“Genes Tell New Story on the Spread of Man,” Science/Health, The New York Timeson the Web, December 7, 1999 by Nicholas Wade:
“Two genetic surveys of human populations bring new evidence to bear on a pivotal event in prehistory, the first dispersal of modern humans from Africa. One study, based on analysis of people in East Africa and India, suggests that the first emigration of modern humans was eastward, toward Asia, and not northward through the eastern Meditrranean.
“A second, drawing on DNA data from 50 ethnic groups around the world, concludes that the ancestral population from which the first emigrants came may have numbered as few as 2,000 people.
“Both studies suggest that the most recent common ancestor of the emigrants lived 60,000 to 40,000 years ago.
“Previous genetic studies have suggested 100,000 years or so for the most recent common ancestor, and about 10,000 for the ancestral population size. The younger date of about 50,000 years seems to tally much better with an emerging synthesis of the archaeological data relating to human origins.
“ ‘A combination of fossil and genetic evidence locates the ancestral population in Africa,and archaeological discoveries imply an initial dispersal out of Africa about 50,000 years ago.’ Dr. Richard Klein of Stanford University writes in the latest edition of his book ‘The Human Career.’
“ … Dr. Klein and others believe that some major genetically based neurological change, like the development of language occurred about 50,000 years ago. This transformation, he infers, was the spur that led behaviorally modern humans to innovate their characteristic suite of more advanced stone implements, develop the first form of art and spread throughout the world.
“The remains of modern humans dating to about 100,000 years ago have been found at a well-known archaeological site called Skhul in Israel. The finding has been interpreted as evidence of the first human migration out of Africa, and it fit with the old genetic data of a modern human origin.
“ … The study, published in Nature Genetics last week, is based on mitochondrial DNA, the genetic material of the small energy producing organelles inside every cell. Because mitochondria are inherited with the egg, from the mother alone, their DNA escapes the shuffling that occurs in sexual reproduction, and any changes reflect the occasional random mutation in the DNA. On the basis of these mutations, biologists can construct a family tree of mitochondrial lineages and, by estimating the mutation rate, figure out the time that has elapsed since the mutation at the root of the tree.
East Africa was the homeland origin of people in India and discoveries made in 2000 provided the first genetic evidence indicating that the human migration route out of Africa was from eastern Africa along the coast toward Southeast Asia and Australia 60,000 to 40,000 years ago:
“ … Dr. Santachiara-Benerecetti and her colleagues studied a particular pattern of mitochondrial DNA that is well known in India. They found an earlier form of the pattern among people in Ethiopia, suggesting that East Africa was its place of origin. Signs of the pattern also exist among many people in Saudi Arabia, but not among inhabitants of the eastern Mediterranean. This provides the first genetic evidence, the Italian biologists say, that the human migration route out of Africa was from eastern Africa along the coast toward Southeast Asia and Australia.
“Another new genetic study, by Dr. Marcus Feldman of Stanford University and others, makes an interesting counterpart to the Italian study because it is based on a different kind of DNA but reaches similar conclusions. Dr. Feldman and his colleagues looked at segments of the Y chromosome, another part of the human genome that escapes the usual shuffling of the reproductive process. Studying Y chromosomes from around the world, they concluded that the most recent common ancestor of all these Y’s was carried by a man who lived only 40,000 years or so ago. Even though all Y chromosomes can be traced back to a single individual, this does not mean a single Adam was the species’ only male representative. The founding population from which the world’s present population is deerived consisted of about 2,000 individuals, according to the new data, Dr. Feldman said. One Y chromosome in such a population will eventually dominate in the descendants after all the other Y lineages are brough to a half, whether because their owners have no children or beget only daughters. The 40,000-year date,which has a large range of uncertainty, is much more recent than others, in part because the earlier estimates were forced to assume, quite unrealistically, that the size of the human population remained constant throughout prehistory. …”