GENETIC-EVIDENCE FOR A PALEOLITHIC HUMAN-POPULATION EXPANSION IN AFRICA

Human populations have undergone dramatic expansions in size, but othe r than the growth associated with agriculture, the dates and magnitude s of those expansions have never been resolved. Here, we introduce two new statistical tests for population expansion, which use variation a t a number of unlinked genetic markers to study the demographic histor ies of natural populations, By analyzing genetic variation in various aboriginal populations from throughout the world, rye show highly sign ificant evidence for a major human population expansion in Africa, but no evidence of expansion outside of Africa. The inferred African expa nsion is estimated to have occurred between 49,000 and 640,000 years a go, certainly before the Neolithic expansions, and probably before the splitting of African and non-African populations. In showing a signif icant difference between African and non-African populations, our anal ysis supports the unique role of Africa in human evolutionary history, as has been suggested by most other genetic work. In addition, the mi ssing signal in non-African populations may be the result of a populat ion bottleneck associated with the emergence of these populations from Africa, as postulated in the ''Out of Africa'' model of modern human origins.