Study: Human DNA Neanderthal-Free
Posted: Monday, May 12, 2003
By Jennifer Viegas, Discovery News
May 12, 2003 — Neanderthals did not contribute to the gene pool of modern humans, according to a recent study that compared the DNA of two ancient Cro-Magnons with that of four Neanderthals.
While Neanderthals and early humans coexisted in Europe for a few thousand years 40,000 years ago, the findings suggest they did not interbreed, an action that would have made Neanderthals a direct ancestor of modern humans.
The study also supports the "Out of Africa" theory. According to this view, modern humans evolved in East Africa and then spread into Europe and Asia through the Middle East.
This opposes the "multiregional mode of expansion" theory, which holds that early humans, including Neanderthals, were unique but related populations within one evolving species.
For the study, published in the current Proceedings of the National Academy of Sciences, researchers extracted mitochondrial DNA from Cro-Magnon skeletons found in the Paglicci cave of Southern Italy. The first set of remains dated to approximately 23,000 years ago. The second individual lived around 24,720 years ago.
Mitochondrial DNA is inherited unchanged from the mother only, allowing researchers to trace unadulterated DNA back hundreds of thousands of years.
When the Cro-Magnon mtDNA was compared with existing mtDNA data from four Neanderthals dating between 29,000-42,000 years ago, virtually no similarities were found.
The genetic information then was compared with that of four prehistoric Europeans who lived between 5,500-14,000 years ago, and also with a database of mtDNA information for 2,566 modern Europeans and Near Easterners.
No matches were found when Neanderthals were compared with ancient and modern humans. Cro-Magnons, however, had genetic sequences present in 14 percent of the modern humans represented in the database, particularly individuals from the Near and Middle East.
"In samples from Yemen, Syria, Iran, Palestine are found individuals with a sequence belonging to the same group as the Paglicci samples," explained Giorgio Bertorelle, an author of the PNAS paper and an assistant professor of population genetics and genetic epidemiology at the University of Ferrara in Italy.
The link to the Near and Middle Eastern countries seems reasonable, Bertorelle said, because this was the likely route of expansion that early humans followed.
Alan Cooper, professor of zoology at Oxford University, agreed with the findings, but suggests that Neanderthals should not be ruled out just yet as direct human ancestors.
"There is still a remote possibility that only nuclear DNA was contributed, or that any Neanderthal mtDNA lineage has been lost during human population bottlenecks in the last glacial max, but the odds appear pretty slim," said Cooper.
Henry Harpending, professor of anthropology at the University of Utah, also hesitated to rule out the possibility of a human-Neanderthal connection. Harpending further believes that the multiregional mode of expansion theory still is plausible, as "mtDNA seems to have a different history than much of the rest of the genome."
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