Newly discovered bits of "foreign DNA" in modern Africans indicate that a mysterious "sister species" may have walked the earth with Neanderthals and humans, according to scientists. The DNA doesn't resemble DNA from any modern-day humans, nor from Neanderthals, whose DNA sometimes shows up in modern-day Europeans. "We're calling this a Neanderthal sibling species in Africa," said Joshua Akey of the University of Washington. He believes human interbreeding occurred with the mystery species 20,000 to 50,000 years ago when Neanderthals were waning in Europe, and modern humans were beginning to spread out from Africa, reports the Washington Post.
A skull with unusual features found in Nigeria could be a remnant from the vanished species, notes the Post. Many scientists are not surprised that another species—and even others—existed and died out in the shadow of us. But others are skeptical, particularly because of the dearth of fossil and archaeological evidence. Stanford paleoanthropologist Richard Klein told the New York Times that it's irresponsible for geneticists to publish findings on the origin of humans without trying to reconcile them with fossil and archeological evidence. (Read more cavemen stories.)