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More evidence for Neanderthal-human mixing claimed

Oct. 30, 2006
By Neil Schoenherr/Washington University in St. Louis 
and World Science staff

A new study claims to help set­tle a decade-old con­tro­ver­sy over wheth­er our an­ces­tors in­t­er­bred with Ne­an­der­thals, find­ing that they prob­a­bly did. But some sci­ent­ists say a con­clu­sive an­s­wer may have to await a re­cons­truction of the Ne­an­der­thal ge­nome, due to be fi­nished soon.

Er­ik Trinkaus of Wash­ing­ton Uni­ver­si­ty in St. Lou­is, Mo., and col­leagues an­a­lyzed se­v­er­al ear­ly mo­d­ern hu­man bones from a cave in Ro­ma­nia known as Pes­te­ra Mu­i­e­rii, or Cave of the Old Wo­m­an.

Top: a bro­ken cra­ni­um from the Pes­te­ra Mu­e­ie­rii ca­ve in Ro­ma­nia. The scale at left marks cent­i­me­ters. (Cour­te­sy PNAS).

The bones turned up in 1952 but have been large­ly ig­nored by sci­ence be­cause of ear­ly dif­fi­cul­ties in dat­ing them ac­cu­rate­ly, ac­cord­ing to Trin­kaus. 

He con­tends that the new stu­dy, us­ing mo­d­ern dat­ing tech­niques, helps piece to­geth­er the here­to­fore fuz­zy pic­ture of the fate of the stock­y, hea­vy-browed folk known as Ne­an­der­thals. 

They vanished near­ly 30,000 years ago from their Eu­ro­pe­an haunts, ten or twen­ty thou­sand years af­ter an­a­to­m­i­cal­ly mo­d­ern hu­mans ap­peared on the con­ti­nent.

Con­t­ro­versy has cen­tered on wheth­er mod­ern hu­mans wiped them out, ab­sorbed them in­to their pop­u­la­tion, or a lit­tle of both.

The Ro­ma­nian fos­sils be­tray “con­si­der­able” in­t­er­breed­ing, wrote Trin­kaus and col­leagues in this week’s ear­ly on­line edi­tion of the re­search jour­nal Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ces.

Draw­ings of a Ne­an­derthal (top left) and mod­ern hu­man (bot­tom right) cra­ni­um.

“These ear­li­est mod­ern hu­mans had a mo­sa­ic of dis­tinct­ly mod­ern hu­man char­ac­ter­is­tics and oth­er char­ac­ter­is­tics which align them with Ne­an­der­thals, sug­gest­ing some com­bi­na­tion of mod­ern hu­mans dis­pers­ing in­to Eu­rope and in­ter­act­ing with and ab­sorb­ing the Ne­an­der­thal pop­u­la­tion,” Trin­k­aus said.

The researchers said they dat­ed the fos­sils to 30,000 years ago. The bones—added to a small num­ber of sim­i­lar­ly old re­mains of mod­ern hu­mans known from var­i­ous sites in Eu­rope—help fill out a pre­vi­ously un­clear pic­ture of of ear­ly mod­ern hu­man anat­o­my, they added.

The fos­sils show mod­ern hu­man fea­tures such as nar­row nose and small up­per jaw­bone, front teeth and brow ridge, Trin­kaus and col­leagues said. But these co-exist with prim­i­tive, Ne­an­der­thal-associated fea­tures, they added, in­clud­ing a shoul­der bone some­what awk­ward­ly adapted for spear-throwing.

Past stud­ies, though, have shown con­flict­ing re­sults on the ques­tion of Ne­an­der­thal mix­ture with mod­ern hu­mans. Re­search pub­lished in last Ju­ly’s is­sue of the re­search jour­nal PLoS Ge­net­ics found that mod­ern Eu­ro­pe­ans are at least 5 per­cent Ne­an­der­thal. But a study us­ing dif­fer­ent meth­ods that ap­peared in the De­cem­ber 2004 is­sue of PLoS Bi­ol­o­gy, a re­lat­ed jour­nal, con­clud­ed that genes re­veal ev­i­dence for lit­tle or no in­ter­breed­ing.

The earlier of these studies com­pared mo­dern hu­man DNA to a spe­ci­fic type of Ne­an­der­thal DNA found in fos­sils. The la­ter stu­dy ex­p­loi­ted the fact that if two po­pu­la­tions with dif­fer­ent fre­quen­cies of cer­tain genes mix, their des­cen­dants will have some com­bi­na­tions of those genes more or less often than the un­mixed po­pu­la­tions.

There are some possible rea­sons for the dis­c­re­pan­cies in the findings, Vin­cent Plag­nol of the Uni­ver­si­ty of South­ern Cal­i­for­nia, au­thor of the lat­er stu­dy, wrote in an e­mail. A fi­nal an­s­wer, he ad­ded, may not come until re­search­ers com­p­lete a re­con­struc­tion of the Ne­an­der­thal ge­nome; that proj­ect is in the works and should be done “any­time now.”

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New evidence helps settle a decade-old controversy over whether humans and Neandertals mated, concluding that they probably did, some researchers claim. Erik Trinkaus of Washington University in St. Louis, Mo., and colleagues analyzed several early modern human bones from a cave known as Pestera Muierii, or Cave of the Old Woman, in Romania. The bones turned up in 1952 but have been largely ignored by science because of difficulties in dating them with certainty, according to Trinkaus. He contends that the new study, using reliable dating techniques, helps piece together the heretofore fuzzy picture of what happened to the stocky, heavy-browed human relatives known as Neanderthals. They disappeared nearly 30,000 years ago from their European haunts, ten or twenty thousand years after anatomically modern humans appeared on the same continent. Controversy has centered on whether modern humans wiped them out, absorbed them into their population, or a little of both. The Romanian fossils have a blend of Neanderthal and early modern human properties, Trinkaus said. “These earliest modern humans had a mosaic of distinctly modern human characteristics and other characteristics which align them with Neandertals, suggesting some combination of modern humans dispersing into Europe and interacting with and absorbing the Neandertal population,” he said. Writing in this week’s early online edition of the research journal pnas, Trinkaus and colleagues said they directly dated the fossils to 30,000 years ago. The bones, added to a small number of similarly old remains of modern humans from various sites in Europe, help fill out a previously unclear picture of of early modern human anatomy, the researchers added. The fossils show modern human features such as narrow nose, a small small upper jawbone and front teeth and small brow ridge, Trinkaus and colleagues said. But these co-exist with primitive, Neanderthal-associated features, they added, including a shoulder bone somewhat awkwardly adapted for spear-throwing. Past studies, though, have shown conflicting results on the question of Neanderthal mixture with modern humans. A study published in last July’s issue of the research journal PLoS Genetics found that modern Europeans are at least 5% Neanderthal. But a study using different methods that appeared in the December 2004 issue of PLoS Biology, a related journal, concluded that modern genes reveal evidence for little or no interbreeding.