Human DNA shows early humans got intimate with unidentified, ancient ancestor

Human DNA shows early humans got intimate with unidentified, ancient ancestor
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A study of ancient DNA has found that when it came to picking intimate partners, our early ancestors weren't all that picky. 

Scientists at New York's Cornell University have discovered that DNA from an ancient, unidentified ancestor has been passed down to modern humans. The new analysis of ancient genomes indicates that different branches of the human family tree interbred multiple times, meaning some humans alive today carry DNA from the archaic ancestor.

A new algorithm developed by the scientists suggests ancient humans and related species interbred early - and often. 

According to the study, a group of early humans migrated out of Africa and interbred with Neanderthals in Eurasia roughly 50,000 years ago. But the sequencing of genomes from Neanderthals and the Denisovans - a less well-known species of archaic human that ranged across Asia - has given researchers new insight into the movements and interbreeding of ancient groups.  

The aforementioned algorithm allows researchers to identify segments of DNA originating from other species - even if it came from an unidentified source and the interbreeding occurred thousands of years ago. 

The algorithm was used to analyse genomes from two Neanderthals, a Denisovan and two African humans. Researchers found evidence that 3 percent of the Neanderthal genome came from ancient humans, the interbreeding estimated to have occurred between 200,000 and 300,000 years ago. One percent of the Denisovan genome likely came from an unknown and more distant relative - speculated to be Homo erectus. About 15 percent of this "super-archaic" DNA may have been passed down to modern humans alive today.

Researchers believe interbreeding is likely to have occurred whenever two groups overlapped in time and space. 

"What I think is exciting about this work is that it demonstrates what you can learn about deep human history by jointly reconstructing the full evolutionary history of a collection of sequences from both modern humans and archaic hominins," author Adam Siepel said in a statement accompanying the release of the study. 

"This new algorithm is able to reach back further in time than any other computational method I've seen. It seems to be especially powerful for detecting ancient introgression."

According to Scimex, the algorithm may be useful for studying gene flow in other species where interbreeding occurred, such as in wolves and dogs.  

The study's findings were released on Thursday (local time) in PLOS Genetics.