A 100,000 year old skull from Northern China has a structure in its inner-ear previously thought to be unique to Neanderthals. While the skull is definitely Homo Sapiens, the presence of the formation thousands of kilometers from the nearest site known to have been colonized by Homo mousteriensis suggests human evolution was more complex than we realized.

In the light of the rethinking of an earlier stage of human evolution and recent evidence on our ancestors breeding with Neanderthals it is not a total surprise to find our appearance did not run as smoothly as was once believed. Nevertheless, no one expected to find this feature so far east, nor even noticed it when the skull was first examined 35 years ago.

"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 study co-author Dr Erik Trinkaus, of Washington University, St. Louis. "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 is a long time proponent for interbreeding between Neanderthals and modern humans. He made the finding while conducting a micro-CT scan on a skull found in Xujiaya, Nihewan Basisn.

"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." 

Publishing in PNAS, Trinkaus and his coauthors say, Neanderthals “exhibit a relatively small anterior canal, a relatively larger lateral one, and a more inferior position of the posterior one relative to the lateral one.”

Three other skulls from the same region were examined for the study, two older than and one more recent than the Xujiayao 15 specimen that produced the surprise. All three resembled modern humans. The skull, and others from the same site and era, do not show any other Neanderthal features.

The researcher do not think that the find necessarily means there was some gene flow between Neanderthals living in Europe and people living in China at the time. "Eastern Asia and Western Europe are a long way apart, and these migration patterns took thousands of years to play out," says Trinkaus.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." 

The paper observes, “It raises questions regarding possible cranial and postcranial morphological correlates of Homo labyrinthine variation, the use of individual “Neandertal” features for documenting population affinities, and the nature of late archaic human variation across Eurasia.”

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