Scientists have long held that modern humans originated in Africa because that's where they've found the oldest bones. Geneticists have come to the same conclusion by looking at Africa's vast genetic diversity, which could only have arisen as DNA changed over many thousands of years.

There's less agreement about the routes our ancestors took in their journey out of Africa and around the planet. Early migrations stalled but left behind evidence such as a human skull from 92 000 years ago at Qafzeh, Israel. Those people may have taken a northern route through the Nile Valley into the Middle East. But other emigrants who left Africa tens of thousands of years later could also have taken a different route: across the southern end of the Red Sea.

Scientists say these more recent wanderers gave rise to the 5.5 billion humans living outside Africa today. "I think the broad human prehistoric framework is in place," says geneticist Peter Forster of the McDonald Institute for Archaeological Research in Cambridge, England, "and we are now fitting in the details.

Look at the map below to identify the Red Sea and Qafzeh, Israel. Why does this map propose two different routes out of Africa? Wouldn't one be simpler?

Map from archeology.org - archive

Text in this section from National Geographic - Human Journey, Human Origins http://ngm.nationalgeographic.com/ngm/0603/feature2/map.html