race and IQ story is, in the main, one of a dismal failure to understand basic biology.

A belief in heredity, rather like faith in predestination, is a good excuse for doing nothing. At least the environmentalist version can be used to try to improve matters. The genetkal view is often taken as a chance to blame the victim; to excuse injustice because it is determined by nature. In the last chapter of Daniel Deronda, biology wins. The hero returns to his ancestral roots and marries Mirah Mordecai, with the Cohen family in attendance. His admirer Gwendolen Harleth is left to console herself with the memory of her unlikeablc mate Henleigh Grand-court, drowned a few pages earlier. Determinism triumphs, which is convenient for the novelist. Fortunately, real life is more complicated than that. One of the most remarkable discoveries made by the new genetics has been to show how little we understand about the human condition that we did not know before.