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In 2010, scientists reported the discovery that Neanderthals had interbred with Homo sapiens, or modern humans in the anatomical sense. Later, researchers revealed the role of genes in modern humans, including effects on circadian rhythms, immune system function, and pain sensitivity.
So, did Homo sapiens' genes also influence Neanderthals? How did the fusion of the two populations shape the Ni people? Did they drive the process of their extinction?
These are difficult questions to answer, but with the help of new technologies, researchers are painting a clearer picture. A new study recently published in the journal Science shows that Homo sapiens and Homo nindiensis groups have exchanged DNA at multiple points in time over the past 250,000 years – providing a wealth of information to reconstruct the process of Homo ni's disappearance, and potentially rewriting the story of when and how Homo sapiens left Africa.
Jo·shua Akey, a professor of ecology and evolutionary biology at Princeton University and one of the paper's authors, notes that most genetic data to date suggest that our ancestors evolved on the continent 250,000 years ago, lived for another 200,000 years, and eventually migrated out of Africa and to other parts of the world 50,000 years ago.
"But at this stage of genetics, it is difficult to trace a group that is not our ancestor. I think one of the interesting things about this paper is that it gives us a genetic glimpse into a journey out of Africa that we didn't know about in the past. Modern human ancestors may have interacted with Neanderthals and other hominins, including Denisovans, much more frequently than previously thought. ”
In the Neanderthal Museum in Krapina, Croatia, a work of art depicting the cave life of a Neanderthal family is on display
Three large hybrids
By comparing DNA sequences in databases, scientists can reconstruct relationships between different populations or species, and because the rate at which genetic changes occur is stable within a generation, geneticists can calculate the timing of the exchange of DNA between two populations.
According to the existing results, the process of meeting and interbreeding with Neanderthals after Homo sapiens left Africa was divided into three waves: the first wave was about 200,000 to 250,000 years ago, shortly after the appearance of the oldest known Homo sapiens bones on the African continent; The second wave occurred 100,000 years ago; The last time was about 50,000 to 60,000 years ago.
The last wave of migration has been widely recognized by the academic community and was first confirmed in 2010, when the 2022 Nobel laureate evolutionary geneticist S·vante Pääbo sequenced the first Ni genome. But the latest Science paper shows that the first two waves of migration are markedly different from the last one – the latter – a truly mass migration that eventually led to the spread of modern humans across the globe.
According to the authors, more than 200,000 years ago, the proportion of Homo sapiens DNA in the Neanderthal genome may have been as high as 10 percent, and then gradually decreased over time, on average, at the level of 2.5 to 3.7 percent.
Genetic Detective
During the first two waves of migration and hybridization, Neanderthals absorbed Homo sapiens genes, and the hybrid offspring remained in the Neanderthal population.
In Professor Eikey's words, these early hybridization events were the result of a small group of pioneer Homo sapiens leaving Africa without gaining a foothold outside the country, leaving little record in the gene pool of modern humans, but having a significant impact on the Ni genome.
"I think the simplest explanation is that it's a reflection of how the size of the population has changed over time. At first, Homo sapiens came out of Africa and encountered a fairly large population of Homo sapiens, who absorbed relatively scattered Homo sapiens genes. But when Homo sapiens left Africa about 60,000 years ago and continued to attack the rest of the world, the hybrid descendants of Homo sapiens and Homo nindiens grew up in the former population, and the Neoni bloodline was integrated into the modern human gene pool and influenced our lives today. ”
In the new study, Professor Eggy's team used machine learning to decode and sequence the genomes of three Neanderthal fossils. The fossils date from 50,000 to 80,000 years ago and were excavated in three different locations: Vindija caves in Croatia, Denisova caves and Chagyrskaya caves in the Altai Mountains. The researchers also compared the genomic data with the genomes of 2,000 modern humans.
"We have developed a framework to determine whether gene flow between Homo sapiens and Homo nunes is occurring, to estimate how many Homo sapiens sequences are in the Ni genome, and even to determine where those Homo sapiens sequences are located," Ekie said. ”
Russia archaeologists are excavating inside the Denisova cave in the Altai Mountains
The mystery of the disappearance of Neanderthals
Chris Stringer, a physical anthropo·logist who leads the study of human evolution at the Museum of Natural History in London (not involved in the new study), said that the small number of Homo sapiens fossils appears to reflect the species' less successful migration history in its early stages, leaving Africa for what is now the Middle East and Europe.
This part of the remains includes 210,000-year-old Homo sapiens fossils found in the caves of Apidima in southern Greece, as well as remains found at the Skhūl and Qafzeh sites in Israel. Israel's fossils have "primitive features" such as thicker brow bones, flatter skulls, and diverse mandibles.
Stringer suggests that these traits appear to have been inherited from more primitive Henneanderthal ancestors, and may also reflect gene flow between Homo neandeines and human species. It may be time for scholars to re-examine these characteristics of the Ni people in the light of new discoveries. ”
A skull excavated at the Kafze site in Israel is believed to belong to Homo sapiens
Eggy et al. believe that their new findings on population dynamics may be the main reason for the disappearance of this close relative 40,000 years ago. In addition, new research suggests that the population size of the Ni people at that time was 20 percent smaller than previously thought.
"Homo sapiens is much larger. They eventually eroded Neanderthals like waves crashing against sand. It is likely that the gene pool of Homo nindiens was absorbed during the last wave of migratory hybridization of Homo sapiens, that is, 50,000~60,000 years ago. Extinction is a complex issue, and there should not be only one explanation...... But I believe that the absorption of Homo sapiens genes by the Homo sapiens population is likely to be a large part of the reason for the extinction of the former. ”
Stringer agrees with Ekie et al.'s theory that as Homo sapiens DNA enters the larger Homo sapiens gene pool, the former population becomes smaller and less diverse.
I think that's critical. If the increased genetic diversity of Neanderthals by hybridization with Homo sapiens were not taken into account, their effective population size would have been greatly reduced, further evidence that Homo sapiens may have been on the verge of extinction even without the competition of expanding Homo sapiens populations. ”
Sources:
How did Neanderthals disappear? New DNA analysis sheds light on the mystery
END
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