Traces of unknown species found in modern human DNA

(ORDO NEWS) — A new computer algorithm has reconstructed the genetic history of the Neanderthals and Denisovans.

Biologists have found in the DNA of the Neanderthal and Denisovan man traces of unknown human species that once crossed with them. Part of this genetic heritage is also carried by modern people.

The achievement is described in a scientific article published in the journal PLoS Genetics.

Scientists have long been studying DNA found in fossils to reconstruct the lineage of humanity. Thus, it is known that the representatives of Homo sapiens that came out of Africa interbred in the vastness of Eurasia with Neanderthals and Denisovans. The last two species became extinct (most likely, not without our help, although there are different opinions), but their “genetic gifts” remained in the genome of modern people.

And what is the genetic history of the Neanderthals and Denisovans themselves ? Was H. sapiens the first human species to interbreed with? Or did they, too, carry in their DNA the legacy of the departed branches of the human race and, perhaps, passed it on to us?

It is difficult to answer this question, because very few samples of Neanderthal and Denisovan DNA have been found. Until recently, it was only firmly established that these two species interbreed with each other.

Now a trio of researchers from the United States has presented a new method for analyzing ancient genomes that can reconstruct the ancestry of species even from such scanty data.

The new algorithm is called ARGweaver-D and is an advanced version of the well-known ARGweaver tool. The user of the new version selects a demographic model, including, for example, information on the settlement and migration of the desired species. Based on this data, the computer analyzes the genome and reconstructs the history of crosses.

The authors tested their brainchild on the genomes of modern humans, Neanderthals and Denisovans. The program correctly recognized all known crossing events between these species. Then biologists stepped into unknown territory, undertaking the reconstruction of the genealogy of the Neanderthals and Denisovans themselves.

Scientists analyzed DNA from the remains of two Neanderthals, one Denisovan and two H. sapiens from Africa.

Calculations showed that 3% of the genome of Neanderthals got into their DNA as a result of crossing with an unidentified human species. And it happened 200-300 thousand years ago.

The Denisovan also carried a “genetic present” from an unknown species. About 1% of his genome was acquired by crossing with someone unknown.

Not all “alien” genes inherited by the Neanderthals and Denisovans ended up in the genome of modern humans as a result of our crossing with them. However, 15% of their total “acquisitions” still ended up in our DNA.

It is difficult to judge what traits of modern people these genes are responsible for and how useful they are to us. In any case, they are not harmful: experts have not found any traces of negative selection acting on these genes.

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