In 2010, the revelation that early humans and Neanderthals interbred was groundbreaking, revealing a biological tradition affecting present individuals’ circadian rhythms, defense systems, and pain perception. However, understanding the gene flow in the opposite direction has been challenging. A new study, which was published in the journal Science on July 12, clarifies how this intertwining affected Neanderthals, implying multiple DNA exchanges over the course of 250, 000 years, reversing the Homo sapiens ‘ migration out of Africa, according to CNN.
Most genetic data indicates that modern humans evolved in Africa 250, 000 years ago, remained there for 200, 000 years, and then dispersed globally around 50, 000 years ago. ” To date, most genetic data suggests that modern humans evolved in Africa 250, 000 years ago, stayed put for the next 200, 000 years, and then decided to disperse out of Africa 50, 000 years ago and go on to people the rest of the world”, said Joshua Akey, a professor at the Lewis-Sigler Institute at Princeton University and the study’s senior author.
” Geography is essentially blind to anything that does n’t leave ancestry to contemporary populations,” said the professor. What I find to be “kind of cool” about this ( paper ) is that it offers genetic data on these African dispersals that we previously could n’t see,” Akey continued.
The research indicates that since the introduction of Homo sapiens between 250 and 300,000 years ago, Neanderthals and other archaic people, including Denisovans, were more frequent than previously thought. Scientists can reconstruct relationships between populations or species by comparing DNA sequences in databases and estimating the duration of DNA exchanges.
The study found that humans left Africa and interbred with Neanderthals in three waves: the first between 200, 000 to 250, 000 years ago, shortly after the first Homo sapiens fossils appeared in Africa, the second around 100, 000 years ago, and the third between 50, 000 to 60, 000 years ago. The most recent incident from 50 000 years ago was already well known and was first discovered in 2010 when the first Neanderthal genome was sequenced.
The study found that Homo sapiens’ DNA contributed to Neanderthals in earlier generations, accounting for 10 % of the Neanderthal genome over the course of 200 000 years and reducing in proportionately 2.5 % to 3.7 %. Unassociated from the study, Lauriets Skov, a geneticist and postdoctoral researcher at the University of California, noted that a comparable study last year demonstrated a genetic exchange 250, 000 years ago. However, the contribution around 100, 000 years ago was a new finding.
However, it seems as though human and Neanderthal history are much more connected than previously believed, Skov wrote in an email.
During the earlier waves of interbreeding, Neanderthals incorporated human genes, and their offspring remained within Neanderthal groups. These early mating episodes were the result of a few pioneering Homo sapiens leaving Africa and establishing strong populations elsewhere. In contrast, their genetic impact on contemporary human populations was significant, but it had a significant impact on the Neanderthal genome.
Akey noted that population differences could explain why Neanderthals did n’t initially have a large genetic record left by early Homo sapiens. According to Akey,” I believe the simplest explanation is that this reflects changes in population sizes over time.” ” At first, ( early ) modern humans were emigrating from Africa, and Neanderthal populations were large enough to essentially withstand these initial influxes of humans and their genes into the Neanderthal population.”
When Homo sapiens left Africa around 60, 000 years ago in a more substantial migration, the offspring of Homo sapiens-Neanderthal encounters remained within modern human populations, thus influencing our gene pool today. Using machine learning, the research team decoded and sequenced genomes from three Neanderthals dating back 50, 000 to 80, 000 years, found in Croatia and the Altai Mountains. They compared this data with the genomes of 2, 000 present-day humans.
We created a framework to determine whether there was a human-Neanderthal gene flow, determine how many Neanderthal genomes contained modern human sequence, and identify the specific Neanderthal genome regions that contained modern human sequences, according to Akey.
The population dynamics that were discovered may contribute to the disappearance of Neanderthals thousands of years ago, according to researchers. According to the analysis, the Neanderthal population was 20 % smaller than initially thought. Akey added,” Human populations were larger, and like waves crashing on the beach, eventually eroded the Neanderthals”, implying Neanderthal genes were likely absorbed into the human population during the last wave of interbreeding.
Although I do n’t believe it’s the only explanation, I believe the incorporation of Neanderthals into human populations likely accounts for a large portion of the reason the Neanderthals disappeared, he said.
Chris Stringer, research lead in human evolution at the Natural History Museum in London, agreed. He claimed that the final interbreeding stage, which reduced Neanderthal diversity as their DNA entered the larger human gene pool, may have contributed to the Neanderthal extinction. Stringer emphasized,” I think that is an important point. Further evidence that the late Neanderthals may have been an endangered species even without competition from an expanding Homo sapiens population is that is being affected by the increase in Neanderthal genetic diversity from interbreeding with sapiens.
There are some Homo sapiens fossils, like those found in Greece and Israel, that may reflect these early, less successful migrations out of Africa. These fossils often show traits considered primitive, such as larger brows and variable chins, possibly due to gene flow from Neanderthals.
” I’ve interpreted ( these ) traits ( as ) retained from more primitive non-Neanderthal ancestors, but they could alternatively be signs of gene flow from Neanderthals, and perhaps such characteristics should be looked at again now, in the light of this new work”, Stringer said.
