Cultural versus biological inheritance: phenotypic transmission from parents to children. (A theory of the effect of parental phenotypes on children's phenotypes).

The foundations of biometrical genetics were first laid in a famous paper by R. A. Fisher [1]. Since that time a considerable amount of literature has accumulated, the book by Mather and Jinks [2] being the most recent summary. In most treatments, the mode of transmission of nonbiological contributions to the phenotype has not been specified in detail. An interesting exception is an analysis of adoption studies and IQ by S. Wright in 1931 [3], in which a direct inheritance of "environmental factors" over 1 generation has been postulated and found (by path coefficient analysis) to be of some magnitude. When the parents' phenotypes affect the phenotype of their children directly, a new mode of inheritance arises which operates side by side with strictly biological inheritance (through the DNA) and may be difficult to distinguish from it. This transmission is entirely phenotypic. Under certain conditions its importance relative to purely biological inheritance is not negligible, and justifies its theoretical investigation. Such a mode of inheritance bypasses DNA and will be more relevant for those characters which develop through a learning process. Parents' participation in teaching is especially important in the earlier years of development, perhaps more so in the less developed areas of the world, and those traits that are learned during the first period of life are more likely to show phenotypic transmission from parent to child. Clearly, effects of this kind are more likely to exist for traits where "cultural" transmission is of importance. In general terms, cultural transmission occurs when parents and other members of the group may influence a child's behavior. A preliminary analysis of the consequences of cultural effects of members of the group,