Genetic variation and social structure: a case-study from Africa

Understanding the relations between social and biological factors in determining the evolution of human populations is one of the principal aims of bio-anthropological research. The recent introduction of unilinearly transmitted polymorphisms of mitochondrial DNA and Y-chromosome has disclosed new possibilities for the study of bio-cultural evolutionary processes. In this communication, I present a study on the relationships between social structure and genetic variation in sub-Saharan Africa based on published and unpublished mitochondrial and Y-chromosomal data relative to a total of 40 populations. The results obtained reveal a striking difference in the genetic structure of farming (Bantu speakers) and hunting-gathering (Pygmies and Bushmen) populations. To explain this difference, I propose that asymmetric gene flow, polyginy and patrilocality, and hence the socio-cultural factors underlying them, have had an important role in determining and differentiating the genetic structure of sub-Saharan populations. The limits and the implications of this study are discussed.