At­las of hu­man ge­netic his­tory

The Star Malaysia - Star2 - - SCIENCE -

SCI­EN­TISTS have mapped the ef­fects of war, coloni­sa­tion, trade, mi­gra­tion and slav­ery on the ge­netic mix­ing of hu­mans over the bulk of recorded his­tory and cre­ated an on­line in­ter­ac­tive at­las of hu­man­ity’s ge­netic his­tory.

In a paper pub­lished last week in the jour­nal Sci­ence, re­searchers de­tailed the ge­netic mix­ing be­tween 95 pop­u­la­tions across Europe, Africa, Asia and South Amer­ica dur­ing 100 his­tor­i­cal events over the last 4,000 years.

The events cov­ered in the in­ter­ac­tive at­las in­clude the ex­pan­sion of the Mon­gol em­pire by Genghis Khan, the Arab slave trade, the so-called Bantu ex­pan­sion into South­ern Africa, and Euro­pean colo­nial­ism.

When people from dif­fer­ent groups in­ter­breed, their off­spring’s DNA be­comes a mix­ture of both ad­mix­ing groups. Sci­en­tists say pieces of this DNA are passed down to fol­low­ing gen­er­a­tions, al­though the size of the seg­ments be­come smaller and smaller.

By study­ing the size of the DNA seg­ments in present-day hu­mans, re­searchers can in­fer how long ago it was that the ad­mix­ture oc­curred.

“Each pop­u­la­tion has a par­tic­u­lar ge­netic ‘pal­ette’,” said study co-au­thor Daniel Falush, an evo­lu­tion­ary ge­neti­cist at the Max Planck In­sti­tute for Evo­lu­tion­ary An­thro­pol­ogy in Leipzig, Ger­many.

“Though we can’t di­rectly sam­ple DNA from the groups that mixed in the past, we can cap­ture much of the DNA of these orig­i­nal groups as per­sist­ing within a mixed pal­ette of mod­ern-day groups,” he said in a pre­pared state­ment.

To ac­com­plish this, re­searchers used a so­phis­ti­cated sta­tis­ti­cal method called “Glo­be­trot­ter” to an­a­lyse genome data from 1,490 in­di­vid­u­als.

While ge­netic sig­nals ob­tained from a sin­gle in­di­vid­ual might be rel­a­tively weak, they strengthen as sci­en­tists look at a larger group. As a re­sult, re­searchers found that their ge­netic data matched his­tor­i­cal events and pe­ri­ods.

One such ex­am­ple in­volved the legacy of the Mon­gol em­pire, re­searchers said. Traces of Mon­gol DNA in the Hazara peo- ple of Pak­istan sup­port his­tor­i­cal ac­counts that the Hazara de­scended from Mon­gol war­riors.

In pop­u­la­tions sur­round­ing the Ara­bian Sea, re­searchers de­tected mix­ing with sub-Sa­ha­ran Africans be­tween AD 890 and 1754. That pe­riod seemed to co­in­cide with Arab ex­pan­sion and slave trade, the au­thors said.

In other cases, the re­searchers found mix­ing that es­caped the no­tice of his­to­ri­ans.

“The DNA of the Tu people in mod­ern China sug­gests that in around (AD) 1200, Euro­peans sim­i­lar to mod­ern Greeks mixed with an other­wise Chi­nese-like pop­u­la­tion,” said co-au­thor Si­mon My­ers, a bioin­for­mat­ics and sta­tis­tics ex­pert at Ox­ford Univer­sity.

“Plau­si­bly, the source of this Euro­pean-like DNA might be mer­chants trav­el­ling the nearby Silk Road,” he said.

Of the 95 pop­u­la­tions stud­ied, 80 showed ev­i­dence of ad­mix­ture, while nine groups could not be char­ac­terised by the sta­tis­ti­cal method, re­searchers said. – Los Angeles Times / McClatchyTri­bune In­for­ma­tion Ser­vices

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