There has been a number of studies coming out recently on Khoesan genetics but this one does not seem to be just redundant, providing some extra information instead.
Desiree C. Petersen et al., Complex Patterns of Genomic Admixture within Southern Africa. PLoS Genetics 2013. Open access → LINK [doi:10.1371/journal.pgen.1003309]
Within-population genetic diversity is greatest within Africa, while between-population genetic diversity is directly proportional to geographic distance. The most divergent contemporary human populations include the click-speaking forager peoples of southern Africa, broadly defined as Khoesan. Both intra- (Bantu expansion) and inter-continental migration (European-driven colonization) have resulted in complex patterns of admixture between ancient geographically isolated Khoesan and more recently diverged populations. Using gender-specific analysis and almost 1 million autosomal markers, we determine the significance of estimated ancestral contributions that have shaped five contemporary southern African populations in a cohort of 103 individuals. Limited by lack of available data for homogenous Khoesan representation, we identify the Ju/’hoan (n = 19) as a distinct early diverging human lineage with little to no significant non-Khoesan contribution. In contrast to the Ju/’hoan, we identify ancient signatures of Khoesan and Bantu unions resulting in significant Khoesan- and Bantu-derived contributions to the Southern Bantu amaXhosa (n = 15) and Khoesan !Xun (n = 14), respectively. Our data further suggests that contemporary !Xun represent distinct Khoesan prehistories. Khoesan assimilation with European settlement at the most southern tip of Africa resulted in significant ancestral Khoesan contributions to the Coloured (n = 25) and Baster (n = 30) populations. The latter populations were further impacted by 170 years of East Indian slave trade and intra-continental migrations resulting in a complex pattern of genetic variation (admixture). The populations of southern Africa provide a unique opportunity to investigate the genomic variability from some of the oldest human lineages to the implications of complex admixture patterns including ancient and recently diverged human lineages.
The array of Khoesan populations senso stricto
analyzed in this study is much smaller than that of Schebusch 2010
but this study has the advantage of including Cape Coloureds and their Baster relatives, partially descendants from the otherwise extinct pastoralist Khoekhoe (Hottentots
, now considered a derogative term) who lived in much of Southern Africa upon the arrival of Bantu and Europeans, as well as the amaXhosa, a Bantu people which clearly display marked Khoesan admixture.
|Figure 1. Map of southern Africa
showing distribution of sampling per population identifier and
significant historical events that likely shaped ancestral
There is brief mention of maternal and paternal DNA. Just to mention that mtDNA being mostly aboriginal (L0d/L0k) among the Khoesan (86-100%), the Coloureds (68%) and even the Xhosa (47%, all L0d), while aboriginal Y-DNA (essentially A2b and A2c2, plus occasional B2) is concentrated among the Ju/’hoan, with the !Xun being instead dominated by E1b1-M275, of putative East African (Nilotic?) origins. This is consistent with the !Xun being historically pastoralists. European patrilineages, notably R1b, are dominant among the Baster (92%) and Cape Coloured (71%).
only make up some 9% of South African population but they dominate the countryside in much of the former Cape Province. Namibian Basters
are a subset of them who migrated northwards in 1868.
|Figure 2. PCA and STRUCTURE analysis (click to expand)
We can see in the graphics above how the North Cape Coloured and Baster only display minor Bantu admixture, being essentially a variable mix of European and Khoesan ancestry, with probably also some Malay input (apparent in the increase of the blue component relative to the European reference). Instead East Cape and Cape Town (D6) Coloured appear to have greater apportion of Bantu ancestry and, especially the later, a notable increase of the East Asian input.
The STRUCTURE graph, particularly at K=9, is also informative about other African populations but I won’t dwell in that here.
The authors also made an interesting exercise of analysis using Ancestry Informative Markers with the !Xun and Xhosa:
|Figure 4. Ju/’hoan-Yoruba ancestry
informative markers (AIMs) defined ancestral contributions to the !Xun
and amaXhosa, providing evidence for two distinct !Xun lineages with
differing ancestral contributions.
It seems evident that much of the !Xun ancestry (up to 70%) does not fall in either (Ju/’hoan-Yoruba) category but it is something else, probably specific to this people. The Xhosa Khoesan ancestry also seems closer to the pastoralist !Xun than to the (likely more genuinely ancient) Ju/’hoan.
There is some more info in the paper but I feel that the essentials are sufficiently covered here.