Positive feedback relationship

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It is admittedly difficult to prove that mankind has changed biologically since, let us say, the days of the ancient Greeks and Romans, if by "proof" you mean demonstration of sizeable gene differences. We cannot test the genes of Pericles or Caesar or their contemporaries. But neither was Darwin able to "prove" organic evolution in this sense. The evidence is indirect, inferential, but nevertheless, I think, conclusive.

Paradoxically, it is precisely because we know that mankind changes so greatly culturally that we can be so confident that it changes to some extent also genetically. When the environment changes, the only other necessary condition for the occurrence of genetic evolutionary change can be defined. This is the presence in human popluations of genetic variants, some of which confer upon their carriers a higher fitness....

Despite all the inadequacies of our present knowledge of human genetics, this can scarcely be doubted. What is more, since the environment in which man lives is in the first place his sociocultural environment, the genetic changes induced by culture must affect man's fitness for culture and hence may affect culture. The process thus becomes self-sustaining.

Biological changes increase the fitness for, and the dependence of their carriers on culture, and therefore stimulate cultural developments; cultural developments in turn instigate further genetic changes. This amounts to a positive feedback relationship between the cultural and the biological evolutions. The positive feedback explains the great evolutionary change, so great that it creates the illusion of an unbridgeable gap between our animal ancestors and ourselves....

Dobzhansky T. 1963. Anthropology and the natural sciences - The problem of human evolution. Curr Anthropol 4:138+146-148

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