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The 2022 Nobel Prize in Physiology or Medicine will be awarded to Svante Pääbo for his discoveries concerning the genomes of extinct hominins (the group consisting of modern humans, extinct human species, and all our immediate ancestors) and human evolution, as per the decision of the Nobel Assembly at Karolinska Institutet. Besides discovering a previously unknown hominin, Denisova, his pioneering research also succeeded in sequencing the genome of the Neanderthal, an extinct relative of ours. He found that gene transfer had occurred from these now extinct hominins to Homo sapiens 70,000 years ago, following the migration out of Africa. His research gave rise to a new scientific discipline, paleogenomics, and his discoveries allow scientists to explore what makes us uniquely human by revealing genetic differences distinguishing all living humans from extinct hominins.
Research shows that Homo sapiens first appeared in Africa some 300,000 years ago, while Neanderthals populated Europe and western Asia from about 400,000 years until 30,000 years ago, before becoming extinct. Groups of Homo sapiens migrated from Africa to the Middle East about 70,000 years ago, spreading then to the rest of the world. Thus, Homo sapiens and Neanderthals coexisted in parts of Eurasia for tens of thousands of years, and scientists have always been intrigued about the relationship between the two.
Almost the entire human genome had been sequenced by the late 1990s, which allowed studies of the genetic relationship between different human populations. Svante Pääbo was interested in utilizing modern genetic methods to study the DNA of Neanderthals, but faced extreme technical challenges, since DNA becomes chemically modified and degrades into short fragments with the passage of time, and additionally, what remains is contaminated with DNA from bacteria and contemporary humans. He started to develop methods to study DNA from Neanderthals and decided to analyze DNA from Neanderthal mitochondria. Using refined methods, he succeeded in sequencing a region of mitochondrial DNA from a 40,000-year-old bone fragment, and comparisons with contemporary humans and chimpanzees showed that Neanderthals were genetically distinct.
Pääbo then decided to sequence the Neanderthal nuclear genome. Engaging with some critical experts on population genetics and advanced sequence analyses, he was successful in achieving his goal, publishing the first Neanderthal genome sequence in 2010. Comparative analyses showed that the latest common ancestor of Neanderthals and Homo sapiens lived around 800,000 years ago. He and his colleagues began investigating the relationship between Neanderthals and present-day humans from different parts of the world. They found more similarity of DNA sequences between Neanderthals and contemporary humans originating from Europe or Asia than to contemporary humans originating from Africa. Neanderthals and Homo sapiens interbred during their long period of coexistence, and in modern day humans with European or Asian descent, about 1-4% of the genome originate from the Neanderthals.
In 2008, a 40,000-year-old finger bone fragment was discovered in the Denisova cave in Siberia that had exceptionally well-preserved DNA, which Pääbo and his team sequenced. The results showed that the DNA sequence was unique, as compared to sequences from Neanderthals and present-day humans. This was a new discovery of an unknown hominin, which they named Denisova, and when it was compared with sequences from contemporary humans, it showed that there had also been gene flow between Denisova and Homo sapiens. They found that individuals carry up to 6% Denisova DNA in Melanesia and other parts of South East Asia.
Pääbo’s discoveries show that, at the time of Homo sapiens’s migration out of Africa, at least two extinct hominin populations inhabited Eurasia, with Neanderthals living in western Eurasia and Denisovans in the eastern parts of the continent, and during the Homo sapiens’ migration outside Africa, they encountered and interbred with both Neanderthals and Denisovans.
Svante Pääbo was born in Stockholm in 1955. He became Professor at the University of Munich, Germany in 1990, and in 1999 he founded the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. He is also an adjunct Professor at Okinawa Institute of Science and Technology, Japan. He established a new scientific discipline called paleogenomics, which helps to identify genetic differences between Homo sapiens and our extinct relatives.
