Ancient DNA and the origin of modern humans.

Abstract

Central to the debate over the origin of modern Homo sapiens are arguments over the mode, location, and timing of the transition from large-brained “archaic humans” to anatomically modern human form. Some argue for an African replacement model, where modern Homo sapiens arose as a new species in Africa roughly 150–200 thousand years ago (ka), followed by their dispersal throughout the Old World replacing archaic human groups (including the Neandertals). Others argue for a multiregional interpretation, where the transition from archaic to modern humans took place within a single evolutionary lineage extending back as far as 2 million years ago (1, 2). Some variants of multiregional evolution suggest that the transition to modernity first occurred in Africa and was then shared across the Old World through gene flow, while others argue that modern traits appeared in different times and places, such that modern humans evolved through the coalescence of these changes (3). The basic difference between African replacement and multiregional evolution advocates is between those favoring speciation and replacement and those favoring evolution within a single species. The debate over modern human origins has been addressed using the fossil and archaeological records, as well as reconstructions of evolutionary history based on the examination of patterns of genetic diversity within and between populations of living humans. In 1997, the genetic evidence was extended to prehistoric samples with the successful extraction of a mitochondrial DNA (mtDNA) sequence from the European Neandertal specimen from Feldhofer Cave in Germany (4). Since then, Neandertal mtDNA has also been extracted from Neandertal specimens from Mezmaiskaya Cave in the northern Caucasus (5) and from Vindija Cave, Croatia (6). These studies noted the difference between the mtDNA of Neandertals and living humans, and they suggested that these differences reflect separate species status for the Neandertals, implying an …