Genetic Studies
In the 1990s, genomic studies of different peoples around the world found that the Y chromosome of Khoisan men (using samples drawn from several San tribes) share certain patterns of polymorphisms that are distinct from the genomes of all other populations. As the Y chromosome is highly conserved from generation to generation, this type of DNA testing is used by geneticists to determine when different subgroups separated from one another and hence their last common ancestry. The authors of these studies suggested that the Khoisan (actually the San) may have been one of the first populations to differentiate from the most recent common paternal ancestor of all extant humans, the so-called Y-chromosomal Adam by patrilineal descent, estimated to have lived 60,000 to 90,000 years ago. The authors also note that their results should be interpreted as only finding that the Khoisan "preserve ancient lineages", and not that they "stopped evolving" or are an "ancient group", since subsequent changes in their population are in parallel and similar to those of all other human populations.
Various Y-chromosome studies since confirmed that the Khoisan carry some of the most divergent (oldest) Y-chromosome haplogroups. These haplogroups are specific sub-groups of haplogroups A and B, the two earliest branches on the human Y-chromosome tree.
Similar to findings from Y-Chromosome studies, mitochondrial DNA studies also showed evidence that the Khoe–San people carry high frequencies of the earliest haplogroup branches in the human mitochondrial DNA tree. The most divergent (oldest) mitochondrial haplogroup, L0d, have been identified at its highest frequencies in the southern African Khoe and San groups. The distinctiveness of the Khoisan in both matrilineal and patrilineal groupings is a further indicator that they represent a population historically distinct from other Africans.
Read more about this topic: Khoisan
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