Point­ing to a new di­rec­tion

A fin­ger bone from an un­ex­pected place and time up­ends the story of hu­man mi­gra­tion out of Africa.

The Star Malaysia - Star2 - - Science - By KAREN KA­PLAN

IT’S only three cen­time­ters long and less than one cen­time­ter wide, but it has the po­ten­tial to re­write the his­tory of our an­ces­tors’ mi­gra­tion out of Africa.

The ob­ject in ques­tion is a fos­silized piece of a bone, prob­a­bly the mid­dle por­tion of a mid­dle fin­ger. Based on its shape, sci­en­tists be­lieve that it be­longed to a mem­ber of the Homo sapi­ens species.

Two things make it un­usu­ally sig­nif­i­cant. First, ura­nium se­ries dat­ing tech­niques in­di­cate that the bone is be­tween 85,000 and 90,000 years old.

Sec­ond, it was found in Al Wusta, a site in Saudi Ara­bia’s Ne­fud desert that’s hun­dreds of miles from the near­est coast­line.

Those fac­tors stand in sharp con­trast to the tra­di­tional “out of Africa” nar­ra­tive of hu­man mi­gra­tion. Based on both ar­chaeo-

log­i­cal ev­i­dence and ge­netic anal­y­sis, this the­ory posits that mod­ern hu­mans left their home con­ti­nent about 60,000 years ago and stayed near the coasts as they spread out across the world.

But re­cent dis­cov­er­ies have poked holes in this story.

Sci­en­tists have found what ap­pear to be Homo sapi­ens teeth in Chi­nese caves that sug­gest hu­mans ar­rived there much ear­lier. In the Fuyan Cave, for in­stance, teeth were found among min­eral de­posits that were at least 80,000 years old. In the Luna Cave, more teeth were un­cov­ered among ma­te­rial that is be­lieved to be be­tween 130,000 and 70,000 years old.

In Aus­tralia, ar­chae­ol­o­gists turned up 65,000-year-old stone tools and other ar­ti­facts that sug­gest hu­mans had reached the north­ern part of the con­ti­nent by then.

The fin­ger bone from Al Wusta, how­ever, marks the first time sci­en­tists have tested the age of a hu­man fos­sil from so far be­yond Africa and found it to be sig­nif­i­cantly older than 60,000 years, ac­cord­ing to a re­port on the work in the jour­nal Na­ture Ecol­ogy & Evo­lu­tion.

“This dis­cov­ery of the fos­sil fin­ger bone, for me, is like a dream come true,” said ar­chae­ol­o­gist Michael Pe­traglia, the se­nior au­thor of the study. “It has ma­jor im­pli­ca­tions with re­spect to how our species came out of Africa and the route and the path­ways that they took out of Africa.”

The bone it­self was found pok­ing out of the sur­face of the Al Wusta ex­ca­va­tion site in 2016 by Iyad Zal­mout, a pa­le­on­tol­o­gist with the Saudi Ge­o­log­i­cal Sur­vey.

“He picked up the bone,” Pe­traglia re­called, “and he im­me­di­ately recog­nised it as hu­man. It was that dis­tinc­tive.”

To be ab­so­lutely sure, mem­bers of the study team put the fos­sil in a CT scan­ner and took pre­cise mea­sure­ments of its shape. Then they com­pared that shape with dozens of fin­ger bones from hu­mans, non-hu­man pri­mates and ex­tinct ho­minin species.

Al­though the fos­sil “falls within the range of vari­a­tion” of go­ril­las, Old World mon­keys, Ne­an­derthals,

Aus­tralo­p­ithe­cus afaren­sis and A. sed­iba, all of its shape ra­tios are “most sim­i­lar” to the fin­ger bones of Homo sapi­ens, ac­cord­ing to the study.

(In­ci­den­tally, the CT scan re­vealed a small lump on the bone that could have been caused by the stress of pro­duc­ing stone tools, said Pe­traglia, who holds po­si­tions at Ger­many’s Max Planck In­sti­tute for the Sci­ence of Hu­man His­tory and at the Smith­so­nian In­sti­tu­tion’s Na­tional Mu­seum of Nat­u­ral His­tory in Wash­ing­ton.)

Us­ing lasers, re­searchers col­lected a mi­cro­scop­i­cally small sam­ple of the fos­silised bone and used it to gauge its age. The anal­y­sis showed that that bone was about 87,600 years old, give or take 2,500 years.

The fin­ger bone wasn’t the only find at the site.

Team mem­bers also un­earthed hun­dreds of an­i­mal fos­sils, in­clud­ing hip­popota­muses, an­te­lope and ex­tinct species of African wild cat­tle.

“These an­i­mals tell us that when hu­mans were liv­ing there, it was not a desert,” said first au­thor Huw Grou­cutt, an ar­chae­ol­o­gist at the Univer­sity of Ox­ford. In­stead, mon­soon rains had trans­formed the area into a grass­land with fresh­wa­ter lakes and rivers. “There were abun­dant an­i­mals and a lot of peo­ple liv­ing there,” Grou­cutt said.

In fact, lush pe­ri­ods like this one might have turned the Ara­bian Penin­sula into “a sort of stag­ing post that sucks peo­ple in and them pumps them out” to spread fur­ther east into Eura­sia, he added.

The find­ings demon­strate that cli­mate change aided the spread of our species ear­lier than pre­vi­ously thought. When the Saudi fin­ger bone is com­bined with the teeth from China and the ar­ti­facts from Aus­tralia, “it does all fit to­gether very neatly”, Grou­cutt said.

It’s a con­vinc­ing story that changes our view of Homo sapi­ens’ emer­gence from Africa, ac­cord­ing to Univer­sity of Tulsa an­thro­pol­o­gist Don­ald Henry, who was not in­volved in the new work.

When sea lev­els were lower than they are to­day, our an­ces­tors could have crossed from Africa to the south­ern tip of the Ara­bian Penin­sula via the Bab el Man­deb strait, Henry said.

To­day, this is where the Red Sea meets the Gulf of Aden. But 90,000 years ago, there would have been a large river and an ex­ten­sive fer­tile area that wel­comed plants, an­i­mals and even hu­mans.

“Trac­ing the evo­lu­tion and geo­graphic dis­per­sal of the hu­man lin­eage is rather like con­nect­ing piti­fully few dots on a vast three-di­men­sional grid of time and space,” Henry wrote in an es­say that ac­com­pa­nies the study.

The fos­silised fin­ger bone rep­re­sents “a very sig­nif­i­cant dot that pro­vides a new ref­er­ence point for hu­man dis­per­sal”. – Los An­ge­les Times/Tri­bune News Ser­vice

A gen­eral view of the ex­ca­va­tions at the Al Wusta site in Saudi Ara­bia. The an­cient lake bed, in white, is now sur­rounded by sand dunes of the Ne­fud Desert. — Pho­tos: TNS

Four views of the fos­sil fin­ger bone. Sci­en­tists say it be­longed to a mem­ber of the Homo sapi­ens species who lived about 88,000 years ago. The bone it­self is about 3cm long and less than 1cm across.

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