The Inheritance of Intelligence and Its Social Implications

It is argued that the wide differences between the intellectual achievements of children from different socio‐economic classes are due not only to environmental but also to genetic differences. In spite of the marked improvement in social conditions during recent years, the differences between the average levels for each class remain much the same as before the war. The distribution of genetic differences displays two significant characteristics: ( a ) the average level of children from the lower occupational groups is lower than that of the others, but ( b ) owing to their numbers and the wide range of individual variation, they provide a larger number of able children than the higher groups. A multifactorial process of inheritance combined with the effects of social mobility would adequately account for all the important features observed. Recent critics have questioned the validity of this explanation, and in particular have doubted the evidence for mental inheritance (notably that which rests on the study of identical twins). An attempt is made to answer their objections in the light of newer evidence now available.