TWO 100,000-year-old skulls unearthed in China are up-ending ideas about human evolution. They appear to be hybrids of humans, neanderthals — and a third mysterious race.

The partial skulls, unearthed at the Lingjing excavation site in Xuchang, central China, offer new evidence of the behaviour and distribution of pre and early human populations in Eurasia.

And it’s largely unexpected.

They display the large brain capacity, lightly-built cranial vaults and modest bone rides on the brow, similar to early modern humans.

They display a low and board braincase which rounds on to the inferior skull (underside of the skull), as with Middle Pleistocene early Eurasian humans.

They have semicircular structures in the inner-ears and an arrangement of the rear skull similar to that of Eurasian Neandertals.

Put together, these three separate and distinct traits suggest an intermixing of existing human ancestors.

“I don’t like to think of these fossils as those of hybrids,” study co-author and anthropologist Erik Trinkaus says. “Hybridisation implies that all of these groups were separate and discrete, only occasionally interacting. What these fossils show is that these groups were basically not separate. The idea that there were separate lineages in different parts of the world is increasingly contradicted by the evidence we are unearthing.”

DENISOVANS UNMASKED?

A fragment of a fingerbone found in a Siberian cave first alerted the world to the existence of an extinct ice-age human species in 2010.

Since then, only a few more fragments have been found.

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But the AAAS news magazine Sciencemag is speculating these two new skulls may be our first good look at a Denisovan.

While the related journal article doesn’t mention the name, palaeoanthropologist Christ Stringer of the Natural History Museum in London is quoted by the magazine as saying: “everyone else would wonder whether these might be Denisovans.”

A new paper in @sciencemagazine could shed light on the mysterious, ancient Denisovans: https://t.co/YvqkFaw6jC — News from Science (@NewsfromScience) March 2, 2017

Sciencemag quotes palaeoanthropologist Maria Martinon-Torres as saying the skulls “definitely” fit expectations about Denisovans ... “something with an Asian flavour but closely related to Neandertals.”

What few Denisovan remains have been found have dated from 100,000 to 50,000 years ago. Their DNA paints a picture of a species isolated for hundreds of thousands of years before mixing with Neanderthals and modern humans..

This is exactly what the DNA tells us when one tries to make sense of the Denisova discoveries,” palaeoanthropologist Jean-Jacques Hublin of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, says. “These Chinese fossils are in the right place at the right time, with the right features.”

RAISED EYEBROWS

The two skulls were unearthed in the city of Xuchang in Central China in 2007 and 2014. They date from between 105,000 and 125,000 years.

Modern humans first appeared in Africa about 150,000 to 200,000 years ago. Their first migration out of Africa is believed to have started 100,000 years ago.

Neanderthals occupied Europe and Asia from 200,000 to 40,000 years ago.

The world of 100,000 years ago was a particularly important time for the evolution of Homo sapiens. But the fossil record for the time is relatively scarce.

What genomics has taught us about human evolutionary history and the peopling of the world - review in @nature https://t.co/8NKhTLBMul pic.twitter.com/Y016oBlzG4 — NatureEcoEvo (@NatureEcoEvo) January 20, 2017

In recent decades, unusual finds have suggested the presence of other forms of ancient hominid living in Europe and Asia

There’s the mystery of Peking man. There’s the unexplained Dmanisi hominins. Then there’s the strange Denisovans.

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Whatever their origin, the new skulls paint a much more confused picture than the traditionally accepted one of separate populations living largely independent of each other.

It all adds up to a growing rethink of the whole ‘out of Africa’ theory.

Some academics argue that modern humans may have evolved at the same time in Africa and several spots in Eurasia from the interbreeding of common ancestors.

‘MOSAIC MAN’

The two Xuchang skulls are being described by researchers as holding a ‘mosaic’ of human traits. Some are old. Some are new. Some are in-between.

Because the skulls are only partial, the hominin’s complete form remains a mystery.

We don’t know how tall it was. We don’t know if it was well-built, like a Neanderthal, or more delicate — like a Denisovan.

Nor has any portion of the face — including a jawbone — yet been found.

This means we don’t even know what they looked like.

Do these #fossils from China finally put a face on the elusive Denisovans?! An exciting possibility! https://t.co/nOr7wlSRI0 #hominins pic.twitter.com/hwKgN31Arm — Paige Madison (@FossilHistory) March 2, 2017

But we know they had big brains. And the low brow ridges suggest more refined features than a Neanderthal.

There is hope of finding out more. The fragments of the skull that have been found have in other skeletons preserved traces of DNA. Extracting this would be the subject of future research.

Meanwhile, excavations are continuing in the region of Xuchang in the hope that more complete examples of the ‘mosaic’ hominid will be found.

The research was detailed in the March 3 edition of the journal Science.