Resumo de The Journey Of Man: A Genetic Odyssey

In The Journey of Man: A Genetic Odyssey (2002), Spencer Wells uses maps, diagrams, and Mark Read?s color photographs to supplement his account of the prehistoric spread of human beings from eastern Africa to almost every place on earth except Antarctica. Although he often refers to mtDNA (mitochondrial deoxyribonucleic acid), passed only from mother to child, he concentrates on Y chromosomes, passed only from father to son, because their changes of form give a clearer picture of where genetically modern humans were, when they were there, how they got there, and how closely they are related to others of their species.As for his debts, Wells accepts the contemporary paleoanthropological idea of an African origin of human beings, and he relies both on a genetic application of William of Ockham?s principle of parsimony and on the recent work of the linguist Joseph Greenberg and such geneticists as Luca Cavalli-Sforza. As for his beginning arguments, Wells claims that all women today can trace their mtDNA to one African woman who lived about 150,000 years ago and that all men today can trace their Y chromosomes to one African Man who lived about 59,000 years ago, a time of fast technological advance in comparison to what had come before. The great genetic diversity among humans in Africa, says Wells, supports the idea of an African origin for all modern humans, and genetic evidence further shows that Neanderthals are not the ancestors of anyone alive now.The first migration of genetically modern humans from Africa started near the Red Sea about 50,000 years ago with a man who bore the Y-chromosomal marker called M168. From him descended a man who bore the M130 marker. Following the coast of the Indian Ocean, the descendants of the M130 man eventually reached Australia, although the rise in sea level after the end of the last ice age makes archaeological evidence of their trip of many generations hard to find. Furthermore, other M130 men traveled slowly up the eastern coast of Asia and eventually reached Alaska and places much farther south along North America?s western coast. About 45,000 years ago, coming from a bearer of M168 but not M130, appeared the M89 marker, common in men of western Asia and northeastern Africa. Next, about 40,000 years before the present, a man with an M89 marker fathered a boy with an M9 marker, and the latter?s descendants over the years moved deeper into Eurasia. In turn, about 35,000 years before now, a man with an M175 marker came from a man with an M9 marker, and the M175 males moved toward southeastern Asia. About the same time, someone with an M45 marker was born to a man with an M9 marker, and the M45 males migrated north into central Asia. Then, about 30,000 years ago, from an M45 came a male with an M173 marker, whose descendants gradually moved as far as westernmost Europe. Also about 30,000 years ago, an M20 line derived from the M9 line, with the M20?s journeying south into India. In another 10,000 years, in central Asia, bearers of the M242 marker came from a bearer of the M45 marker and made their way into Siberia. Finally, in Wells?s account, four genetic events of great note occurred with the Y chromosome about 10,000 years ago, during the Neolithic Age. From a bearer of M242 came bearers of M3, who ventured through Alaska into the rest of North America and down to the southern tip of South America. From the M89 line in western Asia came a line, M172, which entered southeastern Europe through Asia Minor. From M173?s came M17?s, the Indo-Europeans, who populated the Eurasian steppes and even crossed the mountain barrier to enter India. And from M175 came M122, a chromosomal line common in eastern Asia. Thus, according to Wells, all persons now alive are related, more closely than many of us would have thought, and the lineage of modern humanity is much shorter than that of hominids as a whole. As the development of agriculture influenced human movement and therefore human genetic geography, so has the development of industry and the increased mobility it has effected. Contemporary mixing of peoples leads not only to less linguistic diversity but also to genetic patterns that are becoming less geographically distinct.

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