Princeton geneticists led by Joshua Akey have discovered multiple waves of interbreeding between modern humans, Neanderthals, and Denisovans over 200,000 years. Utilizing advanced genetic tools, they mapped gene flow - showing that these ancient groups interacted more than previously believed. Neanderthals may not have gone extinct but instead interbred into modern populations through interbreeding rather than becoming extinct altogether.
(Image Source: Princeton University)
Princeton University Genetics Research: Under Professor Joshua Akey's leadership, geneticists from Princeton University are conducting groundbreaking genetic research. Recent discoveries show that our ancestors had far more contact with Neanderthals and Denisovans than was thought previously, providing new insight into how these ancient populations lived, interacted, and ultimately vanished over time.
Neanderthals have long been seen as distant relatives of modern humans. Still, Akey's team has discovered something surprising - for approximately 200,000 years, modern humans and Neanderthals coexisted, regularly exchanging genetic material and intermingling with one another.
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Although the idea that modern humans and Neanderthals interacted is not new, their scale and timing were shocking. According to Liming Li from the Southeast University of China, who worked in Akey's lab, geneticists have identified multiple waves of human-Neanderthal interbreeding.
Modern humans split from the Neanderthal family tree approximately 600,000 years ago and began developing distinct physical features about 250,000 years ago. But modern humans did not live completely apart from Neanderthals: Akey's research indicates that between when modern humans first appeared and when Neanderthals eventually went extinct around 30,000 years ago, both groups maintained regular contact.
"Now we understand that, for most of human history, modern humans and Neanderthals interacted frequently," Akey stated. This discovery counters earlier thinking that modern humans originated in Africa around 200,000 years ago before leaving to disperse across the globe about 50,000 years later.
Akey and her team reached their conclusions after conducting an exhaustive analysis of over 2,000 living humans as well as genetic data from three Neanderthals and one Denisovan. With IBDmix - an advanced machine learning tool used to decode genomes - they tracked gene flow between different hominin groups over 250,000 years.
Scientists had traditionally studied ancient human genetics by comparing modern genomes with those from "reference populations", or groups thought to contain little Neanderthal or Denisovan DNA. However, Akey's research demonstrated that even these reference groups contained small amounts of Neanderthal genetic material that was likely introduced to the South by ancient travellers.
IBDmix revealed three waves of contact between modern humans and Neanderthals; the first occurred 200,000 to 250,000 years ago, followed by 100,000-120,000 years ago and, ultimately, around 50,000-60 years ago - suggesting early humans and Neanderthals interacted more frequently than had been anticipated. This evidence shows how early humans interacted more often than previously believed.
Akey's research paints an image of our ancestors as being constantly on the move - travelling between Africa and out, mixing with different hominin populations along the way.
"Humans have been migrating more widely and encountering Neanderthals and Denisovans than previously acknowledged," asserted Akey, underscoring the significance of interaction over isolation in human evolution. This new perspective on early human migration emphasizes dispersal rather than isolation for shaping its history.
One of the most remarkable findings from Akey's work is his realization that early humans contributed their DNA to Neanderthals, while Neanderthals left theirs behind on us. Liming Li and Joshua Akey reversed the usual focus of genetic research by searching for evidence of modern human DNA within Neanderthal genomes.
Researchers discovered that offspring from early human-Neanderthal unions often remained within Neanderthal communities, leaving no genetic signature among living humans today. By studying Neanderthal DNA, the team discovered evidence of early migrations which had gone undetected previously.
Another significant discovery was that Neanderthal populations were much smaller than had been believed. Genetic modelling has long relied upon diversity - or genetic variety within a population - as an indicator of size; more diverse populations often become larger. However, Akey's research demonstrated that some of this diversity attributed to Neanderthals may actually come from interbreeding between Neanderthals and early humans.
Due to these findings, estimates for the size of Neanderthal populations were revised downward from 3,400 breeding individuals to just 2,400, making these primitive humans even more vulnerable to extinction.
Though Neanderthals disappeared from historical records around 30,000 years ago, Akey is reluctant to use the term "extinct." He believes they were mostly integrated into modern human populations through interbreeding rather than entirely disappearing from history.
Fred Smith first put forward this concept of assimilation back in 1989, while Akey's research offers strong genetic support to this hypothesis.
"Neanderthals teetered on the brink of extinction for many generations," Akey noted. A combination of factors likely sealed their demise: small population size and interbreeding with modern humans likely resulted in their demise. Modern humans were like waves crashing on a beach, eroding Neanderthal populations gradually until they were completely integrated into our ancestors' communities.
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Akey and his team's research provides a fresh view of human evolution, one that emphasizes ancient humans' interdependency. Neanderthals, Denisovans and early modern humans weren't isolated species living separate lives - rather, they interacted and exchanged genetic material in complex webs that changed history over time.
As Akey and his colleagues continue their studies of ancient hominin genetic relationships, they are uncovering new chapters in humanity's story - reminding us that our shared history is far more complicated and intertwined than we ever realized. Follow Education Post News for more updates.
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