NewMexiKen spent this afternoon reading Steve Olson’s Mapping Human History: Discovering the Past through Our Genes (2002). The book is informative and interesting, though it gives the vague impression of articles strung together. Some items of interest:
Every single one of the 6 billion people on the planet today is descended from the small group of anatomically modern humans who once lived in eastern Africa. The group occasionally came close to extinction, but it never died out completely, and eventually it began to expand. By about 100,000 years ago, modern humans had moved north along the Nile Valley and across the Sinai Peninsula into the Middle East. More than 60,000 years ago they made their way along the coastlines of India and southeastern Asia and sailed to Australia. About 40,000 years ago, modern humans moved from northeastern Africa into Europe and from southeastern Asia into eastern Asia. Finally, sometime more than 10,000 years ago, they made their way along a wide plain joining Siberia and Alaska and spread down the length of North and South America. (Page 3)
In comparing the DNA sequences of people from many locations around the world, geneticists have been able to measure the genetic differences between individuals and between groups. What they have found is that about 85 percent of the total amount of genetic variation in humans occurs within groups and only 15 percent between groups. In other words, most genetic variants occur in all human populations. Geneticists have to look hard to find variants concentrated in specific groups.
The pattern is quite different in other large mammals. Among elephants of eastern and southern Africa, 40 percent of the total genetic differences occurs between groups. For the gray wolves of North America, group differences account for 75 percent of the total genetic variation. Most conservation biologists hold that group genetic differences have to exceed 25 to 30 percent for a single species to divided into subspecies or races. By this measure, human races do not exist. (Page 63)