An­cient DNA shows ear­li­est Amer­i­cans came from Asia

The News & Observer (Sunday) - - News - BY CARL ZIM­MER

Nearly 11,000 years ago, a man died in what is now Ne­vada. Wrapped in a rab­bit-skin blan­ket and reed mats, he was buried in a place called Spirit Cave.

Now sci­en­tists have re­cov­ered and an­a­lyzed his DNA, along with that of 70 other an­cient peo­ple whose re­mains were dis­cov­ered through­out the Amer­i­cas. The find­ings lend as­ton­ish­ing de­tail to a story once lost to pre­his­tory: how and when hu­mans spread across the Western Hemi­sphere.

The ear­li­est known ar­rivals from Asia were al­ready split­ting into rec­og­niz­ably dis­tinct groups, the re­search sug­gests. Some of these pop­u­la­tions thrived, be­com­ing the an­ces­tors of indige­nous peo­ples through­out the hemi­sphere.

But other groups died out en­tirely, leav­ing no trace save for what can be dis­cerned in an­cient DNA. In­deed, the new ge­netic re­search hints at many dra­matic chap­ters in the peo­pling of the Amer­i­cas that ar­chae­ol­ogy has yet to un­cover.

“Now, this is the grist for ar­chae­ol­o­gists,” said Ben Pot­ter of the Univer­sity of Alaska, who was not in­volved in the new pa­pers. “Holy cow, this is awe­some.”

Ear­lier stud­ies had in­di­cated that peo­ple moved into the Amer­i­cas at the end of the last ice age, trav­el­ing from Siberia to Alaska across a land bridge now un­der the Ber­ing Sea. They spread south­ward, even­tu­ally reach­ing the tip of South Amer­ica.

Un­til re­cently, ge­neti­cists could of­fer lit­tle in­sight into these vast mi­gra­tions. Five years ago, just one an­cient hu­man genome had been re­cov­ered in the Western Hemi­sphere: that of a 4,000-year-old man dis­cov­ered in Green­land.

The lat­est batch of analy­ses, pub­lished in three sep­a­rate stud­ies this week, marks a turn­around. In the past few years, re­searchers have re­cov­ered the genomes of 229 an­cient peo­ple from teeth and bones dis­cov­ered through­out the Amer­i­cas.

One of them is a rare in­di­vid­ual, only the sec­ond so-called An­cient Beringian whose DNA has ever been an­a­lyzed.

The first, de­scribed in Jan­uary by Eske Willer­slev, a ge­neti­cist at the Univer­sity of Copen­hagen, was a 11,500-year-old girl whose re­mains were found in east­ern Alaska.

The sec­ond was dis­cov­ered hun­dreds of miles away, in western Alaska, and lived 9,000 years ago, Willer­slev and his col­leagues re­ported Thurs­day in the jour­nal Science.

The An­cient Beringians sep­a­rated from the an­ces­tors of liv­ing indige­nous peo­ple in the Amer­i­cas about 20,000 years ago. The new find­ings sug­gest they en­dured for sev­eral thou­sand years. Then they dis­ap­peared, leav­ing no known ge­netic trace in liv­ing peo­ple.

But an­other wave of mi­grants from Siberia did not stop in Alaska. They kept mov­ing, even­tu­ally ar­riv­ing south of the ice age glaciers. Then they split into two branches.

One group turned and headed north, fol­low­ing the re­treat­ing glaciers into Canada and back to Alaska. The other branch took a re­mark­able jour­ney south.

The ge­netic data sug­gest that this group spread swiftly across much of North Amer­ica and South Amer­ica about 14,000 years ago. The ex­pan­sion may have taken only cen­turies.

“It’s ba­si­cally an ex­plo­sion,” Willer­slev said.

The man from Spirit Cave in Ne­vada be­longed to this south­ern branch of mi­grants. He also was closely re­lated to a 12,700year-old boy found on the other side of the Rocky Moun­tains in Mon­tana, Willer­slev also found.

But the man from Spirit Cave also turned out to have a close ge­netic link to 10,400-year-old skele­tons found in Brazil, on the other side of the equa­tor.

David Re­ich of Har­vard Univer­sity and his col­leagues found a sim­i­lar pat­tern in their own re­search, pub­lished Thurs­day in the jour­nal Cell.

They un­cov­ered a link be­tween the an­cient Mon­tana boy and an­other group of an­cient South Amer­i­cans, in­clud­ing a 10,900-year-old skele­ton in Chile. Like Willer­slev’s work, the kin­ship sug­gests that mi­grants moved quickly from North Amer­ica to South Amer­ica.

“We agree that this must be a rapid ra­di­a­tion,” Re­ich said.

Start­ing about 9,000 years ago, both teams found, ad­di­tional waves of peo­ple moved south­ward. Willer­slev’s re­search sug­gests the new ar­rivals mixed with older South Amer­i­can pop­u­la­tions.

Re­ich, on the other hand, sees ev­i­dence for two waves of mi­grants who com­pletely re­placed the peo­ple who had lived in South Amer­ica.

The new re­search also re­vealed in­stances of re­mark­able con­ti­nu­ity, kin­ships that spanned thou­sands of years.

Willer­slev and his col­leagues com­pared the genome of the man from Spirit Cave to those of four sets of re­mains found nearby in Ne­vada’s Love­lock Cave, who lived as re­cently as 600 years ago.

All of these peo­ple were closely re­lated, his team found, de­spite be­ing sep­a­rated by 10,000 years of his­tory.

In 2015, Re­ich and his col­leagues found that some liv­ing peo­ple in the Ama­zon carry some DNA that’s most sim­i­lar to that of peo­ple who live to­day in Aus­tralia and New Guinea.

The re­searchers spec­u­lated that their ances­try in­cluded an un­known group, which the sci­en­tists called Pop­u­la­tion Y, who sep­a­rately made their way into the Amer­i­cas.

In their new study, Re­ich and his col­leagues found no trace of Pop­u­la­tion Y – but Willer­slev’s team suc­ceeded in iden­ti­fy­ing their DNA in some of the 10,400-year-old skele­tons in Brazil.

“The mil­lion-dol­lar ques­tion ob­vi­ously is, how did this hap­pen?” Willer­slev said.

Per­haps an­other group of Asians en­tered the Amer­i­cas long be­fore the an­ces­tors of the man from Spirit Cave and other early Na­tive Amer­i­cans. Maybe they in­ter­bred with peo­ple in the Ama­zon be­fore dis­ap­pear­ing al­to­gether.

Or per­haps a few of the early mem­bers of the south­ern branch hap­pened to have some odd genes that sur­vived through the gen­er­a­tions.

The new rush of ge­netic sam­ples re­flects an im­prov­ing work­ing re­la­tion­ship be­tween sci­en­tists and indige­nous peo­ples. For decades, many tribes re­jected re­quests for DNA from re­searchers.

The man from Spirit Cave, for ex­am­ple, was dug up by ar­chae­ol­o­gists in 1940 and stored in a mu­seum. The lo­cal tribe, the Fal­lon Paiute-Shoshone, didn’t learn of the body till 1996.

LI­NUS MØRK, MA­GUS FILM NYT

Eske Willer­slev, cen­ter, talks to mem­bers of the Fal­lon Paiute-Shoshone tribe in Ne­vada. With per­mis­sion from the tribe, Willer­slev was able to re­trieve DNA from a tooth be­long­ing to the Spirit Cave man.

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