Wednesday, June 20, 2018

Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past II

Later chapters discuss the state of affairs of ancient genomic studies in regions other than Europe. The Indus Valley received migrations of farmers from Iran 9000 years ago, and they spread south into the heart of India by about 5000 years ago. 3000 to 4000 years ago, India split into two main population groups with one in the north and one in the south. The northern group was strongly affected by descendants of the same Yamnaya group that had entered Europe, and these genes show up conspicuously in the caste system, with the Brahmins exhibiting the most European genes. The genes correspond with the spread of Indo-European languages in the region. There are parallels between the Rig Veda, composed over 3000 years ago, and the slightly more recent Iliad and Odyssey. Across India, the caste system has created many different genetic bottlenecks related to inbreeding, which have caused an increased frequency in several diseases. These bottlenecks have effects not unlike those seen in Finns and Ashkenazi Jews. In the Americas, Native Americans are hampering progress in research because they believe that it violates their cultural traditions, even when ancient remains are not those of their ancestors. Research is now underway in China, where the Han constitute a majority. In China and elsewhere, "ghost populations," i.e. large ancient groups that have no archaeological identification, have been found. Tibetans appear to be related to Asian hunter-gatherers and Han Chinese.  Africa is one of the least studied regions in DNA research. This is partly the result of the deterioration of human DNA in tropical environments. Europe is currently the location of the most intensive DNA research, because that is where most of the technology has developed.

I found one chapter, "The Genomics of Inequality," somewhat disappointing. Reich discusses the inherent biological advantage that men have in spreading their genes, in that women can have only a few children whereas men can have many. For example, Genghis Khan, the founder of the Mongol Empire who died in 1227, is thought to have millions of living descendants who are identified by a unique feature of his Y chromosome. Reich, oddly I think, describes the historical events associated with high levels of male reproduction as inequality. For example, a study has shown that, among African Americans, the men have 38 percent European ancestry while the women have 10 percent: These numbers imply that the contribution of European American men to the genetic makeup of the present-day African American population is about four times that of European American women. In other words, many male slave owners, like Thomas Jefferson, were having children with their slaves, and their wives were not. A similar pattern is evident in ancient DNA studies of the Yamnaya. It is true that an inherent social inequality is present when men are free to have as much sex as they like with women from lower social strata, but Reich seems to go out of his way to frame the phenomenon in politically correct terms when, from a scientific standpoint, it could just as well be described as natural selection at work. Whether you like it or not, natural selection is a numbers game, and nature doesn't care whether a larger population comes into being as a result of equality or inequality. For that matter, all species eventually become extinct – what's fair about that? I'm cutting Reich a little slack, because he walks a thin line in which his lab at Harvard could be bombed if he inadvertently offended someone.

This book is a short summary of research in what is rapidly growing into an enormous field. Some aspects of the research are simply interesting in themselves as new tools for exploring human history. There are also more practical aspects, such as the understanding of the genetics behind certain diseases. The field will eventually provide a much clearer picture of the role of mutations in our evolution. Above all, since this is a scientific enterprise, I am hopeful that it will someday put to rest much of the mythological nonsense that underlies the thinking in all societies and makes the world a far more dangerous place than it needs to be. When you frame human history in millenia rather than in decades or centuries, ethnicity and race become ephemera, as does the claim to ownership of land.

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