Gene trace of a human puzzle species

The unknown primitive emerges like a shadow. (Image: borchee / iStock)

The Neanderthals and the Denisova people “mixed in” with the Europeans and Asians. Similar things are emerging in the case of West Africans, researchers report: According to the ancestors of certain population groups, mysterious archaic people have left their inheritance. It remains unclear who these creatures were, since the results are based on an indirect detection method: the puzzle species has so far only been found in the genome.

Studies in recent years have already made it clear that there have been fruitful quarrels between modern humans and their cousins, who still existed in parallel. When Homo sapiens immigrated from Africa to Europe and Asia, he mingled with the human forms already living there – with the Neanderthals and the Denisova people, respectively. These crossings resulted in a few percent of “archaic” DNA in the genetic makeup of today’s Europeans and Asians, and in lesser traces also in Africans, as a study recently revealed. The results are based on direct comparisons, since the genes of the Neanderthals and the Denisova people have been preserved and therefore could be reconstructed.

Have there been hybridizations in Africa?

However, it is unclear to what extent archaic human forms also mixed with the ancestors of today’s African people. One reason for this is that in the hot climate, no remains of genetic material have been found in finds of hominins that are suitable for genetic comparison. However, modern genetics meanwhile offer alternative means of detection: from certain patterns in the genome of humans, numerous conclusions can be drawn about former population developments. Even before the current study, there were reports of genetic references to archaic human forms, which apparently existed in parallel with modern people in Africa and mixed with them.

Arun Durvasula and Sriram Sankararaman from the University of California at Los Angeles are now presenting the clearest evidence of these mysterious processes in early human development in Africa. They used a special computer modeling technique to analyze genetic sequences in order to track down pieces of archaic DNA in the genome of modern humans. As part of their study, they examined 405 genomes from the West African population groups of the Yoruba and Mende. They compared the results of the analysis with the results of the genomes of Neanderthals and Denisovans, whose archaic signature is known.

The trace of a ghost population

As the scientists report, they encountered genetic sequences in West Africans that also came from archaic people who apparently once mingled with their ancestors. According to this, 2 to 19 percent of the genetics of the Yoruba and Mende come from this mysterious archaic human form. However, your identity remains unclear. According to the researchers, however, their data nevertheless show that it was hominins that had split off from the human family tree before the Neanderthals and the Denisova man. This separation may have taken place a million years ago.

The researchers can only vaguely estimate when the crossing into the ancestors of today’s West Africans took place. Possibly as early as 124,000 years ago – however, later mixing also seems conceivable. “One explanation for a more recent period of introgression would be that this archaic human form in Africa has long existed parallel to modern humans,” write Durvasula and Sankararaman. “Alternatively, the archaic population could have interfered earlier in a modern human population, which later connected with the ancestors of the populations that we analyzed here,” said the researchers.

As they explain, there are indications from archaeological finds that support their results, although no genetic remains are available for direct genetic comparisons:
Human fossils have been found in Africa and the Middle East in recent years, which up to 35,000 years ago have combinations of archaic and modern human characteristics. According to the researchers, this could be evidence of the complex history of the interaction between modern and archaic hominins in Africa.

According to Durvasula and Sankararaman, an ever more exciting field of research in the field of anthropology is emerging: “A detailed understanding of the intermingling of modern humans with archaic forms and their importance in adapting to different environmental conditions now requires an analysis of genomes in the entire geographic area of ​​Africa “, The researchers conclude.

Source: Science Advances, doi: 10.1126 / sciadv.aax5097

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