A closer look at a 100,000-year-old human skull that was recovered 35 years ago in China revealed that it had an inner ear formation that was thought only to have occurred in Neanderthals.
It was long thought that only the Neanderthals, who lived in western Asia and Europe from between 30,000 years to 40,000 years ago, had such inner ear characteristics before the discovery. The findings on the skull, codenamed Xujiayao 15, showed that the characteristics were more geographically widespread.
The report on the discovery was published in the Proceedings of the National Academy of Sciences journal.
Erik Trinkaus, PhD, co-author of the report and a Washington University of St. Louis physical anthropology professor, said that the discovery suggests a complicated "labyrinth" of people and biology for the later stages of human evolution, as opposed to simple lines that connect the evolution phases from one to another.
The discovery was made when micro-CT scans on a fossilized human skull, excavated in the 1970s in the Xujiayao site in the Nihewan Basin in China, revealed a temporal bone that had a configuration similar to Neanderthals, when the team that did the micro-CT scan expected the configuration to look more like that of a modern human's.
The semicircular canals in the ear are often well-preserved inside the fossils of mammal skulls. The canals used to be filled with fluid, working as a system that helps humans keep their balance when moving spatially. Early research on CT scans confirmed the existence of the canals in the mid-1990s, with a particular arrangement of the canals since being considered enough to identify if a skull is a Neanderthal.
However, Xujiayao 15 was found with other human bone and teeth fossils that are characterized as early form of late archaic humans that were not Neanderthal.
"The study of human evolution has always been messy, and these findings just make it all the messier," said Trinkaus. "It shows that human populations in the real world don't act in nice simple patterns."
Theories that attempt to explain the discovery include interbreeding between the Neanderthals and the Chinese late archaic humans. However, with the massive distance of time and location between the two human species, the migration patterns that led to the development may have taken thousands of years to come into place.
The co-authors of Tinkaus in the report are Wu Liu, Xiu-Jie Wu, and Song Xing from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and Isabelle Crevecoeur of PACEA, Université de Bordeaux in France.
