Study finds why Jewish mothers are so important
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Four Jewish mothers who lived 1,000 years ago in Europe are the ancestors of 40 percent of all Ashkenazi Jews alive today, an international team of researchers reported on Friday.
The genetic study of DNA paints a vivid picture of human evolution and survival, and correlates with the well-established written and oral histories of Jewish migrations, said Dr. Doron Behar of the Technion-Israel Institute of Technology, who worked on the study.
The study, published in the American Journal of Human Genetics, suggests that some 3.5 million Jews alive today all descended from four women.
For their study, Behar and geneticist Karl Skorecki, with collaborators in Finland, France, Estonia, Finland, Portugal, Russia and the United States sampled DNA from 11,452 people from 67 populations.
“All subjects reported the birthplace of their mothers, grandmothers, and, in most cases, great-grandmothers,” they note in their report.
They looked at mitochondrial DNA, which is found in cells, outside the nucleus and away from the DNA that carries most genetic instructions. Mitochondrial DNA is passed down virtually unchanged from mother to daughter, but it does occasionally mutate, at a known rate.
Researchers can use this molecular clock to track genetic changes through time, and used it, for instance, to compute when the “ancestral Eve” of all living humans lived—in Africa, about 180,000 years ago.
Now they have found four ancestral Jewish mothers.
“I think there was some kind of genetic pool that was in the Near East,” Behar said in a telephone interview.
“Among this genetic pool there were four maternal lineages, four real women, that carried the exact specific mitochondrial DNA markers that we can find in mitochondrial DNA today.”
SETTLING EUROPE
They, or their direct descendants, moved into Europe.
“Then at a certain period, most probably in the 13th century, simply by demographic matters, they started to expand dramatically,” Behar said.
“Maybe it was because of Jewish tradition, the structure of the family that might have been characterized by a high number of children.”
But these four families gave rise to much of the population of European Jews—which exploded from 30,000 people in the 13th century to “something like 9 million just prior to World War II,” Behar said.
The Nazis and their allies killed 6 million Jews during the war, but there are now an estimated 8 million Ashkenazi Jews, defined by their common northern and central European ancestry, cultural traditions and Yiddish language.
Behar said as they sampled people from Ashkenazi communities around the world, the same mitochondrial genetic markers kept popping up. They did not find the markers in most of the non-Jewish people they sampled, and only a very few were shared with Jews of other origin.
This particular study does not provide a direct explanation for some of the inherited diseases that disproportionately affect Jews of European descent, such as breast and colon cancer, because most diseases are caused by mutations in nuclear DNA, not the DNA studied by Behar’s group.
These genes are believed to date from a “bottleneck” phenomenon, when populations were squeezed down from large to small and then expanded again. Behar and Skorecki’s team have found what is known as a “founder effect”—when one or a small number of people have a huge number of descendants.
What the study also shows, Behar said, is that Jewish mothers are highly valued for a good reason. “This I could tell you even without the paper,” he said.
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