GENETIC TRACES OF ANCIENT DEMOGRAPHY

Patterns of gene differences among humans contain information about th e demographic history of our species. Haploid loci like mitochondrial DNA and the nonrecombining part of the Y chromosome show a pattern ind icating expansion from a population of only several thousand during th e late middle or early upper Pleistocene, Nuclear short tandem repeat loci also show evidence of this expansion, Both mitochondrial DNA and the Y chromosome coalesce within the last several hundred thousand yea rs, and they cannot provide information about the population before th eir coalescence, Several nuclear loci are informative about our ancest ral population size during nearly the whole Pleistocene. They indicate a small effective size, on the order of 10,000 breeding individuals, throughout this time period, This genetic evidence denies any version of the multiregional model of modern human origins, It implies instead that our ancestors were effectively a separate species for most of th e Pleistocene.