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Cape Coloureds

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A Cape Coloured family


I’ve mentioned the Cape Coloureds of South Africa on this weblog before. Culturally they’re Afrikaans in language and Dutch Reformed in religion (the possibly related Cape Malay group is Muslim, though also Afrikaans speaking traditionally). But racially they’re a very diverse lot. In this way they can be analogized to black Americans, who are about ~75% West African and ~25% Northern European, with the variance in ancestral proportions being such that ~10% are ~50% or more European in ancestry. The Cape Coloureds though are much more complex. Some of their ancestry is almost certainly Bantu African. This element is related to the West African affinities of black Americans. And, they have a Northern European element, which likely came in via the Dutch, German, and Huguenot settlers (mostly males). But the Cape Coloureds also have other contributions to their genetic heritage. Firstly, they have Khoisan ancestry, whether from Bushmen or Khoi. This is well known in their oral memory. The the hinterlands of the Cape of Good Hope are beyond the ecological range of the Bantu agricultural toolkit, so the region was still dominated by the Khoisan when the Europeans arrived. But there are also other suggestions of ancestry from Asia. The existence of the Cape Malays, whose adherence to Islam derives from the Muslims slaves brought by the Dutch, hints at likely relationships to the populations of maritime Southeast Asia. Finally, there are the Indians. This element is not too well recalled in cultural memory. But the Dutch brought many slaves from India as well as Southeast Asia. The Dutch first governor of the Cape Colony had a maternal grandmother who was an Indian slave, by various accounts Goan or Bengali (the town of Stellensbosch is named for him). No doubt it was far more likely that the usual lot of the descendants of Indian slaves during the Dutch era would be to be absorbed into the melange of the Coloured population than assimilated into what later became the Afrikaners.

Why is this aspect of Cape Coloured ancestry forgotten? I think part of the reason is that there is a large South African Indian community present today, but that community post-dates the Dutch period, and arrived with the British. When South Africans think of Indians they think of these people. Interestingly when the new genetic studies confirming Indian ancestry came on the scene I was “corrected” several times by Indians themselves when reporting this part of the Coloured heritage. They were under the impression I must be mistaken, as no one was familiar with the Cape Coloureds having Indian ancestry. Unfortunately pointing to PCA and STRUCTURE plots did not clear up the confusion.

In any case, thanks to the African Ancestry Project I now have three unrelated Coloured samples (I have more, but they are related). Since AAP is Afrocentric I thought it would be appropriate to run the Coloured samples separate first. So that’s what I did.

First, the methodology. I took the Gujaratis, Utah whites, Chinese from Denver, and Luhya (Bantu) from Kenya, and merged them with the Bushmen from the Henn et al. thick-marker data set. I also decided to add in the Yemeni Jews from Behar et al., mostly to check that the West Eurasian ancestry of the Cape Coloureds was in fact Northern European. I limited the Gujarati sample to those from “Gujarati_B”, which is the “more South Asian” cluster within the HapMap data set. I also reduced the numbers for a lot of HapMap populations. I’m looking at inter-continental differences, so I assumed that N of ~20 would suffice. After merging these data sets with the Cape Coloured samples I pruned all the missing SNPs. This left me with ~230,000 markers. In my experience this is kind of overkill for ADMIXTURE at this level of genetic distance between the hypothetical parent populations, but better safe than sorry. I also ran the samples through EIGENSOFT to generate PCAs. Also know that I performed a few “trials” with Sandawe and Hadza from Henn et. al., as well as with larger samples from the HapMap. That either added nothing on the margin, or just got confusing (there’s not really too much Sandawe and Hadza in the Cape Coloureds beyond what the Bantu must have picked up).

