Homo Sapiens Descended from a Single Small Population

The first exodus of humans from Africa took place about 66,000 years ago
According to DNA analyses, the descendants of modern man migrated for the first time from Africa some 70,000 years ago and then settled all over the world. Geneticists from  Stanford University and the Russian Academy of Sciences have recently conducted research and came to this conclusion. An article about their work was published in the magazine Human Genetics. In the article, the scientists explained how they had arrived at the conclusion that the population of the first-ever group to migrate from Africa amounted to about 2,000 people. "This estimate does not preclude the presence of other populations of homo sapiens in Africa, although it suggests that they were probably isolated from one another genetically, and that the contemporary worldwide populations are descended from one group or from a very small number of groups," Marcus W. Feldman of Stanford University, and a co-author of the study, said.

If all humans originate from one and the same ancestral population in Africa,  it is easy to explain the small amount of divergence in human genetic diversity. "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 nearly identical DNA, geneticists need to look for slight chemical variations that distinguish one population from another. In the study, scientists compared 377 markers in DNA collected from 1,056 individuals representing 52 different geographical areas in Africa, Eurasia (the Middle East, Europe, Central and South Asia), East Asia, Oceania and the Americas. Statistical analysis of the data revealed close genetic ties between two hunter-gatherer settlements in Africa that lived in the area of the Sahara, the Congo Basin, Botswana and Namibia. The two settlements "may represent the oldest branch of modern humans studied here," the authors concluded. The data showed a genetic split between the ancestors of those hunters-gatherers (pygmies) and the ancestors of contemporary agricultural African people in many countries in southern Africa. "This division occurred between 70,000 and 140,000 years ago and was followed by an expansion out of Africa into Eurasia, Oceania, East Asia and the Americas - in that order," Professor Feldman said.

This result corresponds to a previous study in which Feldman and other scientists analyzed the Y chromosomes of more than 1,000 males from 21 modern countries. As a result of the study, the researchers concluded that the first human migration from Africa took place about 66,000 years ago. In contrast to hunters and gatherers, the ancestors of the people who live in the African farming settlements in the area of the Sahara started developing new lands and increasing the size of their populations, which began approximately 35,000 years ago. "This increase in population sizes might have been preceded by technological innovations that led to an increase in survival rates and then an increase in the overall birth rate," the authors wrote. Eurasian and East Asian peoples also showed a population expansion, which started about 25,000 years ago.

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