One of the best-known theories about human evolution—that the ancestors of Homo sapiens originated in Africa before populating the rest of the world 2 million years ago—is coming under fire. In a challenge to conventional wisdom, Robin Dennell of the University of Sheffield in England and Wil Roebroeks of Leiden University in the Netherlands argue that the "out of Africa" interpretation is built on shaky evidence. Maybe, they say, it is time to look to Asia instead.
Roebroeks and Dennell point out that recent fossil finds in the nation of Georgia suggest an Asian origin as much as an African one. "We know so little about Asia—and, for that matter, Africa—that we should be very careful not to turn a hypothesis into a stone-carved truth simply by repeating it too often," Roebroeks says. "We need comparable data sets from both continents."
Anthropologist Spencer Wells, whose genetic research supports a single African origin, welcomes this questioning of the status quo. "That Homo erectus could have origins in Asia would be potentially shocking," he says, "but I think that what Roebroeks and Dennell are saying reflects the state of the field. We certainly don't have enough fossils. Perhaps we are never going to be able to test this hypothesis."
Meanwhile, population geneticist Alan Templeton of Washington University in St. Louis is overturning ideas about human origins from another angle. He has analyzed genetic relationships among diverse groups of people and finds that today's humans show evidence of interbreeding among Homo erectus, Homo sapiens, and other early hominids over a wide span of time, from as far back as 1.5 million years ago until the last hypothesized global migration, around 80,000 years ago. Templeton concludes that the humans who departed from Africa probably interbred with other early humans in Europe and Asia, contradicting the widely held notion that the Africans wiped out existing populations as they moved.
"We don't have a tree of human populations with branches for Europeans and Asians and Arabs," Templeton says. "It's more like a trellis: Things are intertwined."