for National Geographic News
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 whydid 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.