"The genetic decay happens very slowly," Moorjani explained, "so today, thousands of years later, there is enough evidence for us to estimate the date of population mixture."
While the researchers detected no African genetic signatures in Northern European populations, they found a distinct presence of African ancestry in Southern European, Middle Eastern and Jewish populations. Modern southern European groups can attribute about 1 to 3 percent of their genetic signature to African ancestry, with the intermingling of populations dating back 55 generations, on averagethat is, to roughly 1,600 years ago. Middle Eastern groups have inherited about 4 to 15 percent, with the mixing of populations dating back roughly 32 generations. A diverse array of Jewish populations can date their Sub-Saharan African ancestry back roughly 72 generations, on average, accounting for 3 to 5 percent of their genetic makeup today.
According to Reich, these findings address a long-standing debate over African multicultural influences in Europe. The dates of population mixtures are consistent with documented historical events. For example, the mixing of African and southern European populations coincides with events during the Roman Empire and Arab migrations that followed. The older-mixture dates among African and Jewish populations are consistent with events in biblical times, such as the Jewish diaspora that occurred in 8th to 6th century BC.
"Our study doesn't prove that the African ancestry is associated with migrations associated with events in the Bible documented by archeologists," Reich says, "but it's interesting to speculate."
Reich was surprised to see any level of shared ancestry between the Ashkenazi and non-Ashkenazi Jewish groups. "I've never been convinced they were actually related to each other," Reich says, but he now concludes that his lab's findings have significant cultu
|Contact: David Cameron|
Harvard Medical School