The San people of southern Africa, who have lived as hunter-gatherers for thousands of years, are likely to be the oldest population of humans on Earth, according to the biggest and most detailed analysis of African DNA. The San, also known as bushmen, are directly descended from the original population of early human ancestors who gave rise to all other groups of Africans and, eventually, to the people who left the continent to populate other parts of the world.

A study of 121 distinct populations of modern-day Africans has found that they are all descended from 14 ancestral populations and that the differences and similarities of their genes closely follows the differences and similarities of their spoken languages.

The scientists analysed the genetic variation within the DNA of more than 3,000 Africans and found that the San were among the most genetically diverse group, indicating that they are probably the oldest continuous population of humans on the continent – and on Earth.

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The study, published in the journal Science, took 10 years of research involving trips to some of the most remote and dangerous parts of Africa to collect blood samples. The project found modern Africans had the most diverse DNA of all racial groups in the world, confirming the idea that Africa is the birthplace of humanity, said Sarah Tishkoff of the University of Pennsylvania.

The scientists also found genetic "markers" in the DNA of the present-day inhabitants of East Africa living near to the Red Sea, which indicated that they belonged to the same ancestral group who migrated out of Africa to populate Asia and the rest of the world. West Africans speaking the Niger-Kordofanian language were found to share many genetic traits with African-Americans, indicating they were the ancestors of most of the slaves sent to the New World.

One of the main findings to emerge was the genetic similarity between groups who shared similar languages despite living many thousands of miles from one another. The Sandawe and Hadza of Tanzania shared common ancestors with the Khoisan speakers of southern Africa: all three groups speak "click" languages.