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Inner Ear Fossil Shakes Up The Understanding Of Human Evolution

July 8, 2014
Image Caption: The Xujiayao 15 late archaic human temporal bone from northern China, with the extracted temporal labyrinth, is superimposed on a view of the Xujiayao site. Credit: Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Science

Brett Smith for redOrbit.com – Your Universe Online

Originally thought to be a sequential progression, human evolution has been shown to include a rich tapestry of species that interbred over thousands of years.

A new study from Washington University in St. Louis has revealed yet another twist in this intricate story of our evolution. Based on the re-examination of an approximately 100,000-year-old early human skull found in Northern China, the new study discovered an inner-ear structure previously thought to be exclusive to Neanderthals.

“The discovery places into question a whole suite of scenarios of later Pleistocene human population dispersals and interconnections based on tracing isolated anatomical or genetic features in fragmentary fossils,” said Erik Trinkaus, a physical anthropology professor at WUStL and co-author of the new study, which will be published in the Proceedings of the National Academy of Sciences.

“It suggests, instead, that the later phases of human evolution were more of a labyrinth of biology and peoples than simple lines on maps would suggest,” Trinkaus added.

The study team used micro-CT scans to reveal the interior configuration of a temporal bone within the ancient skull, which was part of a collection of skulls found at the Chinese site during the 1970s that all seemed to have characteristics typical of an early non-Neanderthal form of human.

“We were completely surprised,” Trinkaus said. “We fully expected the scan to reveal a temporal labyrinth that looked much like a modern human one, but what we saw was clearly typical of a Neanderthal. This discovery places into question whether this arrangement of the semicircular canals is truly unique to the Neanderthals.”

Frequently still intact in mammal skulls, the semicircular canals at the center of the study are remains of a liquid-packed sensing system that helps humans maintain balance when they switch their spatial orientations, such as when jogging, bending over or rotating the head from side-to-side.

Since the mid-1990s, the presence of an explicit formation of the semicircular canals in the temporal labyrinth was enough to consider fossilized skull fragments as being from a Neanderthal. This structure was also used as a marker to set Neanderthals apart from both earlier and modern humans.

Trinkus said the new find supplements numerous theories that attempt to explain human origins, movement patterns and possible interbreedings. The study team cautioned against drawing the conclusion that Neanderthal interbreeding could be the cause for finding this structure in a skull thought to be from a different species.

“The study of human evolution has always been messy, and these findings just make it all the messier,” Trinkaus said. “It shows that human populations in the real world don’t act in nice simple patterns.”

“Eastern Asia and Western Europe are a long way apart, and these migration patterns took thousands of years to play out,” he added. “This study shows that you can’t rely on one anatomical feature or one piece of DNA as the basis for sweeping assumptions about the migrations of hominid species from one place to another.”

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Source: Brett Smith for redOrbit.com - Your Universe Online



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