Out of Africa: more evidence for single origin hypothesis

Modern humans probably did evolve in Africa, a Nature study published this week suggests.

Dr Andrea Manica and colleagues took multiple measurements from over 4,500 male skulls drawn from 105 populations around the world and combined the results with known genetic information.

Genetic analyses have supported the idea of a single location, all pointing to Africa as the putative cradle of modern humans.

Studies of cranial data, however, have provided mixed results, the researchers say, leading some to argue that there could have been multiple origins of modern humans.

The new study has found that phenotypic diversity decreased with distance from Africa, mirroring the loss of genetic diversity.

"Indeed, distance from Africa accounted for an average of up to a quarter of heritable variation in skull measurements - a remarkable proportion for traits known to be under selection," the researchers say.

Such a pattern indicates that all populations come from the same shared group of ancestors who gradually migrated further away from Africa over thousands of years.

Their genetic and physical diversity would have been narrowed down by "bottlenecks", or events that temporarily reduced the population during migration, such as natural disasters.

"The origin of anatomically modern humans has been the focus of much-heated debate," Manica, from Cambridge's Department of Zoology, said.

"Some have used skull data to argue that modern humans originated in multiple spots around the world. We have combined our genetic data with new measurements of a large sample of skulls to show definitively that modern humans originated from a single area in sub-Saharan Africa."

To ensure the validity of their single origin evidence, the researchers attempted to use their data to find non-African origins for modern humans.

Researcher Dr Francois Balloux said that to test the alternative theory for the origin of modern humans, the team tried to find an additional, non-African origin, but it did not work, suggesting a single point of origin.

"The effect of ancient population bottlenecks on human phenotypic variation" is published in the July 19 issue of Nature.