Where we come from and what makes us human are two of the big questions in science. Swedish biologist and geneticist Svante Pääbo (Stockholm, 1955) has been recognized this year with the Medicine Nobel Prize for their impressive contributions to answering those questions. In 2010, the researcher succeeded in sequencing the neanderthal genome, an extinct relative of modern humans. In addition, he is the discoverer of another previously unknown hominid, that of denisova. His studies allowed him to conclude that modern humans carry genes from these two ancient species, with whom we were related after migrating out of Africa about 70,000 years ago. They still influence us. For example, in the way our immune system reacts to infections.
Pääbo’s work, recognized by the jury at Sweden’s Karolinska Institute as “transcendental”, gave rise to an entirely new scientific discipline: paleogenomics. In 2018, she received the Princess of Asturias award for it.
Early in his career, the researcher was fascinated by the possibility of using modern genetic methods to study Neanderthal DNA. However, he soon realized the extreme technical challenges involved, because after thousands of years DNA is highly degraded, fragmented and contaminated.
He began to develop more refined methods. His efforts paid off in the 1990s, when Pääbo succeeded in sequencing a region of mitochondrial DNA from a 40,000-year-old bone. For the first time, we had access to a sequence from an extinct relative. Comparisons with contemporary humans and chimpanzees showed that Neanderthals were genetically distinct.
Established at a Max Planck Institute in Leipzig, Germany, Pääbo and his team went much further. In 2010 they achieved the seemingly impossible by publishing the first Neanderthal genome sequence. Comparative analyzes showed that Neanderthal DNA sequences were more similar to sequences from contemporary humans originating in Europe or Asia than to Africans. This means that Neanderthals and Sapiens interbred during their millennia of coexistence outside of the mother continent. In modern humans of European or Asian descent, approximately 1-4% of the genome is Neanderthal.
In 2008, a 40,000-year-old finger bone fragment was discovered in Denisova Cave in the southern part of Siberia. The bone contained exceptionally well-preserved DNA, which Pääbo’s team sequenced. The results caused a sensation: it was a previously unknown hominid, which was given the name Denisovan. Comparisons with sequences from contemporary humans from different parts of the world showed that both species also interbred. This relationship was first observed in populations from Melanesia and other parts of Southeast Asia, where individuals carry up to 6% Denisovan DNA.
Thanks to Svante Pääbo’s discoveries, we now understand that archaic gene sequences from our extinct relatives influence the physiology of modern humans. An example of this is the Denisovan version of the EPAS1 gene, which confers a survival advantage at high altitude and is common among modern Tibetans. Other examples are Neanderthal genes that affect our immune response to different types of infections, including Covid-19.
But, above all, Pääbo’s discoveries help us understand who we are, what distinguishes us from other human species and what makes ours the only one on the face of the Earth. Neanderthals, like Sapiens, lived in groups, had large brains, used tools, buried their dead, cooked and adorned their bodies.
They even created cave art, as evidenced by paintings from at least 64,000 years ago discovered in three Spanish caves: La Pasiega in Cantabria, Maltravieso in Cáceres and Ardales in Málaga. They were similar to us but they had genetic differences that Pääbo brought to light and that may explain what made them disappear and we are still here.