Modern humans carry DNA from strange relatives

dna 1903318

Modern humans also carry Denisovan DNA, an archaic hominid that occupied Siberia

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Reconstruction of the appearance of a young Denisovan woman based on DNA analysis of remains of this hominid. Maayan Harel, CC BY-SA
José Mora Perujo, Malaga University and Delphine Pott, University of Tübingen

The DNA we possess comes in equal parts from our father and our mother. But, in addition, our cells still contain genetic material from ancestors who occupied the Earth hundreds of thousands of years ago.

Like all other species, we are sons and daughters of evolution. We inherit and bequeath to our offspring genes from archaic human species, such as Neanderthals, and also Denisovans, a group of hominids that occupied Siberia and part of Asia, and interbred with our ancestors 50,000 years ago.

Among other things, Evidence has been found that Denisovans lived at high altitudes in Tibet, and they were the carriers of a gene that helps modern people cope with similar elevations.

The mother we share: the “mitochondrial Eve”

How does this archaic genetic material reach us?

In the fertilization, the egg and sperm merge into one. The combination of the genetic material of both will be the DNA of the individual who is born, his own genetic fingerprint. But a fact that is often forgotten is that the mitochondria, organelles present in all cells, come only from the egg. They come directly from our mothers, without combining with genetic material from the father.

Thanks to that mitochondrial DNA we can travel back in time, through maternal lineage .

Molecular clocks They are certain genes that allow us to measure the rate of changes (or mutations) that they have suffered over time. counting changes, it is possible to know the age of an individual and establish relationships between ancient and current species.

Thanks to molecular clocks and mitochondrial DNA we know that all living human beings have the same ancestor. The call Mitochondrial Eve It was a woman (Homo sapiens) African who lived about 200,000 years ago. She was the carrier of the mitochondria from which all people in the current human population descend.

We carry in our mitochondrial DNA the echo of that first woman.

The lineage of Homo sapiens

The human species began in Africa about three million years ago. Since the Australopithecus until the Homo sapiens There have been many humans of different species, including Neanderthals and Denisovans.

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Migration map Homo sapiens, Homo erectus and Homo neanderthalensis NordNordWest/Wikimedia Commons

The sequencing of the human genome, which allows us to know the sequence of all the genes, has allowed, among other things, to study and compare the genetics of modern man with our ancestors. Currently, and thanks to modern sequencing techniques, it has been possible to obtain the genomes of archaic and extinct species of hominids, such as those mentioned above.

In 2021, the gene sequences of 23 archaic humans were known (18 Neanderthals, four Denisovans, and a woman descended from a Neanderthal mother and a Denisovan father).

Both species interacted with modern men, Homo sapiens, since the 2 % in the genomes of non-Africans comes from Neanderthal men.

Furthermore, 5 % in the genomes of Oceanian populations dates back to Denisovan men, and the presence of this archaic species can still be detected in the genome of current Asian populations. This presence in the genome of modern man also allows us to obtain very valuable information about the biology of our origin.

He Homo neanderthalensis It is a particular case, since his mitochondrial DNA has not been found in it Homo sapiens. There are currently several hypotheses to explain this, but the fact is that we do have Neanderthal genes. For example, in Europe the contribution of Neanderthal genes to skin color reaches up to 70 %. Searching for variations in the genomes of Mesolithic hunter-gatherers (about 10,000 years ago) it has been found that the Lighter skin color in modern Europeans was not very common until the Neolithic (about 5,000 years before our era).).

Reconstruction of a Neanderthal man.
Reconstruction of a Neanderthal man. frantic00 / Shutterstock

The finger of a Denisova girl

In 2010, mitochondrial DNA was sequenced from a girl's finger, found in the Denisova caves, in Siberia (Russia). This allowed the identification of a new hominid: Denisova man. The surprise was that the 17 % in its genome was Neanderthal DNA, so both species interbred at some point in evolution. This was confirmed when a piece of bone from another individual who lived about 90,000 years ago. This individual was special, since his father was Denisovan and his mother was Neanderthal: we found the first hybrid individual of these two species. This could indicate that the relationship between these two species was not something specific.

Analysis of the genes that determine blood groups indicates that both Neanderthals and Denisovans had African origins.

Also interesting is the presence of a variant of the gene for Rh factor in Neanderthals who It has only been found in some individuals from Oceania, giving clues about possible crossings with Homo sapiens before its expansion towards Southeast Asia.

That same study suggests that the low genetic variability of Neanderthals would make them more prone to certain diseases. Their extinction could have been determined by genetic problems, which made them more prone to viral infections and a low reproduction rate.

Svante Pääbo, the father of paleogenetics

All of these studies have been important for the scientific community. One of the most representative faces of this field is that of Svante Pääbo, whose contributions to human evolutionary genetics have been of vital importance. So much so that in 2022 he received the Nobel Prize in Physiology or Medicine “for his discoveries about the genomes of extinct hominids and human evolution.”

The possibility of studying archaic DNA meant a revolution in understanding the origin of our species. We are hybrids, the result of crosses produced millions of years ago, when we did not even exist.The Conversation

José Mora Perujo, Predoctoral researcher - Molecular Biology and Biochemistry., Malaga University and Delphine Pott, Postdoctoral fellow, University of Tübingen

This article was originally published in The Conversation. read the original.