Nobel Prize in Physiology or Medicine 2022: Swedish geneticist Svante Pääbo, who won the 2022 Nobel Prize in Physiology or Medicine on Monday, did pioneering work in the genetic analysis of Neanderthals and Denisovans, the extinct relatives of human beings or A wise man. Pääbo was awarded the Nobel Prize “for his discoveries concerning the genome of extinct hominins and human evolution”.
His work led to the development of a new branch of science called paleogenomics, or the genetic study of extinct species. Pääbo also discovered a previously unknown hominin, Denisova. Hominins are the extinct ancestors of humans.
Following the migration of A wise man out of Africa around 70,000 years ago, gene transfer occurred from the now extinct hominins to modern humans. The immune system of human beings is able to fight certain infections due to the presence of genes from Neanderthals and Denisovans.
2022 #NobelPrize laureate Svante Pääbo has established an entirely new scientific discipline, paleogenomics. By revealing genetic differences that distinguish all living humans from extinct hominins, his discoveries provide the basis for exploring what makes us uniquely human. pic.twitter.com/AoDNL0zMc7
— The Nobel Prize (@NobelPrize) October 3, 2022
Who were the relatives of modern humans?
Pääbo achieved a seemingly impossible task of sequencing the Neanderthal genome. Neanderthals, the closest extinct human relative, had defining features such as a huge nose, angled cheek bones, sloped forehead, bodies shorter and bulkier than humans, and large brains. The Neanderthal brain was often larger than the human brain, and was proportional to the brawnier bodies of the extinct hominins.
Neanderthals made and used a diverse set of sophisticated tools, controlled fire, lived in shelters, were skilled hunters of large animals, made and wore clothing, and occasionally made ornamental objects.
The first Neanderthal specimen was discovered in 1856 in Germany. In 1864, geologist William King suggested the name homo neanderthalensis for the extinct human relative, making it the first fossil hominin species to be named.
The other archaic human groups who walked the Earth during the middle to late Pleistocene Epoch (one million to 11,700 years ago) were Homo floresiensis and Denisovans.
While Neanderthals developed outside Africa and populated Europe and Western Asia from around 400,000 years until 30,000 years ago, A wise man first appeared in Africa approximately 300,000 years ago. Neanderthals mysteriously disappeared from Earth around 40,000 years ago.
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Some groups of A wise man migrated from Africa to the Middle East about 70,000 years ago. From Africa, these groups spread to the rest of the world. Therefore, for tens of thousands of years, A wise man and Neanderthals coexisted in large parts of Eurasia.
Genetic information about humans as well as Neanderthals is necessary to know about the relationship between the two species. In the early 2000s, about 92 per cent of the genome had been decoded under the Human Genome Project. Earlier this year, the remaining eight per cent was sequenced.
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Pääbo sequenced genome of Neanderthals
Pääbo’s aim was to utilise modern genetic methods to study the DNA of Neanderthals. However, a limitation is that with time, DNA becomes chemically modified and undergoes fragmentation. As a result, only trace amounts of DNA are left after thousands of years. Also, the DNA from archaic specimens is contaminated with the genetic material of bacteria and contemporary humans. In order to overcome these technical challenges, Pääbo, as a postdoctoral student with Allan Wilson, a pioneer in the field of evolutionary biology, started developing techniques to study Neanderthal DNA, the Nobel Prize Organisation says on its website.
DNA is localised in two different compartments in the cell, namely nuclear DNA and mitochondrial DNA. Nuclear DNA, which consists of 300,00,00,000 base pairs, harbours most of the genetic information. Meanwhile, the smaller mitochondrial genome, which contains 16,500 base pairs, is present in thousands of copies. Mitochondria, popularly known as the powerhouse of the cell, is an organelle responsible for energy production. Because it has so many copies, sequencing mitochondrial DNA has a higher chance of success.
In 1990, Pääbo was appointed as a Professor in the University of Munich, where he continued his work on archaic DNA, and analysed DNA from Neanderthal mitochondria.
Pääbo used refined techniques to sequence a region of mitochondrial DNA from a 40,000-year-old piece of bone.
Evidence of interbreeding between humans and Neanderthals
After sequencing the mitochondrial DNA from Neanderthals, Pääbo started sequencing the nuclear genome from the extinct species. At the Max Planck Institute in Leipzig, Germany, Pääbo and his team used modern techniques to sequence the nuclear DNA, and worked with experts on population genetics and advanced sequence analyses.
Pääbo was successful in his efforts, and attained a seemingly impossible achievement. The geneticist published the first Neanderthal genome sequence in 2010. Comparative analyses between Neanderthals and A wise man showed that the most recent common ancestor of the two species roamed Earth around 800,000 years ago.
Through comparative analyses, Pääbo and his team investigated the relationship between Neanderthals and modern-day humans, and found that the DNA sequences were more similar to sequences from contemporary humans originating from Europe or Asia than to contemporary humans originating from Africa. This suggests that Neanderthals and A wise man interbred during their period of coexistence, which lasted thousands of years.
Approximately one to four per cent of the genome of modern-day humans with European or Asian descent has originated from the Neanderthals.
Pääbo discovered an extinct hominin species, Denisova
A 40,000-year-old fragment from a finger bone, discovered in the Denisova cave in the southern part of Siberia, in 2008, contained exceptionally well-preserved DNA. Pääbo and his team sequenced this DNA, and found that the sequence was unique when compared to all known sequences from Neanderthals and present-day humans. A previously unknown hominin had been discovered, which went on to be known as Denisova.
Relationship between Denisovans and modern humans
When the genetic sequences from contemporary humans from different parts of the world were compared, it was observed that gene flow had occurred between Denisova and A wise man. For instance, individuals in Melanesia and South East Asia carry up to six per cent Denisova DNA.
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Why Pääbo’s discoveries are important
Pääbo’s discoveries have provided new insights into the evolutionary history of humans. The geneticist discovered that at least two extinct hominin populations inhabited Eurasia at the time when A wise man migrated out of Africa.
While Denisovans populated the eastern parts of Eurasia, Neanderthals lived in western Africa.
A wise manduring their expansion outside Africa and migration east, interbred with both Neanderthals and Denisovans.
Genomes from extinct hominins in Africa have not yet been sequenced because archaic DNA degrades at an accelerated rate in tropical climates.
Pääbo has established an entirely new scientific discipline called paleogenomics, and along with his team, has analysed several additional genome sequences from extinct hominins.
These sequences constitute a unique resource, which the scientific community can use to better understand human evolution and migration.
With the help of Pääbo’s discoveries, scientists inferred that archaic genetic sequences from our extinct relatives influence the physiology of modern-day humans. The Denisovan version of the gene EPAS1, which confers an advantage of survival at high altitude, is common among present-day Tibetans. Similarly, there are several Neanderthal genes which affect humans’ immune response to different types of infections. Also, his discoveries provide the basis for exploring what makes A wise man uniquely human.
The world is now aware of the genetic differences between A wise man and Neanderthals, thanks to Pääbo’s groundbreaking research.