After I ran ADMIXTURE up to K = 7 it was clear that the optimal point in terms of informativeness was K = 6. You can see that the Cape Coloured samples have Northern European, Khoisan, Bantu African, Indian, and East Asian ancestry. There is a Yemeni component in two of the Coloured individuals which begs to be explained. This component is too high to be explained by Northern European ancestry alone. It could be explained by slaves from the Muslim Arab world. Also, the Indian reference sample used here was pruned to be very homogeneous. The slaves from South Asia were almost certainly much more diverse than the Gujarati_B population, which is mostly a group of Patels. Finally, sometimes when you run ADMIXTURE you see that combinations of atypical genetic backgrounds (e.g., Khoisan + Chinese) can general components which are likely artifacts. This tends to be an issue when you have two components which aren’t normally found together, and one is at a far lower level than the other. I’ve noticed this in particular with people with low amounts of Sub-Saharan African ancestry and Eurasian genetic backgrounds. They often come out to be East African or Pygmy or Bushmen when the probability of this is likely to be very low a priori. Notice that a few of the Bushmen have the Yemeni component but nothing else besides what you’d expect. This to me increases the likely that the light green in the Coloureds is also an artifact of the Khoisan genetic background against one of the other components.

So below is the K = 6 ADMIXTURE plot, along with the informative PCA’s. Observe that the three Coloureds have IDs.

Image Credit: Wikimedia Commons.

(Republished from Discover/GNXP by permission of author or representative)
 
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cape1Several months ago I put up a post which reviewed the geographical connections within the total genome content of the Cape Coloureds of South Africa. These peoples (plural because distinctive ethnic groups such as the Griqua were subsumed into this category in the 20th century) are of diverse origin, though generally their African and European ancestry has been highlighted. To the left I’ve reedited a plot which illustrates the inferred proportion of ancestry from various groups in modern Cape Coloured populations. Note that there is a substantial proportion of Asian ancestry, both South and East Asian. This makes historical sense as during the period of the founding of the Cape Colony a substantial number of Southeast and South Asian slaves were transferred from the Dutch East Indies, as well as from Madagascar, which itself has a Southeast Asian component in its population. Additionally, observe that the Bushmen & Khoikhoi element has been separated from the Bantu element. Archaeologists assume that the former are indigenous to South Africa, while the latter arrived within the last 2,000 years as the edge of the Bantu expansion which swept out of Nigeria east and south. These two populations are obviously both African, but their common ancestry is very deep. In some phylogenies Bushmen may be represented as the outgroup to all other human lineages, implying that one has to go very far back indeed for a common ancestor. In other words, the Bushmen are not the “oldest” human population, but have the oldest point of common ancestry with other human populations (e.g., the last common ancestor between a European and an East Asian may be ~30,000 years ago, but that between a Bushmen and a European may be ~80,000 years ago).

But these studies do not tell us everything about the demographic history behind the ethnogenesis of the Cape Coloureds. In this case uniparental lineages, mtDNA which traces the matriline and and nonrecombinant Y chromosomes (NRY) which trace the patriline may offer some value. Unfortunately too often because of methodological considerations we have looked at the uniparental lineages first, and then the total genome content, which I think inverts the optimal order in terms of putting genetic findings in context. A new study focuses on the Cape Coloured mtDNA and NRY lineages, with the previous findings in mind, Strong maternal Khoisan contribution to the South African coloured population: a case of gender-biased admixture:

The study of recently admixed populations provides unique tools for understanding recent population dynamics, socio-cultural factors associated with the founding of emerging populations, and the genetic basis of disease by means of admixture mapping. Historical records and recent autosomal data indicate that the South African Coloured population forms a unique highly admixed population, resulting from the encounter of different peoples from Africa, Europe, and Asia. However, little is known about the mode by which this admixed population was recently founded. Here we show, through detailed phylogeographic analyses of mitochondrial DNA and Y-chromosome variation in a large sample of South African Coloured individuals, that this population derives from at least five different parental populations (Khoisan, Bantus, Europeans, Indians, and Southeast Asians), who have differently contributed to the foundation of the South African Coloured. In addition, our analyses reveal extraordinarily unbalanced gender-specific contributions of the various population genetic components, the most striking being the massive maternal contribution of Khoisan peoples (more than 60%) and the almost negligible maternal contribution of Europeans with respect to their paternal counterparts. The overall picture of gender-biased admixture depicted in this study indicates that the modern South African Coloured population results mainly from the early encounter of European and African males with autochthonous Khoisan females of the Cape of Good Hope around 350 years ago.

