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Global migration mapped through genetics

3 March 20141 comment

Scientists have used DNA to accurately chart the history of migration across the globe for the first time.

The ground breaking work has produced a fascinating map that shows how mixing between populations occurred.

The scientists, from University College London and the Universities of Oxford and Edinburgh, analysed modern day genomes to find pieces of DNA from common descendants.

As these pieces are passed down through generations, the size of these segments gets smaller, telling the scientists when the mixing occurred and which groups mixed; the longer the pieces of DNA, the more recent the mixing.

The study, titled ‘A Genetic Atlas of Human Admixture history’ and published in the journal Science, also focused on what happens when these separated groups come back together, known as “admixing”.

The researchers studied 95 different populations over the last 4,000 years of genetic history.

By developing sophisticated statistical methods, collectively called “Globetrotter,” the researchers were able to simultaneously identify, date and characterise genetic mixing between populations for the first time.

The research shows mixing between populations aligned with important historical events and the findings have mapped and published on  this interactive site.

“Modern genetic data combined with appropriate statistical methods have the potential to contribute substantially to our understanding of human history,” the study says.

The researchers produced an atlas of worldwide human admixture history, constructed by using genetic data alone and encompassing over 100 events occurring over the past 4,000 years.

“We identified events whose dates and participants suggest they describe genetic impacts of the Mongol empire, Arab slave trade, Bantu expansion, first millennium CE migrations in Eastern Europe, and European colonialism, as well as unrecorded events, revealing admixture to be an almost universal force shaping human populations.” The researchers said.

“Diverse historical, archaeological, anthropological, and linguistic sources of information indicate that human populations have interacted throughout history, because of the rise and fall of empires, invasions, migrations, slavery, and trade.

“These interactions can result in sudden or gradual transfers of genetic material, creating admixed populations. However, the genetic legacy of these interactions remains unknown in most cases, and the historical record is incomplete.

“Our results demonstrate that it is possible to elucidate the effect of ancient and modern migration events and to provide fine-scale details of the sources involved, the complexity of events, and the timing of mixing of groups by using genetic information alone,” the researchers said.

Some highlights of the research include:

  • The Kalash group is an isolated population in Pakistan. The Kalash show the oldest estimated date of mixing in these studies from sources that come from modern Germany and Austria. These results substantiate the belief that the Kalash originate from Alexander the Great’s invading armies.
  • In populations around the Arabian Sea, researchers detected mixing with sub-Saharan Africans from the 7th century — a period that coincided with Arab expansion and slave trade in the area.
  • The DNA of the Tu people in China points to mixing with Europeans around 1200. The source of these DNA fragments may be from merchants travelling along the Silk Road, a 4,000-mile route that facilitated trade between Europe and the Far East.
  • The expansion of the Mongol Empire was a famously rapid. These studies confirm that there was an abrupt transfer of DNA across Asia during this period. DNA evidence from the Hazara people of Pakistan agrees with historical records showing that they descended from Mongol warriors. Six other populations, from as far west as Turkey, demonstrated similar evidence of genetic mixing with Mongols around the same time.
  • South Africans who speak the Bantu languages display DNA fragments from the San people, dating back to 1222 C.E. This is consistent with the expansion of Bantu-speaking peoples from sub-Equatorial Africa into southern Africa. A second period of mixing, around 1768, shows traces of north-western European DNA, consistent with colonial-era migrants.