Biodemography and Darwinian theory

Lesley Newson, University of California, Davis
Peter Richerson, University of California, Davis

Theory in biodemography must reflect the theoretical underpinnings of biology. Biodemographers therefore need to explain why most contemporary humans do not strive to maximize their “inclusive fitness”. Human behavioural ecologists have shown that reproductive behaviour in traditional societies is consistent with Darwinian theory but the cultural changes associated with modernization include a progressive abandonment of norms that encourage efficient conversion of resources into offspring. Our evidence suggests that this is the result of a change in the composition of human communities. Human behaviour is regulated by cultural norms which are generated by social interaction within communities. This uniquely human behaviour evolved in communities in which a high proportion of social interaction was between kin, who have an interest in encouraging each other to make evolutionarily optimal reproductive decisions. In modern communities a smaller proportion of interaction is between kin so encouragement is reduced allowing norms to become increasingly less pro-natal.