The aim of this lecture is to show how the study of genetic variability in human populations makes it possible to reconstruct the demographic history of our species. The study of neutral genetic diversity has highlighted several genetic characteristics of the human species : (i) reduced genetic diversity compared with the great apes, (ii) most of the genetic diversity observed in our species is due to diversity within populations themselves and not to differences between populations, and (iii) genetic distances between populations are generally proportional to geographical distances. These facts have led to the conclusion that we are a recent species, and that migration is one of the most important evolutionary forces in shaping the genetic diversity of our species.
A significant part of the lecture will be devoted to the African origins ofHomo sapiens, migration within Africa and to the rest of the globe, and the interactions between hunter-gatherers and farmers. I've also talked about how genomic studies can tell us when our species left Africa. They suggest that this dispersal, some 40 000 to 80000 years ago, was followed by a rapid colonization of southern Asia, Australia, Europe and eastern Asia. Humans even reached more distant places, the Americas, some 15 000 to 35 000 years ago, and the remote islands of Oceania, where they settled only 1 000 to 4000 years ago. The fact that population diversity decreases as one moves away from Africa is evidence of the bottlenecks and founding effects behind the continuing loss of genetic diversity as human populations migrate across the globe.
