Ancient DNA, article by Pere Puigdomènech

This year’s Nobel Prize in Physiology and Medicine has been awarded to Swedish-born researcher Svante Pääbo, for his discoveries analyzing DNA from ancient samples. Pääbo’s influence in this field is indisputable. The methods he has helped develop have revolutionized entire fields of ancient history research and in the evolution of the human species.

Those of us who are working in Molecular Biology remember the article by Svante Pääbo from 1985 in which he analyzed the DNA of an Egyptian mummy. It seemed like an impossible milestone and many of us thought that he had been very lucky, but that it would be difficult to repeat it. DNA is certainly a very stable molecule. But a dead biological tissue is subjected to the action of many organisms that degrade it and shred the DNA into very small fragments. The DNA in the tissue of a mummy is in very small proportions and any contamination, for example from the DNA of the same researchers who study it, masks the result. Pääbo was solving these problems and was studying increasingly older samples.

New technologies, on the one hand, were finding ways to prevent samples from becoming contaminated and to extract small DNA fragments efficiently. On the other hand, methods are used to amplify DNA, such as PCR, and methods to obtain the DNA sequence, which are done on small fragments and tiny samples. His work was also favored by the fact that he was getting increasingly rich information on genomes of different speciesand among them the human, which can be analyzed using more efficient bioinformatics methods.

All these new methods, and a great deal of rigor and tenacity, have made us go further and further back in the time in which we can study DNA and that we do it with increasingly meager samples. One of the most surprising results of Pääbo’s work has been obtaining the sequence of the genomes of species related to the human species. We are talking about remains that are not 3,000 or 4,000 years old, like the Egyptian mummies, but 40,000 or 50,000 years old. In 2010, Pääbo published the neanderthal genome from bone samples found in different places in Europe. Even more surprising was that, using traces of DNA extracted from the tissues of a hand bone found in a cave in Siberia, they discovered that it was a genome that resembled that of Neanderthals but was different enough to be considered Neanderthals. a distinct species, which we now call the Denisovans. When the DNA of Neanderthals and Denisovans is compared with that of humans, fragments of their genomes appear in the genome of European or Asian populations, indicating that these species and ours have coexisted and have been related frequently enough.

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Techniques for studying ancient DNA have gone back in time. For example, in 2016 Paabo’s group analyzed hominin samples from Atapuerca over 400,000 years old. And they are also used to study remains of other species. Currently, there are studies to find out what ancient populations ate studying plant or animal remains from the caves where they lived or scratching kitchen utensils. In this way we can know what the populations that lived in different parts of the world were like at different times, what they fed on and how they transformed the species with which they lived.

The methods that Pääbo and his team started and have been developing have been applied by other groups and in particular some from here, who have collaborated with him or have applied his recipes. Now it is no longer too surprising that, in excavations looking for remains from ancient times, they collaborate molecular biologists or bioinformaticians and that their results complement site observations or historical data. Those who, like Svante Pääbo, have developed methods to study the DNA of ancient samples have opened a window to study precisely facts about the evolution of our species, of the other species and of our ancient history. He tells us about how our genome has evolved and how some diseases have appeared, which may justify his being awarded the Nobel Prize in Medicine.

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