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Svante Paabo, a Swedish biologist, was awarded the Nobel Prize in Physiology and Medicine for his discovery of the genomes of Neanderthals and Denisovans. His methods contributed to the development of paleogenomics, the study of the DNA of extinct human and animal species.
The Homo sapiens human species is part of the hominidae family and the hominin subfamily, which also includes numerous extinct ancestors.
Approximately 6 million years ago, our last common ancestor with chimpanzees was in Africa. About 4 million years ago, the genus Australopithecus emerged, the ancestor of humans. Approximately 2.5 million years ago, the Homo genus emerged from Australopithecus. In the past 1.8 million years, people of the species Homo erectus left Africa and settled throughout the world. In Eurasia, a number of human species descended from them, including Neanderthals and Denisovans. In the meantime, evolution took place as usual and Homo sapiens emerged on the Black Continent. Homo sapiens is known to have originated in Africa about 300,000 years ago. They spread around the globe. Meanwhile, the rest of the species went into extinction.
Is there any genetic difference between Neanderthals and other indigenous inhabitants of Eurasia? Did the sapiens who came from Africa assimilatize those species? If not, are there at least a few genes from ancient Eurasian species in modern man? We owe the answers to all of these questions to the current laureate.
The hacking of DNA
A daunting task, not only in importance but also in difficulty, is extracting and reading the genome of ancient bones. DNA molecules are fragile and break down over time due to chemical changes. After tens of thousands of years, only a small amount of the original DNA remains in the samples. However, microbes, modern humans and other species introduced DNA in abundance.
As a student, Svante Paabo began to work on this problem even before the modern human genome could be decoded. In 1997, Paabo achieved an impressive success – he deciphered mitochondrial DNA from a Neanderthal bone discovered back in the 19th century. The work of the scientist lasted decades.
Almost all of the DNA of human cells is found in the nucleus, but mitochondria, which provide energy to cells, also have their own genomes. As far back as billions of years ago, mitochondria were separate organisms that settled into cells symbiotically. Mitochondrial DNA is short, so it is not very informative. As there are thousands of mitochondria in a cell, each has a DNA molecule, and all of these molecules are the same. This makes it easier to extract and decode. As if one word is printed several thousand times on the page. Despite the fact that the text has almost entirely been erased, it is still possible to preserve the cherished words. Paabo and his co-authors managed to achieve this.
A matter of blood
After founding the Institute for Evolutionary Anthropology of the Max Planck Society in 1999, the future laureate assembled a group of like-minded scientists and began to work on decoding the “real” Neanderthal genome. The methods for isolating and analyzing ancient DNA have been stubbornly improved over the years. Finally, in 2010, Neanderthal nuclear genomes was deciphered.
Researchers compared the genomes of Neanderthals and modern humans and found out a lot of interesting things. Despite our existence, Neanderthal genes are very few: according to various estimates, 1-4% of our genome is Neanderthal. Because Neanderthals were not assimilated by sapiens, they still interbred with them occasionally. Indigenous Africans, on the other hand, do not possess Neanderthal genes. Since Neanderthals are a European species, this is not surprising. Thus, the natives of the Black Continent are the last purebred Homo sapiens.
The genes of the Neanderthal species aren’t just a souvenir from an extinct species; they play an important role in the formation of our immune system, for example.
The Altai cave riddle
Approximately 40,000 years ago, a finger phalanx was discovered in Denisova Cave, Altai. Since it was a relatively small fragment, it was difficult to determine who the ancient cave dweller was. However, the DNA contained in the fossil bone is surprisingly well preserved. As a result of Paabo’s team’s decoding of this genome in 2010, it turned out that he is neither sapiens nor Neanderthal. Thus, another species of human being was discovered – the Denisovan man.
So far, a Denisovan skeleton has not been found in its entirety. The finds are fragmentary: the same phalanx, teeth, a small piece of skull, but genes can provide a lot of information about its history. In contrast to Neanderthals, Denisovans apparently lived mainly in Asia. In addition to interbreeding with Neanderthals and Sapiens, Denisovan man crossed at least twice with Sapiens. Southeast Asians still carry the genes of the Denisovan man, from whom the Tibetans inherited the EPAS1 gene, which allows them to live at high altitudes.
Paabo’s paleogenetic methods can also be applied to analyze the DNA of extinct animals, such as mammoths. They are constantly being improved, and allow us to access the past of our own species and other species.
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