PubMed1984
A central problem of human evolution is whether the transition from Homo erectus to Homo sapiens was anagenetic or cladogenetic. The existence of H. erectus at Zhoukoudian between 460,000 and 230,000 years B.P. is consistent with early cladogenesis or a later transition. Evidence from mitochondrial DNA suggests present day humans could have evolved from a population existing between 180,000 and 360,000 years ago. Genetic distance studies based on nuclear genes suggest divergence between Negroids and Mongoloid-Caucasoids 115,000 years ago and between Caucasoids and Mongoloids 41,000 years ago. Recent fossil evidence is consistent with these estimates. Other evidence is accumulating that Asia is the heartland for the emergence of Homo sapiens. The earliest clearly defined North American culture (Clovis) was established at most by 14,000 years B.P. and on some views had spread to Tierra del Fuego by 11,000 B.P. Other evidence from geographically diverse areas suggests an earlier arrival. The initial human occupation of the Americas probably occurred somewhere between 12,000 and 40,000 years ago. However, much of the work on dating skeletal material has yielded inconsistent or unreliable information. Paleoecology indicates that at the maximum lowering of sea-level, 18,000 years ago, the Beringia land bridge was 1000 Km wide and was an inhospitable region of wind-blown dunes and discontinuous vegetation. However, there may have been patches of greater productivity. One theory suggests humans were widely distributed in Beringia as early as 35,000 B.P. and had penetrated Alaska and Yukon by 25,000 B.P. Again, however, the archaeological evidence for early occupation is conflicting and uncertain. Evidence based on analysis of gene frequencies and on dental data suggests North American origins by 19,000 and 15,000 respectively. Further, both the genetic and dental evidence favour an Asian origin, but whether the result of a single or multiple migrations is still an open question. The view here is that the erectus-sapiens transition took place somewhere in South Asia between 125,000 to 200,000 years ago, with the appearance of anatomically modern man by 30-40,000 B.P. Sometime between 30,000-15,000 B.P. the first people crossed Beringia to North America, spreading to occupy all of the Americas rapidly. The ancestors of the Na-Dene Indians and the Aleut-Eskimos were later and perhaps separate arrivals from Asia between 14,000-8,500 B.P. The Eskimo ancestors arose finally by a fissioning of the Aleutian Island-Southwest Alaskan maritime population about 4,000 years ago.