heredity

The passing down by genetic transmission of the characteristics of plants or animals from one generation to the next (‘like begetting like’). The idea of biologically transmitted similarities is an old one. However, ideas as to the means of this transmission and its malleability by environmental influences have changed. Present-day ideas are grounded in research on genetics (a term first coined in 1905 for the science of heredity) that has its origins in Mendel's classic studies cross-breeding peas. This and other research provided the missing link in Charles Darwin's theory of natural selection by specifying the mechanism through which species variation and similarity could occur.

The impact of such ideas on the study of human behaviour was considerable. Francis Galton, a cousin of Darwin, explored the role of heredity in accounting for individual differences in personality and intelligence . He also introduced the term eugenics for the body of knowledge that could be used to direct human evolution-an interventionist strategy that has remained highly controversial. Subsequent academic debate, juxtaposing heredity and environment in an exhaustive specification of causal factors, has continued the attempt to assess the relative contributions of genetics and environment in the causation of human characteristics and behaviour, with individual differences receiving much of the research attention. Twin studies, comparing monozygotic or MZ (identical) twins with dizygotic or DZ (non-identical) twins have been widely employed, although the methodological difficulties are considerable. However, whilst the attempt to quantify the genetic or environmental contribution to differences between individuals continues, there is increasing recognition that both genetics and environment are essential to all human behaviour. See also gene ; nature versus nurture debate ; sociobiology.