The true extent of scientific racism can best be grasped through its appeal to what is not normally seen as its constituency, namely to the liberals among scientists. This group consisted of the scientists who due to their political beliefs were made aware of the sinister character and consequences of racism, and provided a potential intellectual leadership to combat racism. However, their acquiescence to contemporary conventional views illustrates the difficulties in disentangling the racist web. At the same time, it suggests why once they broke with the consensus their critique was so effective: as insiders their views enjoyed the respectability both of science (the expert) and culture (the intellectual). This type of involved scientist was much more prevalent in Britain than in the United States, but recently scholarship on eugenics has claimed American counterparts in Herbert Spencer Jennings and Raymond Pearl. Jennings, a liberal, and Pearl, a conservative, fell short in their critique of racism as compared with the British group. In tracing in some detail the development of racial thought among these biologists, it is possible to delineate national as well as individual differences. As will be shown, a distinct political discourse shaped the scientific perceptions of race, and may account for the lack of American biologists among the intellectual leadership in the anti-racist campaign before World War II. The British group included J. B. S. Haldane, Lancelot Hogben, Lionel Penrose and Julian Huxley, the last of whom changed his views on race most dramatically.