In his exceptionally insightful book, Racism: A Short History, Stanford University historian George M. Fredrickson notes the paradox that notions of human equality were the necessary precondition to the emergence of racism. If a society is premised on an assumption of inequality, producing an accepted hierarchy -- one unquestioned even by those relegated to its nadir -- then there is no need to locate the cause of the underlings' position in some specific characteristic on their part that makes them less worthy than others.

However, as societies have become increasingly committed to the belief in freedom and equality -- as once revolutionary ideas about equal rights for all have become more widespread, especially in the West -- then those groups that are systematically denied these entitlements are claimed to possess what Fredrickson calls "some extraordinary deficiency that makes them less than fully human". That is, racism arose as a result of the contradiction between egalitarian principles coupled with the exclusionary treatment of specific ethnic groups: the rejection of organically hierarchical societies brought with it the implied necessity to account for the fact that some groups were subjected to servitude, enforced separation from the rest of society, or ghettoization.

Beginning around the end of the eighteenth century, as Enlightenment rationalism replaced faith and superstition as the source of authority, the pronouncements of science became the preferred method for reconciling the difference between principle and practice. In societies in which there has been systematic discrimination against specific racial groups, inevitably it has been accompanied by attempts to justify such policies on scientific grounds.

Broadly speaking, there have been three types of scientific explanations offered in putative support for racial discrimination, each of them having a lengthy history. One approach has been to claim that there are biological dangers involved in racial interbreeding. Indeed, it was precisely on the basis of this belief that in the United States and South Africa for many years there were statutory prohibitions against intermarriage. The first supposed evidence for this conclusion was provided in the mid-nineteenth century primarily by physicians, who claimed that, as a result of their mixed blood, "mulattoes" were considerably more susceptible to disease than either of their parents and thus exceptionally short-lived. In addition, were persons of mixed race to intermarry, according to leading anthropologists at the time, they became progressively less fertile, eventually becoming completely sterile.

In the early twentieth century, shortly after the scientific community's discovery of Gregor Mendel's work led to a new, exciting branch of biology, geneticists warned that the intermarriage of "far apart" races could produce what they called genetic "disharmonies". Charles Benedict Davenport, a world renowned researcher at the time, observed, for example, that if a member of a tall race, such as the Scots, should mate with a member of a small race, such as the Southern Italians, their offspring could inherit the genes for large internal organs from one parent and for small stature from the other, resulting in viscera that would be too large for the frame. Naturally these claims were not tenable for long, but they were soon replaced by assertions less easily disprovable, as some social scientists insisted that the children of mixed race parentage were morally and intellectually inferior to either of the parents.

Although belief in such genetic mismatches was once fairly widespread within the scientific community and cited specifically to rationalize various racially oppressive policies, this notion now enjoys far less credibility. However, while there has been absolutely no evidence that racial interbreeding can produce a disharmony of any kind, warnings of some kind of genetic discord are still far from entirely extinct. Only a few years ago, Glayde Whitney, a prominent geneticist and former President of the Behavior Genetics Association, claimed that the intermarriage of "distant races" could produce a harmful genetic mixture in offspring, citing the wide range of health problems afflicting African Americans and their high infant death rate as examples of the effects of "hybrid incompatibilities" caused by white genes that were undetected due to the "one drop" convention defining all "hybrids" as blacks. Unsurprisingly, he was also a regular speaker before neo-Nazi groups and, in an address to a convention of holocaust deniers, blamed Jews for a conspiracy to weaken whites by persuading them to extend political equality to blacks.Another trend in the scientific justification of racial discrimination has been the claim that prejudice is a natural and indeed an essential phenomenon necessary for the evolutionary process to be effective by ensuring the integrity of gene pools. In this view, evolution exerts its selective effect not on individuals but on groups, which makes it necessary for races to be kept separate from each other and relatively homogeneous if there is to be evolutionary progress. One anthropologist who adheres to this belief refers to the tendency to "distrust and repel" members of other races as a natural part of the human personality and one of the basic pillars of civilization.

Finally, the most common way in which science has been used to support racial discrimination is through pronouncements that some groups are systematically less well endowed than others in important cognitive or behavioural traits. This is not to say that there may be no group differences in these traits, but rather that at this point there are no clear conclusions, which in any event would be irrelevant to issues of social and political equality. Nevertheless, there is again a long history of the use of such claims for oppressive purposes. For the first quarter of the twentieth century, there was particular concern over the results of early intelligence tests, which supposedly demonstrated that Southern and Eastern Europeans were not only intellectually inferior to their Northern counterparts, but were also unfit for self-rule. Some of the most important scientists of the time explained that Nordics, characterized as they were by greater self-assertiveness and determination, as well as intelligence, were destined by their genetic nature to rule over other races. In the last half century, the controversy over intellectual and moral traits has focused primarily on the differences between blacks and other races, which were often cited by those seeking to preserve white minority rule in South Africa and legal segregation in the United States.

At present, the most well known researcher to emphasize the importance of racial differences is Canadian psychologist J. Philippe Rushton, the author of Race, Evolution, and Behavior: A Life History Perspective, which was distributed unsolicited in an abridged version to tens of thousands of social scientists in an unsubtle attempt to influence both fellow scientists and public opinion. In the preface to the abridged paperback, Rushton promised to explain why races differ in crime rates, learning ability and AIDS prevalence. In the ensuing account, he asserted that the behaviour of blacks, whether in Africa or the diaspora, reflected what he called a "basic law of evolution", in which reproductive strategy was linked to intellectual development, such that the more advanced the latter, the fewer the number of offspring and the greater the investment of time and effort in the care of each of them. Thus, he declared, in comparison to Caucasians and Asians, blacks tended to be more sexually active and aggressive, while less intelligent and less capable of self-control, complex social organization and family stability. Like Glayde Whitney, Rushton too has been a favourite speaker at conventions of organizations dedicated to political policies that would encode white supremacy officially into law.

In the aftermath of the Second World War, two conferences of internationally recognized scientists, held by the United Nations, Educational, Scientific and Cultural Organization (UNESCO), issued statements about race. Although there were some slight differences in their observations about the possibility of innate differences, both groups agreed that equality as an ethical principle concerning the rights to be enjoyed by all members of a society was not predicated on any scientific conclusion about racial characteristics. This position should still inform our thinking about race and science. Although the strains of thought discussed in this article do not have widespread support among contemporary scientists, whether they are appropriate issues for scientific pursuit is beside the point. Such claims, scientifically bogus or valid, should be utterly irrelevant to the entitlements enshrined in the UN Universal Declaration of Human Rights.