Earlier this month, James Watson, the geneticist who shared the 1962 Nobel prize for his part in the co-discovery of DNA, created waves in the scientific community and beyond for his view that it was an illusion to believe that “equal powers of reason” were shared across racial groups.

It was not the first time that Watson provoked controversy with his “scientific” comments. He once suggested that there was a biochemical link between exposure to sunlight and sexual urges. “That’s why you have Latin lovers,” he said. “You’ve never heard of an English lover. Only an English patient.”

There was also a scientific link between thinness and ambition. It’s the reason why “whenever you interview fat people, you feel bad, because you know you’re not going to hire them.”

It was, however, his recent remarks that drew the most widespread and hostile reaction. In an interview with The (London) Sunday Times, Watson said he was “inherently gloomy about the prospect of Africa” and its people because “all our social policies are based on the fact that their intelligence is the same as ours—whereas all the testing says not really.”

We naturally wish, he continued, “that all human beings were equal, but people who have to deal with black employees find this not to be true.”

Watson was forced to resign as director of the Cold Spring Harbor Laboratory on Long Island, an institute considered a world leader in research into cancer and genetics, and his comments continue to fuel denunciation. He is, however, only the latest in a group of scientists in the late 20th and early 21st centuries to posit genetic differences between blacks and whites that condemn blacks in perpetuity to being inferior.

In a 1969 article in The Harvard Educational Review, Arthur Jensen, a psychologist at the University of California, Berkeley, maintained that a 15-point spread in IQ between blacks and whites was due to genetic differences that could never be erased.

In the sixties also, William Shockley, a physicist at Stanford University, advocated voluntary sterilisation as the way to deal with blacks who had an IQ of less than 100. He and Jensen agreed that such “eugenic foresight,” and not social engineering, was the only real solution to the social problems bred by low IQ.

In 1994, Richard Herrnstein and Charles Murray published The Bell Curve, a work that echoed the familiar assertions of racial inferiority. And more recently, in a series of online articles on “human nature” in Slate, William Saletan defended basically similar views.

The findings of these “hereditarians,” as they are called, have been challenged as untrustworthy on scientific grounds. Herrnstein and Murray, for instance, were shown to have not only used statistics selectively but to have manipulated them to prove that certain programmes, eg affirmative action and Head Start (a programme promoting the social and cognitive development of children), do not work, while ignoring data from other studies that suggested otherwise.

More importantly, beyond such dishonesty, in terms of strict evidence, no set of genes or gene markers has been conclusively linked to the development of intelligence. There has also been no evidence to substantiate the claim of a link between brain size and intelligence.

Blacks are said to have smaller brains than whites, but the brain size between men and women is greater. Yet men and women, on average, score the same on IQ tests. A group of people in Ecuador has a genetic anomaly that produces extremely small head sizes—and thus brain sizes. Yet their intelligence is as high as that of their unaffected relatives.

Hereditarians pay no attention to environmental influences, and yet common sense tells us that nature and nurture are both constituents of who we are and what we become. No one knows exactly where the influence of either begins and ends. All we see at any given time is their interaction.

Yet science today—perhaps because the genetic bias keeps recurring—increasingly demonstrates that environment can markedly influence IQ.

The so-called Flynn Effect, for instance, named after James Flynn, a philosopher and IQ researcher in New Zealand, has established that in the West, IQ increased substantially from 1947 to 2002. Our genes alone could not have changed over such a brief period to account for the shift; it must have included the effects of powerful social factors. And if such factors could produce changes over time for the population as a whole, they could also produce big differences between subpopulations at any given time.

In fact, researches also know that the IQ difference between black and white 12-year-olds in the US dropped to 9.5 from 15 points in the last 30 years, a period that was socially more favourable to blacks than the preceding era.

Many more researchers than formerly have taken issue with the conventional approach in which a single number on a linear scale defines the learning potential of an individual. In fact, in his book The Mismeasure of Man, Stephen Jay Gould, the late Harvard palaeontologist, had long questioned the pretentious pronouncements and publications of such scientists as Watson, based on the prevailing approach.

In the words of one critic, Gould skewered “the abstraction of intelligence as a single entity, its location within the brain, its quantification as one number for each individual, and the use of these numbers to rank people in a single series of worthiness, invariably to find that oppressed and disadvantaged groups—races, classes, or sexes—are innately inferior and deserve their status.”

Psychologists who like Gould have questioned the conventional methodology, have developed alternative models that attempt to expand the definition of intelligence to include a broader spectrum of abilities. Such models have explored capacities such as creativity, social intelligence, and commonsense as keys to human adaptation. They include Howard Gardner’s Theory of Multiple Intelligences, Robert Steinberg’s Triarchic Mind, and Daniel Goleman’s Emotional Intelligence.

IQ testing was from its inception tainted not just with bias but with the evil of racist eugenics. Originally designed by French psychologist Alfred Binet in 1905 to identify students who would need help in school (not as an overall measure of cognitive ability), the method came to be regarded as having laid the foundations of modern intelligence-testing.

Lewis Terman, another scientist at Stanford, adapted Binet’s scale and hoped it would attract the attention of governments to the “tens of thousands of defectives” who should be kept from breeding. The area is still saddled with the continuing effects of that pernicious impulse.