Scientists discover nested DNA of mysterious ancestor who mated with early humans

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Scientists discover nested DNA of mysterious ancestor who mated with early humans

Today's humans carry the genes of an ancient, unknown ancestor from a million years ago.

Scientists have discovered that we have a mysterious ancestor in our DNA. The ancestor was most likely Homo erectus, but we can't be sure because the extinct species has never been genetically sequenced. The new research, published in the journal PLOS Genetics , also finds that ancient humans mated with Neanderthals between 200,000 and 300,000 years ago, which was well before the earliest previously known mixing of the two species occurred, which occurred after Homo sapiens migrated in large numbers out of Africa and into Europe 50,000 years ago. Thanks to this ancient mixing event, Neanderthals actually owe between 3% and 7% of their genomes to ancient Homo sapiens, the researchers reported.

Some people have more than others, am I right?

"Our best conjecture is that an early group of anatomically modern humans left Africa then encountered and interbred with Neandertals, perhaps in the Middle East," said Adam Siepel, a computational biologist at Cold Spring Harbor Laboratory and one of the authors of a new paper. "This lineage [of humans] would then have been lost โ€” either gone extinct, or absorbed by the Neandertals, or migrated back to Africa."

Scientists have spent years studying how humans and Neanderthals mated while their populations overlapped in Europe, before Neanderthals went extinct around 30,000 years ago. As much as 1-4 percent of genes from people in Asia, Europe and Oceania came from Neanderthal ancestors, who went extinct 30,000 years ago. Thanks to these modern studies, scientists believe that as much as 20% of the Neanderthal genome may be preserved.

"We are trying to build a complete model for the evolutionary history of every segment of the genome, jointly across all of the analyzed individuals," Siepel said. "The ancestral recombination graph, as it is known, includes a tree that captures the relationships among all individuals at every position along the genome, and the recombination events that cause those trees to change from one position to the next."

"A picture is emerging of a series of distinct but related populations moving around the globe and frequently interacting with one another, with occasional interbreeding events that produced hybrid offspring," Siepel said. "These hybrid offspring might in some cases have suffered from reduced fitness โ€” this is an area of controversy โ€” but apparently many of them were healthy enough to survive and reproduce, leaving a patchwork of archaic and modern human DNA in Neanderthals and modern humans."

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