Ann Gibbons
A middle ground may be emerging in a long-running dispute about human origins. One camp holds that our earliest ancestors arose in Africa and spread around the world more than 1 million years ago; modern humans then arose in many different regions. The other argues that modern humans arose in Africa and swept around the globe 100,000 years ago, completely replacing existing human populations on other continents. This Out-of-Africa view has been the favored contender, but new genetic data imply that some modern populations may have arisen in Asia and migrated back into Africa.