After decades of digging, paleoanthropologists looking for fossilized human bones have established a reasonably clear picture: Modern humans arose in Africa some 200,000 years ago and all archaic species of humans then disappeared, surviving only outside Africa, as did the Neanderthals in Europe. Geneticists studying DNA now say that, to the contrary, a previously unknown archaic species of human, a cousin of the Neanderthals, may have lingered in Africa until perhaps 25,000 years ago, coexisting with the modern humans and on occasion interbreeding with them.

The geneticists reached this conclusion, reported in the journal Cell, after decoding the entire genome of three isolated hunter-gatherer peoples in Africa, hoping to cast light on the origins of modern human evolution. But the finding is regarded skeptically by some paleoanthropologists because of the absence in the fossil record of anything that would support the geneticists’ statistical calculations.