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Traces of an unknown ancestor found in the human genome

Traces of an unknown ancestor found in the human genome 1

In early August, American researchers identified traces of a previously unknown ancestor in human DNA. Apparently, the ancient Sapiens interbred not only with Neanderthals and Denisovans, but also with someone else. Probably with Homo erectus – his genome has not yet been deciphered. 

Scientists have previously mentioned a mysterious archaic species that left an admixture in the DNA of Melanesians and modern Africans. Who is this mysterious hominid and what modern people have inherited from him.

Alien genes

In 2016, experts from the University of Texas at the annual meeting of the American Society of Human Genetics stated : traces of hominids unknown to science were found in the DNA of Melanesians living on the Pacific Islands. Comparison of their genome with the DNA of Neanderthals, Denisovans and Africans led to this conclusion.The researchers were going to find out what percentage of genes we inherited from extinct Homo. And they unexpectedly discovered that a significant part of the ancient genes, considered Denisovan, actually belong to another species of man.In the same year, Danish scientists made similar conclusions – regardless of the Americans . After analyzing about a hundred genomes of Papua New Guineans and Australian aborigines, they noticed an admixture of archaic DNA. At first glance, it resembled Denisov’s one, but judging by some differences, it was a question of a different kind of hominids.

Ati (Philippine Islands)
CC BY 2.0 / Ken Ilio /In 2016, scientists found traces of an extinct ancestor in the DNA of Melanesians, which could belong to an as yet undescribed hominid species.

Traces of unknown people

The 2016 studies raised many questions: the genome of a modern person, from whom they were looking for foreign genes, was compared with the DNA of those from whom he could get them.By that time, the genome of the Neanderthals had already been well studied, but the main source of information about the Denisovans was the phalanx bone of the finger and several teeth from the Altai cave. Given that Homo sapiens are believed to have mingled with Denisovans who lived in southern Asia or eastern Indonesia – distant populations often differ from each other – the traces of the mysterious hominid could well belong to them.

Scientists believe that Homo sapiens and their ancestral population have crossed several times with representatives of other Homo species. Thanks to this, there are sections in the DNA of modern people inherited from both Neanderthals and Denisovans.However, four years later, researchers from the University of California at Los Angeles, proposed a new method for finding an ancient impurity in the DNA of modern people. It was no longer required to know the genome of the person from whom it was inherited. That is, scientists could find traces of hybridization of our ancestors with extinct species of Homo, from which nothing remained – no bones, no teeth, no tools.The first to test the new approach were the West African Yoruba and Mende peoples. Experts analyzed 405 of their complete genomes and isolated from two to 19 percent of previously unknown archaic DNA. This means that the ancestors of modern Africans interbred with the species of people that separated from the common trunk about 625 thousand years ago – before the appearance of the Neanderthals and Denisovans.

Yoruba musicians (Nigeria)
CC BY 2.0 / Melvin “Buddy” Baker /The ancestors of the West African Yoruba tribe interbred with so far unknown species of people who separated from the common trunk about 625 thousand years ago.

Demographic modeling showed that hybridization took place no later than 43 thousand years ago – approximately at the time when in Europe Neanderthals began to mix with Homo sapiens.True, what exactly the genes transmitted by the mysterious ancestor are responsible for, and what role they played in the survival of the West African peoples, is not yet clear.

Mysterious ancestor

Six months later, scientists from Cornell University,  applied a similar technique when analyzing the genomes of two Neanderthals, one Denisovan, and two modern humans. As a result, it turned out: ancient hominids of different species entered into sexual relations and exchanged genes whenever the two groups crossed in time and space. There are probably more cases of crossing than is commonly believed.So, Neanderthals had a sexual interest not only in sapiens: about 200-300 thousand years ago, they mixed with an unknown ancient species of hominids and inherited from them almost three percent of the genome.

In addition, traces of hybridization were found in the DNA of the Denisovan man – one percent of the genome came from a mysterious archaic relative. And then, thanks to the crossing of Denisovans and Homo sapiens, 15 percent of these genes were passed on to modern people.The authors of the work suggest that we are talking about Homo erectus, the direct ancestor of the Sapiens, who could have lived in Eurasia simultaneously with the early Neanderthals and Denisovans. True, it is impossible to prove this: researchers have not yet received and sequenced his DNA.

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