Ancient DNA, article by Pere Puigdomènech

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

Those of us who work in the field of molecular biology remember Svante Pääbo’s 1985 paper in which he analyzed Egyptian mummy DNA. It seemed like an impossible milestone and many of us felt that he had been very lucky but that it would be difficult to repeat. DNA is certainly a very stable molecule. But dead biological tissue is subjected to the action of many organisms that decompose it and break 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 studying it, masks the result. Pääbo solved these problems and studied older and older samples.

New technologies, on the one hand, are finding ways to prevent sample contamination and efficiently extract small DNA fragments. On the other hand, DNA amplification methods such as PCR and DNA sequencing methods are used, which are done on small fragments and small samples. Their work was also favored by the fact that they gradually became available increasingly rich information about the genomes of different speciesand among them the human, which can be analyzed using more efficient bioinformatics methods.

All of these new methods and a great deal of rigor and persistence are driving us further and further back in time to be able to study DNA and to do so with ever scarcer samples. One of the most surprising results of Pääbo’s work is 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 neanderthal genome from bone samples found in various places in Europe. Even more surprising, 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 for Neanderthals. a separate species that we now call Denisovans. When the DNA of Neanderthals and Denisovans was compared to that of humans, fragments of their genomes appeared in the genomes of European or Asian populations, indicating that these species and ours co-existed and were related frequently enough.

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Ancient DNA research techniques 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 the remains of other species. There are currently studies to find out what ancient populations ate study of plant or animal remains from the caves where they lived or scratchy kitchen utensils. In this way, we can know what the populations were like that lived in different parts of the world at different times, what they ate, and how they transformed the species they lived with.

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

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