Tracing Ancestry, Researchers Produce a Genetic Atlas of Human Mixing Events - NYTimes.com - 0 views
www.nytimes.com/...as-of-human-mixing-events.html
history methods technology ancestry human mixing genome
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geneticists applying new statistical approaches have taken a first shot at both identifying and dating the major population mixture events of the last 4,000 years, with the goal of providing a new source of information for historians.
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Some of the hundred or so major mixing events they describe have plausible historical explanations, while many others remain to be accounted for.
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many populations of the southern Mediterranean and Middle East have segments of African origin in their genomes that were inserted at times between A.D. 650 and 1900, according to the geneticists’ calculations. This could reflect the activity of the Arab slave trade,
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The lowest amount of African admixture occurs in the Druse, a religious group of the Middle East that prohibited slavery and has been closed to converts since A.D. 1043.
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Another mixing event is the injection of European-type DNA into the Kalash, a people of Pakistan, at some time between 990 and 210 B.C. This could reflect the invasion of India by Alexander the Great in 326 B.C. The Kalash claim to be descended from Alexander’s soldiers
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Though all humans have the same set of genes, their genomes are studded with mutations, which are differences in the sequence of DNA units in the genome. These mutations occur in patterns because whole sets of mutations are passed down from parent to child and hence will be common in a particular population
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The dating system is based on measuring the length of chromosome segments of a particular ancestry that occur in a population. When people of two different populations intermarry, their children’s genomes carry large chunks of DNA of one parent’s ancestry interspersed with large chunks from the other’s.
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from the average size of the chunks in a person’s genome, the geneticists can calculate the number of generations since the mixing event.
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One of the most widespread events his group has detected is the injection of Mongol ancestry into populations within the Mongol empire, such as the Hazara of Afghanistan and the Uighur Turks of Central Asia.
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the European colonization of America is recorded in the genomes of the Maya and Pima Indians. And Cambodian genomes mark the fall of the Khmer empire in the form of ancestral DNA from the invading Tai people.
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They find among Northern Italians an insertion of Middle Eastern DNA that occurred between 776 B.C. and A.D. 550, and may represent the Etruscans, a mysterious people said by the ancient Greek historian Herodotus to have emigrated from Lydia in Turkey.
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his method cannot yet detect genetic mixing between very similar populations, as was the case with the English and their invaders from Scandinavia and Northern Germany.
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“In some sense we don’t want to talk to historians,” Dr. Falush said. “There’s a great virtue in being objective: You put the data in and get the history out. We do think this is a way of reconstructing history by just using DNA.”