Artist's impression of a Neanderthal hunter. New evidence suggests the Neanderthals and modern humans interbred.
Credit: American Museum of Natural History
SYDNEY: Modern humans contain a little bit of Neanderthal, according to a new theory, because the two interbred and became one species.
The theory is the latest addition to the ongoing debate about what happened to this early species of human.
In a paper published this week in the U.S. journal Proceedings of the National Academy of Sciences, a team of European researchers report a "mosaic of modern human and archaic Neanderthal features" in 30,000 -year-old human fossils from Romania.
Co-author Erik Trinkaus from Washington University explains: "[Some] closely related species of mammals freely interbreed, produce fertile viable offspring, and blend populations." This is what appears to have happened with Neanderthals and modern humans, he says.
Shorter and stouter than modern humans, but with larger brains, Neanderthals lived in Europe, central Asia and the Middle East for about 170,000 years before disappearing between 33,000 to 24,000 years ago.
Their extinction coincided with the migration of modern humans out of Africa and across Europe. Few mysteries in the history of human ancestry have been as hotly debated as what caused the extinction of the Neanderthals.
Some scientific theories have Neanderthals dying out because they were less well-adapted to the climate changes that occurred across Europe at that time. Others cite evidence of a more brutal end, in which Neanderthals were slaughtered by modern humans.
This new study helps to settle the controversy. According to the researchers, the populations probably blended together through sexual reproduction. "Extinction through absorption is a common phenomenon," says Trinkaus.
The human remains were found in Pestera Muierii ('Cave of the Old Woman'), an elaborate cave system in Romania. First uncovered in 1952, the fossils remained poorly dated and largely ignored until recently.
Using carbon dating techniques, Trinkaus and colleagues found that the remains were 30,000 years old. Their analysis of the bones revealed diagnostic skeletal features of modern humans, including smaller eyebrow ridges, very narrow holes where the nostrils join the skull, and a shin bone that is flat on one side and concave on the other.
However the mostly human skeletons also possessed distinct Neanderthal features; features that were not present in ancestral modern humans in Africa. These include a large bulge at the back of the skull, a more prominent projection around the elbow joint, and a narrow socket at the shoulder joint.
Further analysis of one skeleton's shoulder showed that these humans did not have the full set of anatomical adaptations for throwing projectiles, such as spears, during hunting.
According to the researchers, this mixture of human and Neanderthal features suggests that a complicated reproductive scenario existed as humans and Neandertals interbred. The hypothesis that the Neanderthals were simply replaced should therefore be abandoned, they suggest.
Trinkaus says we may carry some of the genetic legacy of the Neanderthals within us. However it would be difficult to determine which of us are more closely related to the Neanderthals: "there has been 30,000 to 35,000 years of human evolution since then," he says.
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