A view of modern human origins from Y chromosome microsatellite variation

The idea that ail modern humans share a recent (within the last 150,000 yea rs) African origin has been proposed and supported on the basis of three ob servations. Most genetic loci examined to date have (I) shown greater diver sity in African populations than in others, (2) placed the first branch bet ween African and all non-African populations in phylogenetic trees, and (3) indicated recent dates for either the molecular coalescence (with the exce ption of some autosomal and X-chromosomal loci) or for the time of separati on between African and non-African populations. We analyze variation at 10 Y chromosome microsatellite loci that were typed in 506 males representing 49 populations and every inhabited continent and find significantly greater Y chromosome diversity in Africa than elsewhere, find the first branch in phylogenetic trees of the continental populations to fail between African a nd all non-African populations, and date this branching with the (delta mu) (2) distance measure to 5800-17,400 or 12,800-36,800 years BP depending on the mutation rate used. The magnitude of the excess Y chromosome diversity in African populations appears to result from a greater antiquity of Africa n populations rather than a greater long-term effective population size. Th ese observations are most consistent with a recent African origin for all m odern humans.