The main results are in figure 2 & 3. The top left panel shows the mtDNA variation on an MDS chart in relation to other populations, “SAC” = South African Coloureds. The bottom left panel shows NRY variation. And the right panel shows the estimated admixture for mtDNA and NRY by population.

cape4

The results are rather clear, excepting the difference between the MDS and admixture estimates which seem to place less weight on the Bantu component in the second than the former. The authors chalk this up to difficulties distinguishing the Khoisan from the “pan-African” component. Contemporary Khoisan show substantial overlap with Bantu groups (just as some Bantu groups in South Africa such as the Xhosa show a great deal of Khoisan ancestry), so there are some ambiguities in assigning a haplogroup to one population or the other (the overlap seems a product of recent admixture).

But be as that may be, it is clear that a major dynamic in the founding of the Cape Coloureds had to be the pairing of Khoisan females with non-Khoisan males. The disjunction between European ancestry on the male and female lineages is stark, but should not be surprising in light of what we know from colonial history. And perhaps not just the colonial history of South Africa. The same pattern is evident in Latin America. Even societies which have transitioned from Mestizo to white, such as Argentina, seem to have done so through generations of male biased migration so that the indigenous mtDNA remains. And the same pattern can be found in some cases where we have no historical documentation because ethnogenesis occurred during the prehistorical period. In particular this seems the case in India, where male lineages show a strong West Eurasian bias, while female lineages do not (they are more closely related to East Eurasian lineages, though that connection is much more distant than Indian West Eurasia lineages have with other West Eurasian lineages).

A little over 10 years ago L. L. Cavalli-Sforza was coauthor on a paper titled Genetic evidence for a higher female migration rate in humans. The logic behind the results are simple, most human societies are patrilocal, so one presumes that gene flow would be mediated by the movement of women between local groups. Cavalli-Sforza found that female lineages seemed to be less localized than male lineages, implying greater gene flow. The literature since then seems rather muddled, and has not confirmed this original finding in a solid manner. I suspect that this is because one general dynamic can not capture the varied events which have characterized human genetic history. That is, there were periodic “shocks” to the basic patterns of worldwide genetic variation, but after those shocks passed then the dynamics which Cavalli-Sforza saw would come to the fore. Exploring the details of the balance between these varied forces is going to be where the future avenues of research lay. I predict that it is going to be in regions and populations which have gone through great cultural ferment since the last Ice Age that you will see this palimpsest whereby variation emerged as a synthesis of shocks interleaved between long periods of stasis and more conventional deme-to-deme gene flow. By contrast, isolated hunter-gatherer populations such as the Andaman Islanders may have missed out on the shocks, the period of “genetic revolutions” (though as I imply above, most hunter-gatherer populations show a great deal of admixture with the far more numerous agricultures who marginalize them and push up against their range, as is in the case among the Bushmen).

Finally, going back to South Africa one major issue is going to be the nature of the Afrikaners. Tentative earlier genetic and genealogical work suggests that ~5% of their ancestry is non-European, probably reflecting the movement of Cape Coloureds who could pass as white into the Afrikaner population (Cape Coloureds usually share language and religion with Afrikaners, so the cultural move would not have been insurmountable). Yet I have seen very few papers such as this, Deconstructing Jaco: genetic heritage of an Afrikaner. The author concludes that ~6% of his ancestry is from non-white slaves, in line with prior expectations. Though white Americans often take pride in their Native American ancestry (often genealogically attested, as with the descendants of Pocahontas) the total proportions are actually rather small, probably on the order of ~1% at most. In contrast the Afrikaners likely have more non-white ancestry because their founding population did not receive as much migration from Europe to dilute the original non-European element.

Addendum: The Cape Coloureds seem a real interesting population in light of admixture mapping, no?

Citation: Quintana-Murci, L., Harmant, C., Quach, H., Balanovsky, O., Zaporozhchenko, V., Bormans, C., van Helden, P., Hoal, E., & Behar, D. (2010). Strong Maternal Khoisan Contribution to the South African Coloured Population: A Case of Gender-Biased Admixture The American Journal of Human Genetics, 86 (4), 611-620 DOI: 10.1016/j.ajhg.2010.02.014

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Cape Coloureds, Culture, Genetics, South Africa 
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Razib Khan
About Razib Khan

"I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. If you want to know more, see the links at http://www.razib.com"