Skull with a million years gives surprising clues about our enigmatic ancestor X

The common ancestor of Homo sapiensNeanderthals and denisovans could be much older than thought – a discovery that can completely transform the way we understand human evolution.

The origins of human beings may retreat From what was thought, and it can apply to our extinct cousins, neanderthals and the denisovans.

According to a new analysis of fossils, presented in a published Thursday in the magazine Sciencethe ordinary ancestor of the three groups will have lived over a million years ago – more than twice than now has been admitted.

“If we are certain about these branch points so old, it means that we are losing a huge part of the initial history of these lineages,” says Chris Stringerresearcher at the Natural History Museum of London and corresponding author of the article, quoted by.

Results can help solve the search for the so -called “Ancestor X”, The population that gave rise to modern humans, neanderthals and the denisovans, and raise the hypothesis that the denisovans were our closer relatives – even more than neanderthals –although not all researchers agree with this interpretation.

During the study, Stringer and his team, which includes Xijun Niresearcher at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing reevaluated one in Central China.

In 1989 and 1990 two partial skulls had been discovered on a terrace over the Han River. Both skulls They were quite deformed for the time spent underground, but or second, designated Yunxian 2was in better condition.

Researchers resorted to the latest techniques to rebuild the skull, including methods based on Computerized tomographythat allow digitally separate bone fragments from the rock matrix and surrounding sediment.

The skull “It is long and low, with a pronounced supraciliary arc“Describes Stringer.” There is still a nose somewhat damned, big teeth, but third small molars. “

The Yunxian 2 skull will have between 940 thousand and 1.1 million years. The hominids of this time are usually classified as Man alertspecies emerged in Africa about 2 million years ago and spread across southern Asia, including Indonesia, where he will have survived up to 108,000 years ago.

However, Stringer argues that This fossil does not fit this profileas it has several characteristics closer to later groups, such as Neanderthals.

To clarify their classification, the team compared Yunxian 2 with 56 other hominid fossils. The analysis of cranial forms allowed to establish a genealogical tree where similar fossils were grouped.

Of this exercise resulted Three great branchescorresponding to most fossils of the last million years: Modern humans (Homo sapiens) bone Neanderthals (Homo Neanderthalensis), who inhabited Europe and Asia until about 40,000 years, and the Denisovanosafrom East Asia.

Denisovans were first identified in 2010 through DNA extracted from a bone fragment. But it was only 15 years after it was possible to associate more complete fossils with this group.

Stringer participated in Description of a skull found in Harbinin China, classified as A person longthat based on molecular evidence in June this year. Yunxian 2 seems to correspond equally to a primitive denisovan, such as other Asian fossils.

“It is important to bring together all these fossils under the denisovaana lineage”, comments Aylwyn Scallygeneticist at Cambridge University, who did not participate in the study. “So we can better understand where they lived, how they were and what kind it was about.”

The identification of Yunxian 2 as Denisovano rewrite the history of evolution recent human in two ways. Firstly, it alters the narrative about how the three populations emerged.

So far, genetic analyzes indicated that an ancestral population – the Ancestor X – would have divided into two: One gave rise to modern humans and the other originated Neanderthals and Denisovans, who only later separated with each other.

In this new reconstruction, however, they were Neanderthals the first to move awayabout 1.38 million years ago, while modern humans and denisovans would have only been separated 60,000 years later, 1.32 million years ago. If this version is correct, Denisovans would have been our closest relatives “Not the Neanderthals, as genetics suggests.”

Scally, however, is skeptical. Part of the doubt is due to the fact that history of these populations be complex. “It is not well described by a simple tree, such as the one used by the researchers, but by a intertwined network,” he explains.

In addition, it recalls, Genetics is a more reliable tool than morphology to infer kinship relations – especially when only incomplete fossils – and in this field genetic data point out in a clear direction.

The second major implication is that all these groups They are much older what was thought.

So far, genetic studies suggested that the ancestors of modern humans had separated from the parent of Neanderthals and Denisovans between 500,000 and 700,000 years ago. But Yunxian 2 points out the denisovans to be a distinct lineage for over a million years.

Scally admits that there may not be a single date for these divisions, which may have been long processes, with episodes of separation and rapprochement. In this scenario, the divergence may actually have started over a million years ago, but long hundreds of thousands of years to consolidate.

This widening of the chronology raises New questions. The oldest known fossils of our species are about 300,000 years old. Where are the ancestors for a million years? “Or we haven’t found themor are there and were not recognized as such, ”says Stringer.

Nor is it known what the X Ancestor would be likenor where you will have lived. “Ten years ago, I would have said that probably Africa would be the origin of most of these groups,” Stringer admits.

“But today it seems more plausible than this ancestor lived outside Africa, Perhaps in Western Asia. This would imply that the sapiens remote ancestor then entered Africa and has evolved over most of the million years, ”he concludes.