Friday, January 13, 2006

Ashkenazi Jews Can Trace Their Genes to Four Ancient Women

Brian
Last month's year-end Economist explored the evolution of the human race and cited the identification of a source mother for living humans:
Whichever way you drew the tree (statistics not being an exact science, there was more than one solution), its root was in Africa. Homo sapiens was thus unveiled as an African species. But Dr Cann went further. Using estimates of how often mutations appear in mitochondrial DNA (the so-called molecular clock), she and Wilson did some matridendrochronology. The result suggests that all the lines converge on the ovaries of a single woman who lived some 150,000 years ago.

There was much excited reporting at the time about the discovery and dating of this African “Eve”. She was not, to be clear, the first female Homo sapiens. Fossil evidence suggests the species is at least 200,000 years old, and may be older than that. And you can now do a similar trick for the patriline using part of the male (Y) chromosome in the cell nucleus, because this passes only from father to son. Unfortunately for romantics, the most recent common ancestor of the Y-chromosome is a lot more recent than its mitochondrial equivalent. African Adam was born 60,000-90,000 years ago, and so could not have met African Eve. Nevertheless, these two pieces of DNA as they have weaved their ways down the generations have filled in, in surprising detail, the highways and byways of human migration across the face of the planet.
Link. The issue also discussed some of the recent genetic evidence linking intelligence, neurological disorders, and Ashkenazi Jews:
Until a century or two ago, the Ashkenazim—the Jews of Europe—were often restricted by local laws to professions such as banking, which happened to require high intelligence. This is the sort of culturally created pressure that might drive one of Dr Deacon's feedback loops for mental abilities (though it must be said that Dr Deacon himself is sceptical about this example). Dr Cochran, however, suspects that this is exactly what happened. He thinks the changes in the brain brought about by the genes in question will be shown to enhance intelligence when only one copy of a given disease gene is present (you generally need two copies, one from each parent, to suffer the adverse symptoms). Indeed, in the case of Gaucher's disease, which is not necessarily lethal, there is evidence that sufferers are more intelligent than average. If Ashkenazi Jews need to be more intelligent than others, such genes will spread, even if they sometimes cause disease.
Link. Now even more recent research finds the Ashkenazim's own Eve, or rather Eves:
Some 3.5 million of today's Ashkenazi Jews—about 40 percent of the total Ashkenazi population—are descended from just four women, a genetic study indicates.

Those women apparently lived somewhere in Europe within the last 2,000 years, but not necessarily in the same place or even the same century, said lead author Dr. Doron Behar of the Rambam Medical Center in Haifa, Israel.

He did the work with Karl Skorecki of the Technion-Israel Institute of Technology and others.

Each woman left a genetic signature that shows up in their descendants today, he and colleagues say in a report published online by the American Journal of Human Genetics. Together, their four signatures appear in about 40 percent of Ashkenazi Jews, while being virtually absent in non-Jews and found only rarely in Jews of non-Ashkenazi origin, the researchers said.
Link. When you think of all our genetic commonalities, and how all these people you hang out with, work with, and date are essentially your own not-so-distant cousins, doesn't it make you feel like a Jeff Foxworthy joke waiting to happen?

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