The origin of humanity can be summed up as a long history of hybridization and migration. The more data we have on the prehistory of our species, thanks in particular to the genetic revolution led by Nobel Prize winner Svante Pääbo, the more complex and, at the same time, simpler the picture becomes: over the millennia, the different species of Homo— to which we ourselves belong — populated the Earth in successive waves from Africa, some successfully, others doomed to extinction. The study of fossil DNA has also shown that different species interbred during this journey and that these genetic exchanges have allowed us to discover the only humans who populate the Earth today: A wise manWe.
The latest news on Neanderthals and Denisovans — the two archaic human species closest to ours, which went extinct about 40,000 years ago, although many sapiens still carry their genes — have only confirmed this long journey, geographical, but also genetic.
It all started when Swedish scientist Svante Pääbo had the intuition that it was possible to extract and analyze the DNA of species that had disappeared thousands of years ago. As is often the case with scientific breakthroughs, he had to work alone at first, secretly performing genetic analyses on mummies. It is worth remembering that no one believed – or funded – Hungarian researcher Katalin Karikó when she decided to study messenger RNA, a discovery that earned her the Nobel Prize and, just as importantly, helped stop the Covid-19 pandemic.
By sequencing the Neanderthal genome, Pääbo’s team at the Max Planck Institute for Evolutionary Anthropology discovered in 2010 that modern non-African humans share about 3% of genes with this extinct human species. And by analyzing scattered, small bone remains found in a Siberian cave, he discovered another human species closely related to Neanderthals, named after the cave where they were found: the Denisovans. It also allowed him to identify the first known hybrid hominid in history, Denisova 11, aka Denisdied 50,000 years ago at the age of 13, whose mother was Neanderthal and father Denisovan. The fact that a hybrid hominid appeared among the rare remains found of this species shows how constant the exchanges must have been.
For most researchers—some still deny the Denisovans the status of distinct species—Neanderthals lived in Europe and Denisovans in Asia. Both species either disappeared with the arrival of Homo sapiens or, as is increasingly evident, were absorbed by the new humans. To some extent, we are also them. Science recently published magazine The result of an analysis of three complete Neanderthal genomes: They did not die out, but were assimilated. Eventually, successive waves of Homo sapiens immigration from Africa overwhelmed the Neanderthals until they could no longer remain a distinct species and were eventually assimilated by sapiens genetics, summarizes geneticist Joshua Akey, co-author of the study.
The last Neanderthals were a group of about 2,500 individuals lost in the vastness of prehistoric Europe. Their solitude also represents the history of humanity, which has become multiple: at one point, 200,000 years ago, up to eight different human species coexisted on Earth. Only us remain, the humans that the French paleoanthropologist Jean-Jacques Hublin defines as “the solitary species”.
Information on the Denisovans, as well as on their remains, is much scarcer, although a fascinating map of the evolution – and disappearance – of this species is gradually emerging. In early July, Science The researchers published the discovery of a Denisovan rib dating back about 40,000 years, the youngest remains discovered so far (by which time Homo sapiens had colonized Australia from Africa and reached Europe). “This is extremely recent,” Bence Viola, a paleoanthropologist at the University of Toronto who was not involved in the research, said in the Science paper. “This date puts the Denisovans well within the period of modern human history in the (broader) region.”
Researchers Silvana Condemi and François Savatier have just published the book The Denisova Enigma (The Denisovan Enigma, not yet translated from French), which compiles all the known data on these humans, whose genetic heritage is found in populations from places as remote as Australia or the Bataan Peninsula in the Philippines. Thanks to their genes, they have helped modern humans survive in high places like Tibet, or confront pathogens in tropical forests, such as in the Philippines.
This is how the authors describe, for example, what happened over the millennia in Denisova Cave in the Altai Mountains, a place where cultures have crossed paths since the dawn of time: “The general panorama of human life in Denisova is now clear: for tens of thousands of years, during the interglacial period, Neanderthals and Denisovans – two human species closer to each other than to Homo sapiens – frequented the cave and met there. Some researchers even believe that these two species could have founded a common culture in Altai.”
The vision of this cave where different species coexisted is perhaps too idyllic: in many other sites, such as the Cueva del Castillo in Cantabria, in northern Spain, there are traces of the occupation of Neanderthals and Homo sapiens, but not simultaneously. When one of the groups arrived, the other had already disappeared. However, genetic exchanges are indisputable – even if they seemed impossible only twenty years ago – and it is now certain that the genes of Neanderthals and Denisovans helped modern humanity to adapt and survive. But it is also clear that they no longer exist – even if we have inherited their DNA – and that Homo sapiens is the only species that populates the Earth. Our arrival meant their extinction, but not without them first mixing. The origin of humanity revealed by the paleogenetic revolution has become a story of migrations and mixtures. And this, without a doubt, offers many readings for our intolerant present.
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