Most researchers agree that modern humans got their start in Africa and then spread throughout the world beginning about 50,000 years ago. But scientists are still working out the details of how the planet was peopled, such as who went where, and when. A new study, employing sophisticated modeling techniques, confirms the prevailing Out of Africa model but also comes up with some surprises, including evidence that the Americas' first human inhabitants arrived in multiple waves.

Archaeologists and anthropologists worldwide have dug up plenty of skeletons over the years, but the bones seldom say much about where ancient peoples originally came from. Thus researchers have tried using variations in the genes of living individuals to trace their ancestries back to prehistoric times. In general, the closer two modern populations are genetically, the more likely that they share a common ancestry; yet this ancestral heritage is sometimes obscured by genetic changes that have taken place over thousands of years, as well as by interbreeding between populations. Happily, efforts to get around these complications have been boosted by an ever-growing mound of data about genetic differences between human populations.

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Courtesy Science Mag