Michael Balter in ScienceNOW Daily News:
The fight over modern human origins is heating up. A new study of thousands of human skulls claims to confirm genetic evidence that our species arose in Africa and then spread over the globe. But some researchers say that an alternative scenario has not been ruled out.
Researchers have long debated two opposing hypotheses for modern human origins. According to the Out of Africa hypothesis, our ancestors appeared in Africa about 200,000 years ago and then replaced all other human species, including Homo erectus and the Neandertals, with little or no interbreeding. The multiregional hypothesis holds that modern humans emerged from populations of “archaic” hominids in Africa, Europe, and Asia that evolved locally but also exchanged genes. Numerous genetic studies support the single-origin model, finding that the genetic diversity of today’s human populations is greatest in Africa and decreases steadily with distance from that continent. The idea is that diversity declined because each group of migrants founded a new population, creating genetic bottlenecks. But some researchers see traces of mixing between moderns and archaics in the genetic data.