This new human lineage vanished also mated with modern humans

A new study reveals that a new missing human lineage who lived in New Guinea and who has crossed paths with modern humans

The genetic differences of this lineage compared to other humans make it a group as distinct as our nearest missing relatives, the Neanderthals and the Denisovans, the scientists added.

Although modern humans are now the only living branch of the human genealogy tree, others have not only lived alongside modern humans, but have even crossed with them, leaving behind a DNA in the modern human genome. These archaic lineages included not only the Neanderthals, the missing relatives of modern man, but also the mysterious Denisovans, known only from fossils found in the cave of Denisova in the Altai Mountains of Siberia.

Previous research has shown that, although Denisovans shared a common origin with Neanderthals, they were almost as genetically distinct as Neanderthals, just as Neanderthals were modern human beings. Previous work had estimated that the ancestors of modern humans were separated from the common ancestors of Neanderthals and Denisovans about 700,000 years ago, and that the ancestors of the Neanderthals and the Denisovans had diverged from one another. other around 400,000 years ago. [Denisovan Gallery: Tracing the Genetics of Human Ancestors]

In 2018, scientists discovered that Denisovans actually possessed more than one lineage. One was closely related to the Siberian Denisovan and has a genetic heritage found mainly in East Asia, while the other was further removed from the Siberian Denisovan and its DNA was mainly observed among Papuans and South Asians. These groups separated about 283,000 years ago.

To learn more about Denisovan's genetics, scientists analyzed 161 modern human genomes from 14 island groups in Southeast Asia and New Guinea.

The researchers found that large expanses of DNA from this geographic region did not fit into a scenario in which modern humans would cross there with a single line of Denisovan. Instead, they discovered that modern Papuans had hundreds of genetic variants of two profoundly divergent Denisovan lineages – one previously recognized in Papuans and South Asia and the other never identified before.

In total, "what we thought was one group – the Denisovans – was actually three very different groups, with a greater diversity among them than the one observed today among modern humans," he said. Lead author Murray Cox, Population Geneticist at Massey University in New Zealand, told Live Science. [In Photos: Bones from a Denisovan-Neanderthal Hybrid]

Based on the level of genetic differences between the three Denisovan lineages, the researchers suggested that the newly discovered line be separated from the other two about 363,000 years ago, Cox said. In total, this new Denisovan lineage "is about as different from the individual Denisovan found in Denisova's cave as that of Neanderthal," said Cox. "This means that if we call Neanderthals and Denisovans by special names, this new group probably also needs a new name."

The DNA of this new lineage has been found mainly in modern individuals who "lived in or near New Guinea," Cox said. "We used to think of the Denisovans as people who lived in the frozen north, for example around the cave of Denisova in Siberia – but their center of gravity was actually in the south, in the tropics of the Southeast Asia and New Guinea. "

Their main goal was not to learn about human evolution, but to promote modern human health.

"Our research program is focused primarily on improving health care for a region of the world radically under-researched," said Cox, referring to the tropics. In fact, archaic human research has been skewed in Europe and northern Eurasia, in part because DNA from ancient bones "can only survive in cold regions", said Cox. Until now, "the oldest DNA of the tropics is only 6000 years old".

Modern humans have inherited many genetic variants of archaic human crosses that "influence the health of people today, mostly positively, sometimes even negatively," Cox said. "For example, many Europeans have variants of Neanderthal immunity genes and these have been shown to be very important in the fight against infections today." If we retain archaic gene variants "It's usually because they're better than the modern human variant." We met with archaic hominins and we mostly took all the good pieces. "

And at least according to new discoveries, among the many different archaic human groups in Eurasia "most of them lived near the tropics," noted Cox. "If you look at modern human diversity, and biodiversity in general – for example, plants and animals – most of the diversity is in the tropics." This study fits into a much larger set of scientific discoveries that show that this was also true for archaic hominins – their center of gravity was also in the tropics. "

In the future, researchers will seek to use their findings to improve the health care provided to the inhabitants of the islands of Southeast Asia. "What are these archaic variants doing?" Why do we still have them? "How can we improve health care for 300 million people who have hardly ever conducted any health care research because they have not done so much? they are so biased in favor of people of European descent? " Cox said.

Scientists detailed their findings online today (April 11) in the journal Cell.

Originally published on Science live.

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