Southern Africa's bushmen, and their relatives the Khoe, veered off on their own path of genetic development 100,000 years ago, according to a new study this week.
The split, gleaned from an analysis of genetic data, is the earliest divergence scientists have discovered in the evolution of modern humans.
The Khoe and the San peoples -- who speak click languages, and live across a wide swath of southern Africa from Namibia to Mozambique to South Africa -- have long fascinated scientists.
The San, in particular, were one of the last remaining hunter-gatherer societies, living well into the 20th century in a style anthropologists think was similar to humans' most ancient ancestors.
The study published in the journal Science on Thursday analyzes the genes of 220 members of the Khoe and San groups. Researchers looked at 2.3 million genetic variations for each participant, an unprecedented number, learning important information about the Khoe-San and, more generally, the origins of modern humans.
The analysis made it clear that there is not a "coherent picture" of where the cradle of modern man was located.
Archeological data would point to East Africa, while other studies suggest it was in southern Africa.
But according to their analysis, "different parts of Africa show up as potentially being the origin of anatomically modern humans," said Mattias Jakobsson, of Sweden's Uppsala University.
Based on the genetic variations they saw in their subjects, "different groups of humans contributed genes to this pool that then later on became anatomically modern humans," he said in a telephone press conference.
The study also gave new evidence for how and when the practice of raising livestock, known as pastoralism, started spreading to southern Africa.
The Nama, a Khoe group in Namibia who lived as herders, was genetically very similar to their cousins among the southern San, who traditionally lived as hunter-gatherers.
However, "a small but very distinct" component of Nama genes are similar to a group of East Africans, also traditionally herders, who likely were the incomers that introduced the Khoe to pastoralism, explained co-author Carina Schlebusch in a statement.
The study also showed evidence of local adaptation among the different Khoe and San groups.
Researchers discovered indications that natural selection among the ancient populations led to gene variations involved in muscular function, immune response and skin protection against ultraviolet rays.
"Although all humans today carry similar variants in these genes, the early divergence between Khoe-San and other human groups allowed us to zoom-in on genes that have been fast-evolving in the ancestors of all of us living on the planet today," said Pontus Skoglund, another co-author.
[image via Agence France-Presse]