Neandertals Not Our Ancestors, DNA Study Suggests (Whewww!!!)

One more piece of evidence has been added to the debate on whether there was any interbreeding between Neandertals and early modern humans.

Around 50,000 years ago, small groups of anatomically modern humans migrated out of Africa and began to colonize the rest of the world. Known as Cro-Magnons for the site in France where the earliest remains were found, these early humans co-existed with the Neandertals then living in Europe until the Neandertals became extinct roughly 30,000 years ago. What happened and why—did the two groups war, did they mate, did they even meet?—has been an enduring puzzle in the study of human origins.

A team of geneticists from Italy and Spain compared the mitochondrial DNA (mtDNA) of two Cro-Magnons that were 23,000 and 25,000 years old respectively, four Neandertal specimens, 29,000 to 42,000 years old, and a large database of modern human mtDNA to shed some light on the issue.

The authors found that the Cro-Magnon mtDNA fit well within the spectrum of genetic variation exhibited by modern Europeans, but differed sharply from that of the Neandertals. They conclude that it is unlikely that Neandertals contributed to the current European gene pool.

"Our results add to the evidence collected previously in different fields, making the hypothesis of a 'Neandertal heritage' very unlikely," said Giorgio Bertorelle, a geneticist at University di Ferrara in Italy, and a co-author of the study.

The results were published in the May 12-16 issue of the Proceedings of the National Academy of Sciences.

Understanding Early Human Origins

The research was designed to address a question raised by two different theories on human evolution. The replacement model holds that a wave of anatomically modern humans left Africa around 50,000 years ago, and eventually replaced the existing Neandertal populations.

Advocates of the multi-regional theory argue that there was gene flow between the two populations and that modern humans have dual ancestry: archaic and modern.

"These results match with views, including mine, that the Neandertals were largely or totally replaced rather than absorbed into the Cro-Magnon gene pool, but the samples are small and it is possible that other samples or other genes might tell a different story," said Chris Stringer, director of the Human Origins program at the Natural History Museum in London.

Mitochondrial DNA is passed solely through the mother.

"We can say pretty absolutely that Neandertals didn't contribute mitochondrial DNA to modern humans, but that's just one locus and doesn't carry very strong implications for the rest of the genome," said Henry Harpending, an anthropologist at the University of Utah. "I'm not saying they did interbreed, it's just that mtDNA is a restricted data set."

Typically, if there is interbreeding between two groups of unequal status, it often occurs between the males of the more developed culture and the females of the less developed culture.

"An article was recently published speculating that the selective advantage that modern humans had was reproductive; that the development of a broader pelvis and wider birth canal to accommodate bigger skulls and larger brains made the difference," said Harpending. "If that were the case, it would be easy to imagine that Neandertal women breeding with anatomically modern men would have had a real hard time, and mtDNA might not show up in the modern human genome."

Multi-regional proponents say the lack of similar mtDNA between Neandertals and Cro-Magnons doesn't answer the question of interbreeding.

"What multi-regionalists have been saying all along is that it's about mixture and evolution; that there was gene flow and that Neandertals are one of the ancestors of modern humans," said Milford Wolpoff, a paleontologist at the University of Michigan. "What these data show is that people who lived 20,000 years ago look [genetically] more like people today than the people who lived 45,000 years ago."

"It seems to me that's proving the obvious. It's not telling us that much about the progress in evolution," he said. "You would expect Neandertals to look more and more like modern humans as time goes on."

Looking to the Future

The analysis of ancient nuclear DNA is not technically feasible at the moment, and probably won't be anytime in the near future, the researchers say. But advances in the field of genetics and the mapping of the human genome has provided a flood of information that may someday yield the answers.

"What we need now is to find our way through the databases," said Harpending. "None of the models we have now can explain all of the evidence."

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