A groundbreaking DNA study has confirmed what was suspected all along, that humans originated in Africa, on the South African-Namibian border.
The San people, hunter-gatherers in the area for thousands of years, are perhaps the oldest human population on Earth.
They are descended from the earliest human ancestors from which all other groups of Africans stem and, in turn, to the people who left the continent to populate other corners of the planet.
The origin of a species is taken to be the place where people show the most genetic diversity because of the time it takes for genes to evolve. Now DNA tests show that the Sans are genetically the most diverse. Hence perhaps the most ancient.
The research published in the online journal Science also showed that nearly three-quarters of African-Americans can trace their ancestry to West Africa.
The 10-year-study was led by Professor Sarah Tishkoff, a geneticist at the University of Pennsylvania.
She trekked across remote and dangerous areas of the continent with an international team collecting DNA samples from more than 3,000 modern Africans from 121 distinct populations.
Often working in primitive conditions, the researchers sometimes had to resort to using a car battery to power their equipment.
The tests revealed they had all descended from just 14 ancestral populations, and the languages they spoke were closely correlated with the variation of their genes.
The study also suggests that a small group of 150 Africans, who went on to populate the rest of the world, first left their continent from the Red Sea.
The researchers found people who lived in Sudan had genetic markers which suggested they were related to the group who moved abroad 50,000 years ago.
'The human genome describes the complexity of our species,' added Muntaser Ibrahim of the department of molecular biology at the University of Khartoum, Sudan.
'Now we have spectacular insight into the history of the African population ... the oldest history of mankind.
'Everybody's history is part of African history because everybody came out of Africa.'
Before this study very little was known about the genetic variation in Africans, knowledge that is vital to understanding why diseases have a greater impact in some groups than others and in designing ways to counter those illnesses.
Scott M. Williams of Vanderbilt University noted that constructing patterns of disease variations can help determine which genes predispose a group to a particular illness.
This study 'provides a critical piece in the puzzle', he said. For example, there are clear differences in prevalence of diseases such as hypertension and prostate cancer across populations, Mr Williams said.
Christopher Ehret from the University of California, Los Angeles, compared genetic variation among people to variations in language.
There are an estimated 2,000 distinct language groups in Africa broken into a few broad categories, often but not always following gene flow.
Movement of a language usually involves arrival of new people, Mr Ehret noted, bringing along their genes.
But sometimes language is brought by a small 'but advantaged' group which can impose their language without significant gene flow.
The study also found that about 71 per cent of African-Americans can trace their ancestry to western African origins.
They also have between 13 per cent and 15 per cent European ancestry and a smaller amount of other African origins.
There was 'very little' evidence for American Indian genes among African-Americans, Tishkoff said.
The study was funded by the National Cancer Institute, the National Institutes of Health, the Advanced Computing Center for Research and Education at Vanderbilt University, the L.S.B. Leakey and Wenner Gren Foundation, the National Science Foundation, the David and Lucile Packard and Burroughs Wellcome foundations.