March 21, 2012
Last week, an international group of researchers reported the discovery of fossils belonging to a strange population of hominids that lived in southwestern China as recently as 11,500 years ago, at the end of the Pleistocene Epoch. The fossils resemble modern humans in many ways but possess some unusual characteristics. The traits may be evidence that Homo sapiens were more diverse in the past—or a sign that scientists have uncovered a new species.
Anthropologist Darren Curnoe of the University of New South Wales in Australia led the analysis of the fossils, detailed in the journal PLoS ONE. The bones—a partial skull, skull cap, jaws and teeth—came from Longlin Cave in Guangxi Province and Malu Cave in Yunnan Province, and date to 11,500 to 14,300 years ago. In comparing the Chinese bones with those of recent humans, H. sapiens living during the Pleistocene, Neanderthals and Homo erectus, the researchers concluded the Chinese fossils have a unique mix of modern features and traits rarely, if ever, seen in recent and Pleistocene humans, such as a very broad face and a protruding jaw.
The most dramatic interpretation of the fossils is that they represent a newly discovered species that lived alongside modern humans in East Asia until very recently. Anthropologist Chris Stringer of the Natural History Museum in London thinks that’s a feasible idea. In fact, the fossils could be the remains of the mysterious Denisovans, Stringer told New Scientist. Scientists discovered the Denisovans a few years ago while analyzing DNA recovered from a finger bone found in a Siberian cave that dated to 30,000 to 48,oo0 years ago. The DNA didn’t align with that of modern humans or Neanderthals, the only species known to inhabit the area at the time. Since then, scientists have been looking to match a face to the DNA. This idea will be confirmed only if the researchers manage to retrieve DNA from any of the Chinese fossils.
A less headline-worthy explanation is that these hominids were members of an early, unknown migration of H. sapiens out of Africa. (Genetic evidence indicates there were at least two migrations into Eurasia: one at 60,000 to 70,000 years ago and another at 30,000 to 40,000 years ago.) Once these people settled in East Asia, they somehow remained isolated from other human populations for thousands of years and eventually died out without leaving behind descendants. Under this scenario, the population’s unusual features suggest our species was more diverse thousands of years ago than it is today. This possibility is supported by other fossils found in Africa. Curnoe and his colleagues describe H. sapiens fossils found in East, South and North Africa, dating from 12,000 to 100,000 years ago, that possess a mix of modern and more primitive traits.
This situation reminds me of the search for the earliest modern humans. Many of these fossils also retained primitive features, which has made it difficult for anthropologists to decide which ones are truly modern humans and which ones aren’t. Likewise, anthropologists now have to determine whether modern humans could have been more diverse near the end of the Pleistocene than they had previously thought or whether more hominid species were living back then than they had previously expected.
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