Genetics and the Search for Modern Human Origins

Abstract

Genetics and the Search for Modern Human Origins John H. Relethford Wiley-Liss, New York, 2001 ISBN 0-471-38413-5 The author, a population geneticist on the faculty of the State University of New York at Oneonta, has written a well-organized and most readable book which investigates what for well over a century has been one of the most hotly contested subjects in academe. As is well known, the study of anatomical traits early established the evolution of man from primate origins. By the middle of the twentieth century, what is today known as the Multi-Regional Theory of the origin of living humans was generally accepted. I choose to speak of "living humans" rather than of "modern humans" in this context, since the latter expression is poorly defined and is capable of many differing interpretations. Although the term "modern humans" is widely used by contemporary academic writers, there is a great deal of confusion as to when modern humans first appeared. This is because evolution is essentially a chicken-and-egg process; it is hardly possible to discover an anatomically modern child that was sired by parents who could be defined as non-modern. Even living human populations vary in so many details that it has been pointed out that virtually all the individual anatomical features which, taken as a whole, distinguish Classic Neanderthals can be found amongst one or other of the living varieties of man. Only when aggregated together in a single skeleton do they unequivocally mark that fossil to be Neanderthal. Implicitly acknowledging this problem, the author does not attempt to determine any set of traits that define either modern humans or Neanderthals but instead explains that the common approach is to take as many traits as possible to minimize statistical error and evolutionary fluctuations and get an estimate of the average degree of dissimilarity between the two arbitrarily chosen groups selected for the study. The radical essence of the Out of Africa theory, based on genetic and anatomical data of both fossils and living populations, argues that the ancestors of all living humans reached "modernity" in Africa, and that small populations moved out of Africa into Eurasia as recently as circa 120,000 years ago. Although there is massive evidence that other hominitis were already present in Eurasia at that time, the strict Out of Africa theory maintains that these "modern human" migrants totally replaced their non-modern predecessors in Eurasia instead of mixing their genes with them because of either mutual infertility or a primordial racist refusal on the migrants' part to interbreed with the "inferior" native stocks whom they supplanted. However, a few anatomists have persisted in pointing to the seemingly incontrovertible evidence of regional anatomical continuity from pre-modern into modern populations in certain parts of Eurasia, claiming that the human populations currently living outside Africa must have inherited at least some of their genes from earlier pre-modern populations of that area, if indeed they had not evolved quite independently from earlier non-African populations. The evidence advanced to support this view of Multi-Regional Evolution is strongest amongst the Mongoloids of Eastern Asia. During the last century, debate also centered on the theory that the Classic Neanderthals who occupied Western Eurasia down to around 40,000 years ago had evolved into modern Europeans or, more likely, had at least contributed some genes to the incoming, fully modern Cro-Magnon populations that supplanted them. Both views have now been rejected because of convincing DNA evidence acquired from Neanderthal fossils. This actually has less similarity to the DNA of modern European populations than with hat of contemporary East Asian, African and Australoid populations, although Neanderthal DNA is essentially dissimilar from that of all living humans. Similarly mitochrondrial DNA recovered from the remains of European Neanderthals does not show any reasonable degree of similarity to the mtDNA of contemporary modern Europeans, which is not surprising in light of the vast anatomical differences which separate them from the Cro-Magnon ancestors of living European Caucasoids. …