A Harvard study casts new light on the intermingling and migration of European, Middle Eastern and African and populations since ancient times.
     While previous studies have established that such shared ancestry exists, they have not indicated to what degree or how far back the mixing of populations can be traced.
     "The genetic decay happens very slowly," doctoral student Priya Moorjani explains, "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 average - 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.
     The dates of population mixtures are consistent with documented historical events - the mixing of African and southern European populations with events during the Roman Empire and Arab migrations that followed, and dates among African and Jewish populations with events in biblical times.
     Reich concludes that his lab's findings have significant cultural and genetic implications. "Population boundaries that many people think are impermeable are, in fact, not that way."

Edited from EurekAlert! (24 May 2011), PLoS Genetics (April 2011)