Svante Pääbo: DNA Hunter

We have known for a few centuries now that modern humans – or us Homo sapiens – weren’t the only human species to have existed on earth. But we’ve been inclined to view our species as one belonging to a special and distinctive category. And the others as something almost subhuman – a far removed, and not particularly bright, cousin.

And how could you fault this view? We made it; they didn’t.

Swedish geneticist Svante Pääbo – whose work in the field of ancient DNA studies has won him the Nobel Prize in Physiology or Medicine – showed just how wrong we’ve been all this while. Forget the dumb Neanderthal jokes, Pääbo showed that Homo sapiens and Neanderthals mated all the time. So much so that many of us – especially those living in Europe and Asia today – owe anywhere from one to four percent of our genomic heritage to these archaic species.

This is just one of the many things we have come to learn from his work. A pioneer in this new field of ancient DNA research, Pääbo developed new methods of dealing with ancient DNA, sequenced the Neanderthal genome, discovered another previously unknown species, the Denisova, and also showed us how the gene flow between our ancestors and archaic species impacts us today. Two years ago, for instance, he showed that the Neanderthal genes we carry can affect our immune response to different types of infections when he found that Covid-19 caused more severe symptoms in people who had inherited a stretch of Neanderthal DNA. Before that, he found that present-day Tibetans, whose ancestors had interbred with Denisovans, carry a very specific Denisovan version of a gene (EPAS1) that helps them live in the extreme low oxygen environment of the Tibetan plateau.

Pääbo wasn’t always working in this field of paleogenomics. The child of a secret affair between an Estonian chemist Karin Pääbo (his mother) and the Swedish biochemist Sune Bergström, who incidentally won the 1982 Nobel prize for discovering postaglandins, Pääbo began his career working with researchers who studied DNA to understand its relationship to disease. No one had considered extracting and studying DNA from ancient tissue in the early 1980s. And Pääbo’s earliest experiments involved buying a piece of liver, secretly heating it in a lab oven for several days, and then retrieving just enough DNA from it to give him the confidence that he could take this forensic approach to studies about our ancient past too.

Pääbo tried to extract and study genetic material from mummies, before switching to even older genetic material – those of extinct hominins. But that’s more easier said than done. DNA begins to decay the moment an organism dies. And the trace amounts left behind after thousands of years is often contaminated with other DNA. Trying to put these tiny traces of damaged DNA is so complex it is like, in the words of the New Yorker writer Elizabeth Kolbert, reassembling ‘a Manhattan telephone book from pages that have been put through a shredder, mixed with yesterday’s trash, and left to rot in a landfill’.

Pääbo spent decades developing new and efficient methods of handling such ancient genetic material, while also benefitting from the leaps the technology in DNA sequencing was undergoing. He first made a splash in the late 1990s when he sequenced a region of mitochondrial DNA from a 40,000 year old Neanderthal fossil. This was the first time we had access to a genetic sequence from an extinct relative. By 2010, he had achieved the seemingly impossible, when he published the first Neanderthal genome sequence. Around this time, he also discovered a hitherto unknown species, the Denisovans, from the fragment from a 40,000-year-old finger bone in a Siberian cave. From his work, we now know that after Homo sapiens migrated out of Africa, they encountered Neanderthals living in western Eurasia and Denisovans in the eastern parts of the continent and interbred with them.

We still do not know much about this prehistoric period, or all the ways in which our genetic heritage from diverse archaic species impacts us today. But by taking this new science of DNA studies to our ancient past, Pääbo has been able to ask the kind of profound questions so far only reserved to poets and philosophers: Who are we? Where do we come from? And what makes us human?

DNAHomo sapiensmedicineNeanderthalsNobel PrizeSvante Pääbo