Washington: A new study by geneticists at Stanford University and the Russian Academy of Sciences have found that human beings may have made their first journey out of Africa as recently as 70,000 years ago.

The researchers estimate that the entire population of ancestral humans at the time of the African expansion consisted of only about 2,000 individuals.

"This estimate does not preclude the presence of other populations of Homo Sapiens (modern humans) in Africa. Although, it suggests that they were probably isolated from one another genetically and that contemporary worldwide populations descend from one or very few of those populations," said Marcus W Feldman, the Burnet C and Mildred Finley Wohlford professor at Stanford and co-author of the study.

The small size of our ancestral population may explain why there is so little genetic variability in human DNA compared with that of chimpanzees and other closely related species.

"Our results are consistent with the "out-of-Africa" theory, according to which a sub-Saharan African ancestral population gave rise to all populations of anatomically modern humans through a chain of migrations to the Middle East, Europe, Asia, Oceania and America," Feldman noted.

Since all human beings have virtually identical DNA, geneticists have to look for slight chemical variations that distinguish one population from another. One technique involves the use of "microsatellites" – short repetitive fragments of DNA whose patterns of variation differ among populations.

Because microsatellites are passed from generation to generation and have a high mutation rate, they are a useful tool for estimating when two populations diverged.

In their study, the research team compared 377 microsatellite markers in DNA collected from 1,056 individuals representing 52 geographic sites in Africa, Eurasia (the Middle East, Europe, Central and South Asia), East Asia, Oceania and the Americas.

Statistical analysis of the microsatellite data revealed a close genetic relationship between two hunter- gatherer populations in sub-Saharan Africa – the Mbuti pygmies of the Congo Basin and the Khoisan (or "bushmen") of Botswana and Namibia. These two populations "may represent the oldest branch of modern humans studied here", the authors concluded.

ANI