December 6, 2022

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Svante Papu: Nobel Prize for Human Evolution

October 3 was an important day not only for molecular anthropology but for all studies of human evolution: the 2022 Nobel Prize in Physiology and Medicine was awarded to Svante Papu, the father of ancient DNA research, for his contribution to deciphering the entire genome of Neanderthals and other now-extinct hominins.

The history of human evolution, not only the history of our species but of all other hominins that preceded or accompanied it, has been reconstructed for more than a century only by analyzing the morphological features of fossil remains and artefacts related to the petroglyph. Industry, which has orthopedic, ivory and technical certifications. However, at the beginning of the 1960s, a new discipline developed in the biological field: genetics. From that moment on, anthropology began to revolutionize. However, the real renaissance in anthropological studies did not ripen until thirty years later, in the late 1980s, when in the laboratory of Alan Wilson, at UC Berkeley, the same professor and two of his students, Rebecca Kahn and Mark Stoneking, analyzed mitochondrial DNA (mtDNA). ) to many men and women from different population groups today and determined that our species originated in Africa about 300-200 thousand years ago. This DNA consists of only 16,500 base pairs compared to about 3 billion base pairs; It is present in many copies in our cells while there are only two copies of the nuclear version; It is transmitted only by the mother. These characteristics make mtDNA easy to study but only illustrate our evolutionary history from the maternal side and we will have to wait for the development of new techniques to subject nuclear DNA for analysis and thus define human evolution in more detail.

In those years, young Svante Papu arrived at the laboratory of Wilson, who revolutionized anthropology by using genomics in the analysis of ancient populations. So not only morphology but also DNA to study our history.

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His first attempts on mummified human tissue did not produce good results and to improve the technique he decided to work on samples from a recently extinct animal: the quagga. The results were satisfactory. At that point, Babu decided to devote himself again to the ancient history of hominins and established paleogenomics to investigate the genetic differences between different species.

The DNA molecule begins to degrade, that is, to disintegrate, after the death of individuals and current technology makes it possible to restore extensions of great lengths for study in human discoveries dating back about 400,000 years. Thus the material from which DNA is derived is the structural material.

Neanderthals lived in Europe, the Middle East, and Western Asia about 400,000 to 30,000 years ago, so this mink came to the benefit of Babu. The anthropological problem facing scholars of several generations has been to determine whether we are different species or only subspecies of one species.

The first Neanderthals to whom Papu focused his attention was the one he gave his name: the 1856 fossil found in Feldhofer Cave, in the Neanderthal Valley near Düsseldorf, Germany, for which William King devised a specific name for Homo in 1864. Neanderthals.

Initially, Pääbo looked at mtDNA and had to immediately solve the contamination problem. As it can be understood, the fossils pass through many hands and many DNA molecules of present-day men and women, as well as microorganisms, are deposited. If you’re not careful, the DNA being analyzed is not that extracted from the find but from the person who touched it. For this reason, when possible, the pulp of fossil teeth is the preferred material, since it is contained in a closed “box”, or the internal parts of the skeleton are used, such as petroglyphs, the pyramidal part of the temporal bone where the organs of the internal auditory system are located. In the absence of these sections, fragments of compact bone are used. The laboratories in which analyzes are performed are regulated according to internationally established procedures.

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It must be remembered that studies to reconstruct the nuclear genome of our species began in the 1990s and the first results of this human genome project were revealed in 2001. In the same years, Pääbo began obtaining some of the first short sequences of Neanderthal mtDNA, the longest of which, 379 nucleotides Specifically, it has been compared to a current human, proving that it is completely alien to our own vagaries. Papo’s conclusion was that we and Neanderthals were two different species that never crossed each other and that we shared a common ancestor about 690-550,000 years ago.

Of course, the result of the study had to be verified by increasing the number of mtDNA nucleotides in the sequence and the number of fossils from different parts of the species range. In 2008, Pääbo published the entire neanderthal mtDNA sequence and the results were identical: showing the difference between their line and ours going back about 660,000 years.

But when Papo switched to nuclear DNA, the picture changed. The first results dated back to 2010 and showed that there was between 1 and 2 percent of Neanderthal DNA in our genome. Not in all populations, however. There was no trace of Neanderthal genes in Africans, meaning that the crosses occurred after the first Homo sapiens emerged from the African cradle, about 70,000 years ago. And the place where they met is certainly the Middle East. Currently, a very modest trace of Neanderthal DNA is also found in some African groups: about 0.3%, due to current human migrations to Africa that previously mixed with Neanderthals.

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Today we know that all kinds of animals, including ourselves, are not airtight boxes. So some simple crossover is possible and documented.

Also in 2010, Pääbo achieved another unusual result: the first molecular identification of a fossil species. Until then, in order to identify a new species, it was necessary to have fossil remains that could be compared with known species from other species. In 2008, a battalion of young hominins who lived between 48 and 30 thousand years came to light in the Denisova Cave in the Altai Mountains in Russia. Morphologically, attribution was not possible, but a study of mtDNA allowed Pääbo to discover that this DNA was different from both Neanderthals and Neanderthals. So it was a new type of hominin: Denisova. The common ancestor of Denisovans, Neanderthals and us lived about a million years ago: nearly twice the relative history of the common ancestor of Neanderthals and us.

The study of DNA then showed that the divergence between Denisovans and Neanderthals could go back to about 470-380 thousand years ago, while that between them and us would go back to about 760-550 thousand years ago. And again, there was gene flow between Neanderthals and Denisovans and between the latter and the only current population of Melanesia.

Pääbo’s position for ancient genome research is still open within the Darwinian theory of evolution and certainly in the near future this discipline, and more generally studies of ancient macromolecules, will play a greater role in defining the framework of human evolution in detail, which proves this. Be very complex, and to illustrate some passages from our past that are still mysterious.