by DANIEL COSSINS
The Kalash people who live in the Hindu Kush Mountains of modern Pakistan carry genes that probably originated in Europe and might have been carried East by the Macedonian Army of Alexander the Great. PHOTO/James L. Stanfield/National Geographic Creative
Encounters among populations left marks in the DNA of living people.
The study, published today in Science1, uses statistical methods to make inferences about which populations interbred, and when, over the past 4,000 years. The findings are also presented as an interactive map. The authors sequenced DNA from 1,490 people from 95 genetically distinct populations around the world, and tested almost 500,000 single-letter variations in DNA known as single nucleotide polymorphisms, or SNPs.
Eighty of the populations showed evidence of genetic mixing. Many of the mixing events identified are consistent with historical records, validating the approach. For instance, records suggest that the Hazara people of Afghanistan and Pakistan are descended partially from Mongol warriors, and the study confirmed this, showing that Mongol DNA entered the Hazara around the time that the Mongol Empire was expanding.
Other mixing events inferred by the study were previously unknown and do not show up in historical records, but may be plausible. For instance, sequences in the DNA of the Tu people from modern China indicate that Europeans similar to modern Greeks mixed with an East Asian population around 1200 bc. The source of this European DNA might have been merchants travelling the Silk Road.
In another example, the DNA of the Kalash people, a population isolated in a remote valley in Pakistan, showed evidence of input from Europe or the Middle East (the researchers could not pin down a precise geographic location) between 990 and 210 bc — a period that overlaps with that of Alexander the Great. Local Kalash tradition holds that they are descended from Alexander the Great’s army, although there is no historical record of such a mixture.
Nature for more