Neanderthal-Denisovan Ancestor Canoodled With Mystery Group Of "Super-Archaic" Humans

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There could be yet another new character in the story of human evolution – and even more evidence of hanky panky within our evolutionary family.

A new study suggests that the ancestors of Neanderthals and Denisovans, two of Homo sapiens’ closest cousins, interbred with a mysterious population of their own Eurasian predecessors 700,000 years ago, and it's the earliest interbreeding between ancient human populations we know of yet. 

It’s unclear “who” these hominins were, but they are known to be members of a “super-archaic” population that separated from other humans about 2 million years ago. By the researchers' workings, this population was made up of as many as 20,000 to 50,000 individuals.

"We aren't sure who the super-archaics were. They may have been Homo erectus, or Homo antecessor, or some other taxon that has not been named," lead author Alan Rogers, a professor in the Department of Anthropology at the University of Utah, told IFLScience.

"I suspect they were Eurasian, but a recent paper out of Sriram Sankararaman's lab finds evidence of super-archaic admixture in west Africa. In future research, it will be interesting to find out whether our super-archaics were the same as Sriram's," he said.

All of this might sound a bit hazy, but the evolutionary history of the Homo family is filled with many gaps in our knowledge and plenty of confusing interlinked plot points. We know that humans, Neanderthals, and Denisovans all widely interbred with each other on multiple historic occasions. However, other researchers have also found that our genetics contain the "ghosts" of many other large-brained hominins that we've never discovered the remains of. 

"It seems very clear that our family tree wasn't really a tree at all; it was more of a network. In the middle Pleistocene, there were apparently several hominin populations that had been separate for a long time but could still interbreed," Rogers added.

An evolutionary tree including four proposed episodes of gene flow. The previously unknown event 744,372 years ago (orange) suggests interbreeding occurred between super-archaics and Neanderthal-Denisovan ancestors in Eurasia. Adapted from Alan Rogers

Reporting in the journal Science Advances, the researchers reached these findings using computer modeling software that uses genetic data to understand the history of populations and the flow of DNA between them. The research gathered data from Neanderthals found in the Altai Mountains of Siberia and the Vindija Cave in Croatia, as well as from modern Europeans, then looked to understand how the various genetic combinations might have emerged using different models. 

This novel software method did not just reveal some insights into Neanderthal-Denisovan ancestors interbreeding with a distantly related hominin, it has also helped to shed light onto some of the murkier chapters of the human story. In 2017, this same project argued that Neanderthals split from Denisovans about 381,000 years ago. However, the new software found that the split was much earlier, suggesting that Neanderthals were already distinct from Denisovans 600,000 years ago

One of the big questions surrounding modern humans is the many waves of early human migrations out of Africa and into Eurasia. As per the new study, modern humans and their ancestors migrated from Africa into Eurasia in just three main waves: 1.9 million years ago, 700,000 years ago, and 50,000 years ago.

They also showed plenty more evidence that Neanderthals interbred with the ancestors of modern humans. However, that's no surprise if you take a look at own our DNA. It's long been clear that most people of European descent have some Neanderthal genes in their genome, but research released in January of this year showed that traces of Neanderthal DNA can be found in almost every modern population on Earth, even those living in Africa, where it's understood Neanderthals never stepped foot.

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