The US Government licenses a heart drug to be used only by African-Americans. A pharmaceutical company trials a white-only anti-hepatitis drug. In a follow-up to the Human Genome Project, geneticists launch an international study to map genetic differences between races to help to provide data for treating diseases. Anthropologists develop a computer program to determine an individual's race from the shape of his skull. Commercial companies produce DNA kits to allow individuals to trace their racial ancestry. A genetic study claims that Jews are more intelligent because their history of moneylending and other financial occupations has favoured genes associated with cleverness. Another suggests that white Britons are genetically distinct and can trace their ancestry back to a few hundred Stone Age hunters who lived here some 14,000 years ago.

The scientific debate about race is back - and with a vengeance. Where once the idea of race was a scientific embarrassment, with most scientists dismissing racial differences as merely skin-deep, now it is becoming central to much scientific debate. Where once only the lunatic fringe embraced racial ideas, now they have become the currency of distinguished, mainstream thinkers. In genetics, anthropology, psychology and medicine the use of racial categories is becoming the norm in both research and practice. For the evolutionary psychologist Steven Pinker “the most dangerous idea of the next decade” will be the notion that races “may differ genetically in their average talents and temperaments”. Dangerous not because it is a myth but because it is scientifically true but politically inconvenient.

There are certainly real genetic differences between human populations. North Europeans, for instance, are more likely to suffer from cystic fibrosis than other groups. Tay-Sachs, a fatal disease of the central nervous system, particularly affects Ashkenazi Jews. Beta-blockers appear to be less effective on African-Americans than on those of European descent. There are more subtle differences, too. Africans are twice as likely to have a twin as Europeans, who are in turn twice as likely to do so as East Asians. The scientific study of these differences can help to unravel the roots of disease, develop new medicines and unpick the details of deep human history.

Such genetic differences are, however, not the same as racial differences. Race divides human beings into a small set of discrete groups, defined usually by skin colour, appearance or descent. Each race is seen as possessing a fixed set of traits and abilities and the differences between these groups is regarded as the defining feature of humanity. Yet none of these ideas make scientific sense.

But if the idea of race doesn't make scientific sense, why have scientists suddenly become so keen to talk about racial categories? They haven't. What they have done is become much more adept at defining genetic differences between populations. “If we look at enough genes,” Luca Luigi Cavalli-Sforza, the doyen of population biologists, observed more than a decade ago, “the genetic distance between Ithaca and Albany in New York or Pisa and Florence in Italy is most likely to be significant, and therefore scientifically proven.” Cavalli-Sforza added that while “the inhabitants of Ithaca and Albany might be disappointed to discover that they belong to separate races”, the “people in Pisa and Florence might be pleased that science had validated their ancient mutual distrust by demonstrating their genetic differences”.

Geneticists, in other words, can distinguish between all sorts of populations. Some of these distinctions are useful scientifically, some are not. Whether or not they are useful depends on the question we want to ask and the context in which we ask it.

Race has no scientific meaning because there is no such thing as a “natural” human population. Migration, intermarriage, war and conquest, forced assimilation, voluntary embrace of new or multiple identities (whether religious, cultural, national, ethnic or racial), social rules for defining populations such as the “one-drop rule” in America - these and many social other factors ensure that there are no such things as fixed natural populations.

Yet, many of the ways in which we customarily group people socially - by ethnicity, nationality, religious affiliation, geographic locality and so on - can have biological consequences. Members of such groups often show greater biologically relatedness than two randomly chosen individuals. Such groups may have been ghettoised by force or have chosen to self-segregate from other groups. Many have a distinct history, perhaps deriving from a small founder population or comprising an admixture of other definable groups. That is why groups such as “African American”, “people of Asian descent” and “Ashkenazi Jew” can be important in medical research. They are neither natural races, nor proper scientific categories, but they do provide a way into understanding some of the complexity of genetic distribution within the human species.

What we need therefore is a pragmatic approach to the question of scientific study of population differences. The trouble is, race is too politically charged an issue for such pragmatism. For some so-called race realists there is a macho element to defending the race concept: insisting that population differences are really race differences is, for them, a way of combating the scourge of political correctness. For their anti-racist critics, introducing population differences into genetic studies is to go down the road of eugenics and racial science.

I am taking part tomorrow in a debate on race and intelligence at the Science Museum. Last October, the Nobel laureate James Watson was due to have spoken there - until he gave vent to some incendiary comments, claiming that scientific research had revealed Africans to be less intelligent than whites. The museum decided that his comments had gone “beyond the point of acceptable debate”.

The row over Watson's comments shows much of what is wrong with the debate about race. Watson got his facts in a double helix. But why he was wrong can only be established through open debate. It was as legitimate for Watson to express his opinion as it is for me to express mine, even if his opinion is factually wrong, morally suspect and politically offensive. That is the essence of scientific debate.

Kenan Malik is the author of Strange Fruit: Why Both Sides are Wrong in the Race Debate, published last week

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