Re-examination of a circa 100,000-year-old archaic early human skull found 35 years ago in Northern China has revealed the surprising presence of an inner-ear formation long thought to occur only in Neandertals.
“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 Erik Trinkaus, PhD, a physical anthropology professor at Washington University in 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.”
The study, forthcoming in the Proceedings of the National Academy of Sciences, is based on recent micro-CT scans revealing the interior configuration of a temporal bone in a fossilized human skull found during 1970s excavations at the Xujiayao site in China’s Nihewan Basin.
Trinkaus, the Mary Tileston Hemenway Professor in Arts & Sciences, is a leading authority on early human evolution and among the first to offer compelling evidence for interbreeding and gene transfer between Neandertals and modern human ancestors.
His co-authors on this study are Xiu-Jie Wu, Wu Liu and Song Xing of the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, and Isabelle Crevecoeur of PACEA, Université de Bordeaux.
“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 Neandertal. This discovery places into question whether this arrangement of the semicircular canals is truly unique to the Neandertals.”
Often well-preserved in mammal skull fossils, the semicircular canals are remnants of a fluid-filled sensing system that helps humans maintain balance when they change their spatial orientations, such as when running, bending over or turning the head from side-to-side.
Since the mid-1990s, when early CT-scan research confirmed its existence, the presence of a particular arrangement of the semicircular canals in the temporal labyrinth has been considered enough to securely identify fossilized skull fragments as being from a Neandertal. This pattern is present in almost all of the known Neandertal labyrinths. It has been widely used as a marker to set them apart from both earlier and modern humans.
The skull at the center of this study, known as Xujiayao 15, was found along with an assortment of other human teeth and bone fragments, all of which seemed to have characteristics typical of an early non-Neandertal form of late archaic humans.
Trinkaus, who has studied Neandertal and early human fossils from around the globe, said this discovery only adds to the rich confusion of theories that attempt to explain human origins, migrations patterns and possible interbreedings.
While it’s tempting to use the finding of a Neandertal-shaped labyrinth in an otherwise distinctly “non-Neandertal” sample as evidence of population contact (gene flow) between central and western Eurasian Neandertals and eastern archaic humans in China, Trinkaus and colleagues argue that broader implications of the Xujiayao discovery remain unclear.
“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 said. “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.”
Well quite interesting research indeed , but the evolutionary look to the subject matter is more complicated than `Interbreeding` conclusion or suggestion . Let me go to the `evolutionary` specific details if I may :
The lateral or horizontal canal (external semicircular canal) is the shortest of the three canals . Movement of fluid within this canal corresponds to rotation of the head around a vertical axis (i.e. the neck), or in other words rotation in the transverse plane . This occurs, for example, when you turn your head to the left and right hand sides before crossing a road
It measures from 12 to 15 mm., and its arch is directed horizontally backward and lateral ward; thus each semicircular canal stands at right angles to the other two. Neanderthals lived in Icy climate –not like hot Africa of course –
Bipedal (human) walk on ice and in order to balance himself of herself is strictly dependent on “early and accurate sensation of minute rotation(spin) in the `vertical axis` by the stimulus of Lateral(Horizontal) Semicircular canals” –Neanderthals have had to survive on icy climate – so the Bipedal ice walking by Neanderthals –even with the help of stick(cane) as 3rd support point on ice might have been used – which is utmost important for survival (disability or death due to fall and fracture of bones ) , those does not have that capability – with large diameter lateral(Horizontal) Semicircular canal of vestibule (means early warning of angular rotation of endolymph inside the semicircular canal due to large radius and angular momentum . In other words `larger the radius` of the Lateral(Horizontal )Semicircular canal more sensitive it would be ; to the stimulus of angular motion (spin in vertical axis) simply because the displacement of end lymphatic gelatinous fluid with floating otoliths at the periphery will be more `pronounced – longer length motion at the periphery(endolymph fluid) /per degree of angular rotation ` of the body during a early spin . The stimulus of `hairy cells` of vestibule is directly correlates with the floating otolith`s “ relative displacement in a given time” and the angle of rotation , larger radius semicircular canal will `accelerate and displace ` the endolymph fluid and floating otoliths ` in a given time much more significantly at the periphery of larger diameter semicircular canal ` compared to smaller radius semicircular canal . Which means `Early warning of fall` …! and more time for the `crucial` protective posture change to lessen potential damage of fall on ice .
Earlier the warning of vertical axis`spin` on ice means : Longer time for the preventive(protective) defensive posture to take and balance back to prevent potential fall (disability fracture and ultimate death) .
So those who has Large Radius Lateral(Horizontal) Semicircular canals in their inner ear vestibules `will clearly have significant survival advantage` on icy cold environment with frequent `vertical axis spins` and falls .
This is exactly the fundamental evolutionary reason why Neanderthal`s Temporal petrous bone labyrinths (* ) has `prominent` and large Lateral(Horizontal) semicircular canals . Icy environment locomotion –ice walking- is the answer .
Now the punch line is : Whether Eastern Eurasian Pleistocene Humans has had INTERBREED with Neanderthals as they imply at the research article OR they(Eastern Eurasian Humans) themselves seperately developed similar Large prominent Lateral(Horizontal) semicircular canals exactly like Neanderthals needs to be answered here , since Eastern Eurasian Humans also lived in Icy cold environment they might also have selectively ( separately and independently in a different geography but similar Icy Environment ) had evolved QUITE SIMILAR Lateral (Horizontal) semicircular canals at their Temporal petrous labyrinths exactly like Neanderthals did … ICY ENVIRONMENT THEY LIVED IS THE COMMON DENOMINATOR FOR BOTH –Neanderthals and Early Eastern Eurasian Humans for sure . In other words the evolutionary Temporal petrous labyrinth difference and/or similarity has nothing to do with Head and Neck and body locomotion differences BUT the` ice walking ` and `balance on ice ` the Environment they have to survive in …
( * ) http://www.eva.mpg.de/evolution/staff/hublin/pdf/Spoor-et-al03_Neanderthal-labyrinth.pdf BONY LABYRINTH OF NEANDERTHALS