Africa cradle of humankind, study shows

Modern humans took their first steps to colonise the world from a single region of sub-Saharan Africa, according to British scientists.

Many scientists have long thought humankind emerged from the continent some 56,000 years ago, before spreading northwards and establishing Stone Age cultures across Asia, Europe and Australia. But some have argued that separate populations of Homo sapiens arose in different regions, before independently taking over fresh territories as their populations grew.

Andrea Manica and Bill Amos at Cambridge University used a combination of genetics and skull measurements to show modern humans could not have emerged in different places, but instead came from one region of southern central Africa.

The researchers examined genetic diversity in 53 human populations across the world and found that the further those populations were from Africa the less varied their genetic make-up. The smooth fall in genetic diversity away from Africa suggests smaller groups of humans spread out from a single area.

"It's thought that Africa's population was large but for some reason people started moving out of Africa and spreading out to colonise the world. As they did so, their population sizes went down, and because of that, they started losing genetic variability," said Dr Amos.

The researchers then looked at variations in the size and shape of 6,000 skulls around the world. Again, they found that those from populations most distant from Africa showed the least variety. "As genetic variability was lost when humans spread out, the variability in their appearance also declined," Dr Amos said.

The study appears in Nature.