Science

Science

The chance discovery of two nearly intact crania, or skull caps, has given us a window into how Homo sapiens evolved in Asia over 100,000 years ago. Dubbed Xuchang 1 and 2, the crania are between 105,000 and 125,000 years old and have distinct shapes unlike anything seen before in the fossil record. Describing the new findings in Science, paleoanthropologist Xiu-Jie Wu and her colleagues say they've found an ancient human where the features are distinctly Neanderthal mixed with those of a modern human.

Zhan-Yang Li, Wu's colleague at the Institute for Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing, found miraculously undamaged fragments of the two crania in Lingjing, a village in Henan, China. A spring flowed there during the Pleistocene period when these humans would have lived, and the area was full of now-extinct megafauna like Bos (aurochs, or wild cows), Megaloceros (a massive deer), and Coelodonta (a rhino), as well as elk and horses. Bones from these animals were found with Xuchang 1 and 2, along with stone tools made from quartz. It appears that Xuchang 1 and 2 were successful hunters with a rich array of foods to eat.

They were also part of a regional group of "new or unknown archaic humans" never before seen by paleoarchaeologists in the West. Their unique "mosaic" of modern and Neanderthal traits, say Xu and colleagues in their paper, is "not known among early Late Pleistocene humans in the western Old World." It also suggests that these people came mixed with Neanderthals and other ancient populations, possibly a few times over thousands of years.

Speaking with Science News , University College London anthropologist María Martinón-Torres said one possibility is that these are the first crania discovered from Denisovans, "something with an Asian flavor but closely related to Neandertals." Denisovans are an archaic human whose DNA was sequenced based on a few finger bones and teeth. Like Xuchang 1 and 2, they combined traits of modern humans and Neanderthals.

But anthropologist Erik Trinkaus, a co-author on the new study, said he didn't want to use the term Denisovan because "it's a DNA sequence" and nothing more. Trinkaus was one of the first scientists to popularize the idea that modern humans and Neanderthals had children together. He based this hypothesis on the shape of several early human fossil skulls, and DNA analysis of modern humans eventually validated his claims. We now know that many humans alive today, especially those from Europe and Asia, have traces of Neanderthal DNA in their genomes.

What's perhaps most interesting about Xuchang 1 and 2 is their place in the grand sweep of human evolutionary history. Wu and her colleagues call them "critical" to understanding how modern humans spread throughout the Old World. They note that modern human biology was establishing itself via migrations and mixes for hundreds of thousands of years throughout many regions in Africa, the Old World, and southeast Asia. Given the nature of our evolution during the Pleistocene, it's likely that mosaic humans like Xuchang 1 and 2 might have been the rule, not the exception.

Science, 2017. DOI: 10.1126/science.aal2482

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