Concerned to reconstruct past ideas, historians must approach the generation that held them as the anthropologist approaches an alien culture. They must, that is, be prepared at the start to find that natives speak a different language and map experience into different categories from those they themselves bring from home. And they must take as their object the discovery of those categories and the assimilation of the corresponding language.

Geneticists believe that anthropologists have decided what a race is. Ethnologists assume that their classifications embody principles which genetic science has proved correct. Politicians believe that their prejudices have the sanction of genetic laws and the findings of physical anthropology to sustain them.