How the ghost of an extinct ancestor “lives” in us today

Protein variant will have passed the The man stood up Asian to the Denisovans, when the two populations met in Asia, possibly more than 400,000 years ago, a new study suggests.

For more than a century, the The man stood up it has proven its presence on several continents and has occupied a central place in the history of human evolution. With prominent supraciliary arches, it is known mainly through fossilized bones and teeth. But now, they are also a window into another ancient human group.

A new study in Nature this Wednesday claims that proteins preserved in the tooth enamel of fossils were found in China. And they have, at least, 400 thousand years.

The research, conducted by a Chinese team, analyzed six teeth assigned to The man stood up and revealed protein variants that also appear in Denisovans — an archaic human group known mainly through genetic remains — and in current human populations.

The discovery suggests that some people alive today may still be carrying a molecular inheritance of Asian populations of The man stood uptransmitted over time through crossings with other ancient human groups.

So far, recovery of DNA from The man stood up was considered practically impossible, highlights the . The species emerged around two million years ago and survived until approximately 110,000 years ago, which puts many of its fossils beyond the usual limit of DNA preservation. Furthermore, the extraction of genetic material can involve the partial destruction of rare fossils, which is why many museums and curators often refuse invasive sampling.

It was in this context that paleogeneticist Qiaomei Fu, from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, chose to seek proteins: they are more resistant than DNA and can persist for longer, especially when they are trapped in the mineral matrix of the teeth. Although they are not DNA, proteins result directly from the expression of genes and, therefore, can function as a kind of molecular substitute.

The team used a low-destructive technique known as acid etching. Instead of drilling or cutting teeth to extract bone or enamel powder, the researchers covered each tooth with an impermeable film, leaving only a small area of ​​a few square millimeters exposed. They then applied acid to that spot, removing enough material for analysis but preserving the overall integrity of the fossil, with only a slight change in color.

The teeth studied include fossils collected in the 1950s and 1960s in Gruta de Zhoukoudiannear Beijing, famous for its skulls The man stood up and isolated teeth, from two other locations in North and Central China. The analysis of enamel proteins made it possible to determine the sex of the individuals: five men and one woman.

Most importantly, researchers identified two specific variants in proteins involved in the formation of tooth enamel. One of them, AMBN-M273Vwas also found in Denisovan teeth and in modern humans, especially in populations with greater Denisovan ancestry, such as some communities in the Philippines and Melanesia.

The most likely explanation, for Fu, is that this variant passed the The man stood up Asian to the Denisovans, when the two populations met in Asia, possibly more than 400 thousand years ago. Later, the Denisovans transmitted this variant to modern humans who left Africa and arrived in Asia and Oceania around 50,000 years ago.

Not all experts consider this to be true. Diyendo Massilani, a geneticist at Yale University, points out that the protein analysis is solid, but that the chance of ancient crosses remains low. indirect. In theory, he explains, Denisovans and modern humans could have developed the same variant independently.

But other researchers consider the evolutionary explanation proposed by the team to be plausible. Kirsty Penkman, a geochemist at the University of York, notes that enamel proteins tend to vary little because they perform essential functions. For these experts, the study reinforces the idea that prehistoric Eurasia was inhabited by a diversity of human groups that coexisted, crossed paths and left marks on each other.

The second variant identified in the teeth, AMBN-253Gis not known in any other hominin or primate. If it turns out to be exclusive to the The man stood up Asian, could become an important molecular marker to follow the history of the species and its migrations across Eurasia.