Heredity 2008 100 555 563 2008 Nature Publishing Group All rights reserved 0018 067X 08 30 00 SHORT REVIEW www nature com hdy Genetic evidence and the modern human origins debate JH Relethford Department of Anthropology State University of New York College at Oneonta Oneonta NY USA A continued debate in anthropology concerns the evolutionary origin of anatomically modern humans Homo sapiens sapiens Different models have been proposed to examine the related questions of 1 where and when anatomically modern humans first appeared and 2 the genetic and evolutionary relationship between modern humans and earlier human populations Genetic data have been increasingly used to address these questions Genetic data on living human populations have been used to reconstruct the evolutionary history of the human species by considering how global patterns of human variation could be produced given different evolutionary scenarios Of particular interest are gene trees that reconstruct the time and place of the most recent common ancestor of humanity for a given haplotype and the analysis of regional differences in genetic diversity Ancient DNA has also allowed a direct assessment of genetic variation in European Neandertals Together with the fossil record genetic data provide insight into the origin of modern humans The evidence points to an African origin of modern humans dating back to 200 000 years followed by later expansions of moderns out of Africa across the Old World What is less clear is what happened when these early modern humans met preexisting archaic human populations outside of Africa At present it is difficult to distinguish between a model of total genetic replacement and a model that includes some degree of genetic mixture Heredity 2008 100 555 563 doi 10 1038 hdy 2008 14 published online 5 March 2008 Keywords modern human origins population genetics paleoanthropology Introduction These and other questions fall under what has been termed the modern human origins debate Although this debate is often focused on the fossil and archeological records studies of genetic variation have become increasingly important as a source of insight Much of the work in this area has consisted of detailed analyses of patterns of genetic variation in living human populations The strategy here is based on the realization that whatever our species evolutionary past it has left visible signatures on our genome Expectations of current genetic variation under different evolutionary scenarios are compared with observed genetic variation in our species in order to test various origin models In addition the last decade has also seen an increase in the analysis of ancient DNA such that mitochondrial and nuclear DNA sequences are now available for the Neandertals an archaic human group The purpose of this review is to highlight some of the major findings of genetic analysis using both living and ancient DNA and their use and misuse in the modern human origins debate The focus here is primarily on recent findings and the status of the debate as I perceive it A long standing debate in anthropology concerns our own origins as anatomically modern humans Homo sapiens sapiens The qualifying term anatomically modern is used to identify our early ancestors that were physically much the same as living humans but also to distinguish them from earlier hominins that could be called human at some level based on features such as an increased brain size relative to body size and the possession of a material culture including stone tools The fossil record of the past 2 Myr shows modern humans evolving from earlier humans often referred to as archaic humans a broad group that includes the species H heidelbergensis as well as the Neandertals of Europe and the Middle East What is less clear is the evolutionary relationship of modern humans to the various archaic human populations as well as to earlier ancestors Did modern humans evolve via anagenesis from a single archaic species across the Old World or did they first arise in Africa If the latter then did modern populations expanding out of Africa replace the archaic human populations that lived outside of Africa or did they interbreed with them Were the Neandertals a separate species from modern humans and if so did any hybridization take place The fossil record of evolution in the genus Homo Correspondence Dr JH Relethford Department of Anthropology State University of New York College at Oneonta Fitzelle Hall 311 Oneonta NY 13820 USA E mail relethjh oneonta edu Received 5 September 2007 revised 25 January 2008 accepted 1 February 2008 published online 5 March 2008 In order to understand the contributions of genetic research to the modern human origins debate it is first necessary to provide a brief review of the fossil record for human evolution over the past 2 Myr Only a brief review is given here more detail is available in many current texts on human evolution e g Conroy 2005 Stringer Genetics and modern human origins JH Relethford 556 and Andrews 2005 Molecular evidence suggests that the hominin and African ape lines diverged about 6 7 Myr ago The fossil record of the first possible bipeds dates back over 6 Myr ago in Africa By 4 2 Myr ago there is definite evidence of bipedal hominins in Africa Australopithecus anamensis These early hominins walked upright at least on the ground had ape sized brains and larger protruding faces and teeth The species H erectus appeared in Africa 1 8 Myr ago and is characterized by modern limb proportions increased brain size reduction in the size of the teeth and developments in stone tool technology Until this point in time hominin evolution had taken place exclusively in Africa but populations of H erectus dispersed to Eastern Europe and Southeast Asia about 1 7 Myr ago note some anthropologists refer to the initial African population as the species H ergaster and reserve the name H erectus for the Southeast Asian populations Some populations of Southeast Asian H erectus may have survived until 27 000 54 000 years ago and perhaps are related to the newly named dwarf species H floresiensis although others consider the type specimen to be a pathological modern human The descendants of H ergaster H erectus have often been referred to broadly as archaic humans a label that bridges the gap between early humans H ergaster H erectus and modern humans H sapiens sapiens The archaic humans have on average a brain size approaching that of
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