Old teeth allude to a mysterious human parent in China

Scientists scratch their heads in four caves found in a cave in Tongzi County, southern China.

In 1972 and 1983, researchers extracted the old teeth of about 200 000 years from the silty sediments of the soil of Yanhui Cave, initially tagging them Homo erectusthe hominins who stand up were the first to leave Africa. Subsequent analysis suggested that they did not quite fit Homo erectus, but it is there that the story has stopped for nearly two decades.

Now, a study published in the Journal of Human Evolution take a fresh look at these ancient teeth using modern methods to examine curious remains. The new analysis excludes the possibility that the teeth come from Homo erectus or the more advanced Neanderthals, but the elusive owner remains unknown.

"It's strange, we do not know where to put it," says study author Song Xing of the Beijing Institute of Paleontology and Paleoanthropology of Vertebrates.

The four teeth join a growing number of discoveries in China that do not perfectly match the known branches of the tree of human evolution, suggesting that there is more in the history of humanity in this region.

"We still think that Africa is the" cradle of humanity, "explains the author of the study María Martinón-Torres, director of the National Center for Investigation on the Evolution of Human Society. Spain. "I would say it's a cradle of a probably human species, which is Homo sapiens. "But many human species have already walked the Earth and what is happening in Asia," she says, "is probably" crucial to understanding the bigger picture ".

The history of humanity has become more and more complex in recent years, with ever more chapters and characters added to the mix. Migration from Homo erectuslike hominines began about two million years ago, as evidenced by the surprisingly old tools recently recovered in central China. In the hundreds of thousands of years, other groups have continued to roam the world and disperse their remains.

As these early adventurers made their way into foreign countries and climates, they diversified and diversified. Neanderthal precursors have spread to Europe and the Middle East. Other hominines have moved to Southeast Asia, giving rise to the Homo floresiensis in present day Indonesia and stone tool users from the Philippines.

So where are Tongzi's teeth? "We only have a very small number of these materials," Xing says cautiously. "But now we can put a little imagination."

The latest study discusses the structures and patterns of Tongzi's teeth, detailing their surfaces and bowels with the help of a method known as micro-computed tomography. The team compared its data to older and more modern dental samples from Africa, East Asia, West Asia and Africa. ;Europe.

They discovered that Tongzi's teeth are a patchwork of ancient and modern traits. In particular, the tissue under the enamel, called dentin, is devoid of the revealing wrinkles found in the teeth Homo erectus. Most teeth have remarkable simplicity and are similar to those of later teeth. Homo species like Neanderthals. But overall, the characteristics of the teeth do not match any of these categories.

An interesting possibility is that the teeth could come from the enigmatic group of hominins known as Denisovans, who would have separated from Neanderthals at least 400,000 years ago. Known for only three molars, a little finger and a fragment of skull recovered in a single Siberian cave, the group is better recognized by its genetic fingerprints. Traces of Denisovan DNA persist in modern peoples all over Asia, especially among the populations of Oceania.

Paleoanthropologist Bence Viola of the University of Toronto, who revealed Denisovan's skull fragment last week during a clashing meeting of anthropology in Ohio. While the teeth seem large enough – a notable feature of the Denisovans – the limited physical remains make it difficult to say anything more definitive without genetic evidence. And preserving the delicate structure of DNA poses a challenge in the heat and humidity of southern China.

"It's clearly a distinct population. It is not clear that they belong to Denisovans, "says Viola, who is also part of the Siberian branch of the Russian Academy of Sciences.

Shara Bailey, a dental paleoanthropologist at New York University, is skeptical about Denisovan's affinity for this particular sample. "I'm sure there is Denisovan material on the market," she says. "The problem is that until we have a good comparative cranial and mandibular material, it's just a guessing game."

Another possibility is that the new Chinese fossils come from a hybrid lineage. Several groups probably crossed over this period and, each time the hominines mixed, they seemed to cross each other. Last year again, scientists identified a bone fragment from an older teenager who had a Neanderthal mother and a Denisovan father.

When the Denisovans ancestors ventured into Asia, for example, they could have met the already present population, Homo erectus, and hybrid to create a group that produced Tongzi's teeth, says Viola. A mystery in Denisovan's DNA could support this suggestion: Previous genetic analyzes suggested that a small percentage of Denisovan's DNA came from an unknown but extremely ancient hominin. But without the DNA of Tongzi's fossils, scientists have always guessed.

For the moment, the study represents an important step in the discovery of the full extent of human history. While researchers have long studied these Chinese fossils, the results are often not translated into English, which limits its integration into the larger picture, notes Chris Stringer of the Natural History Museum in London. In addition, says Bailey, access to Chinese fossils has been limited, which has limited scientific understanding.

But now, this is changing and the more scientists seem to look, the more they seem to find the complexity. A variety of other Chinese fossils dating from 360,000 to 100,000 years ago also do not fit into neat boxes. These include teeth with surprisingly advanced features from Panxian Dadong in southern China and robust chompers found at the Xujiayao site in northern China.

Then there are the skull fragments. A particularly intriguing sample is a remarkably complete skull from Harbin, China. Although this is not yet described scientifically, his features represent an older face than that of a Neanderthal, so that he could belong to a group that has branched out early from this line, note Stringer.

"I think there is something separate in China – even without DNA, I think we can say," says Stringer. But for more details, scientists will need more evidence.

As Kristin Krueger of Loyola University says by email, the study "highlights a cultural shift in paleoanthropology – a change that acknowledges that our story is much more complex and complex than we do it. imagined – and our story is constantly changing. "