Science and environment reporter, BBC News

Modern humans may have originated from southern Africa, an extensive genetic study has suggested.

Data showed that hunter-gatherer populations in the region had the greatest degree of genetic diversity, which is an indicator of longevity.

It says that the region was probably the best location for the origin of modern humans, challenging the view that we came from eastern Africa.

The study appears in the Proceedings of the National Academy of Sciences.

"Africa is inferred to be the continent of origin for all modern human populations," the international team of researchers wrote.

"But the details of human prehistory and evolution in Africa remain largely obscure owing to the complex histories of hundreds of distinct populations."

'Very exciting'

Co-author Brenna Henn, from Stanford University, California, said the team's study - the most comprehensive of its kind - reached two main conclusions.

"One is that there is an enormous amount of diversity in African hunter-gatherer populations, even more diversity than there is in agriculturalist populations," she told BBC News.

"These hunter/gatherer groups are highly structured and are fairly isolated from one another and probably retain a great deal of different genetic variations - we found this very exciting."

Dr Henn added: "The other main conclusion was that we looked at patterns of genetic diversity among 27 (present-day) African populations, and we saw a decline of diversity that really starts in southern Africa and progresses as you move to northern Africa."

She explained that the team's modelling was consistent with the serial founder effect. This refers to a loss of genetic variation when a new population is established by a very small number of individuals from the original, larger population.

"Populations in southern Africa have the highest genetic diversity of any population, as far as we can tell.

"So this suggests that this might be the best location for (the origins) of modern humans."

'Landmark study'

Chris Stringer, a leading palaeontologist based at the Natural History Museum, London, said: "The new paper... suggests that the genes of the Namibian and Khomani bushmen (southern Africa), Biaka pygmies (Central Africa) and the Sandawe (East Africa) appear to be the most diverse, and by implication these are the most ancient populations of Homo sapiens."

Professor Stringer, who was not involved in the study, added: "This is a landmark study, with far more extensive data on... hunter gatherer groups than we have ever had before, but I am cautious about localising origins from it."

He said that the ranges of these groups were currently quite limited, but rock paintings by ancient populations that had been linked to the Bushman hinted that they were once far more widespread.

"It seems more likely that the surviving hunter-gatherer groups are now localised remnants of populations that formerly ranged across much of sub-Saharan Africa 60,000 years ago," he told BBC News.

Professor Stringer said that he no longer thought that there was a single "Garden of Eden" where we evolved. Instead, he said, "distinct populations in ancient Africa probably contributed to the genes and behaviours that make up modern humans".