Abstract

It is an observed fact that human populations differ in genetic composition. Some of the inherited diversity is due to combined effects of many genes. Although it would be interesting to know the magnitude and nature of the genetic contribution to some characters under polygenic control, such as intelligence or physique, environmental effects may be so great that no genetic analysis is possible—as Thoday has pointed out earlier in this symposium. With other polygenic characters, such as skin colour, the genetic component is more obvious but still difficult to analyse precisely. The number of genes involved, their frequency and dominance have not been established. This is one of the reasons why selective effects on such characters are not readily measured, although they probably exist.