Interbreeding among different ancient human species may have been more prevalent than originally thought offering fresh insights into how modern humankind evolved, The Wall Street Journal reported
The findings are leading scientists to rethink human evolution. For instance, there may have been many extinct human populations, that researchers have yet to discover, who interbred and exchanged DNA, The New York Times reported
In findings that provide insight into the chemistry of human heredity, researchers who analyzed the amazingly well-preserved DNA from a 400,000-year-old femur bone— part of the remains of 28 early humans who belonged to an unfamiliar species— found startling evidence of interbreeding, according to the Journal.
The extracted human DNA is the oldest ever discovered. The bones were found in a cave in northern Spain that scientists have been excavating since the 1970s.
The type of DNA analyzed is mitochondrial, which is transmitted unchanged from mother to child.
The bones belong to humans who were neither Neanderthals nor modern humans though the DNA sample overlapped with Denisovans — a branch of humanity discovered only in 2010 in Siberia.
Scientists can only speculate about who these people were: perhaps a separate species that had interbred with Denisovans; or related to ancestors of Denisovans; or ancestors of both Denisovans and Neanderthals; or related to an even more ancient human species, or all of the above.
Neanderthals, anatomically modern humans and Denisovans coexisted tens of thousands of years ago, scientists posit.
There is Neanderthal DNA in every modern non-African today and a bit of Denisovan in some people as well.
University of Arizona geneticist Michael Hammer said the discovery "tells us something interesting about how our species evolved. It may be that interbreeding was a common process in all of human evolution."
Juan-Luis Arsuaga, director of the Center for Contemporary Human Evolution at the Institute of Health Carlos III in Madrid, said scientists first thought the cave bones were Neanderthal relatives but "the mitochondrial genome told a different story. It was unexpected and shocking."
He said the cave was as a very special place.
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