According to the biological species concept, two varieties of anything are considered one species if they can interbreed and produce fertile offspring.  Applied to humans, new evidence suggests that Neanderthals and the recently-discovered Denisovans (12/29/2010) were members of the human species.    According to New Scientist, “On the western fringes of Siberia, the Stone Age Denisova cave has surrendered precious treasure: a toe bone that could shed light on early humans’ promiscuous relations with their hominin cousins.”  Since one can only be promiscuous within the same species, this puts enormous pressure on evolutionary timelines that assume the Denisovans split from the Neanderthals 300,000 years ago.

New Scientist said the toe bone found in the Siberian cave of Denisova, announced by Svante Paabo (Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany), looks like something between that of a Neanderthal and a modern human.  Reporter Colin Barras speculated that Paabo’s team has DNA evidence that will be announced in a forthcoming publication suggesting the toe came from a Neanderthal-Denisovan hybrid.  “If so,” Barras concluded, “there may be a case for reclassifying all three as members of the same species.”

In Nature News, Ewen Callaway reported more about ancient DNA from archaic humans.  Callaway tantalized, “scientists are racing to apply the work to answer questions about human evolution and history that would have been unfathomable just a few years ago.”  Recent work has shown that living non-African people share 4% of their genes with Neanderthals, clearly indicating inter-species breeding.  Yet the ancestry of Neanderthals and modern humans were thought to be separated by 200,000 years of evolution.  In addition, “The denizens of Denisova also bred with contemporary humans” whose DNA can be traced to modern Melanesians, “thousands of miles away from Denisova, suggesting that the Denisovans had once lived across Asia.”  Given the propensity of modern humans for travel and technology, it seems a stretch that these members of a common species could have remained separated for tens of thousands of years….

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