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Mixed-Race

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I have long had a problem with projections of the racial makeup of the USA which implicitly neglect the complexities inherent in the identity of someone of mixed origin. A new study analyzing Census data on interracial marriages between 1980 and 2008 highlights some of the subtleties:

The study also examined trends in biracial and cohabiting Americans.

The study found that people who classified themselves as white-Asian or white-American Indian were more likely to marry whites than Asians or American Indians.

“The rise in America’s multiracial population blurs racial boundaries,” Lichter said.

However, black-white biracial people are still more likely to marry blacks than whites.

First, the simplest way to state the implications of these data is that whites are becoming more Asian and American Indian, while blacks are becoming whiter. At least in terms of ancestry if not identity.

Consider the case of the actor Dean Cain, born Dean Tanaka. His paternal grandfather was of Japanese ancestry. He has a son with ex-girlfriend Samantha Torres. She happens to be a blonde and blue-eyed Spanish model. By the cultural norms of hypodescent Christopher Dean Cain is not a non-Hispanic white. If you have too many people who “look white” but have non-European ancestry hypodescent is not feasible. That was not the case for the United States of America for most of its history. But by 2050 the situation may be very different, and the cultural landscape of race and ethnicity may be very different.* I suspect that many of the assumptions we make about the world of 2050 by naively projecting out growth rates and the cultural mores of 2010 are going to fall into the “not even wrong” category.

* In many Latin American nations it is obviously not the case that mestizos make common cause with indigenous people against white elites as “people of color.”

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Anthropology, Census, Culture, Hypodescent, Mixed-Race 
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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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adriana-limaA few months ago I was thinking a fair amount about the Neandertals. One issue which became more stark to me due to that particular finding, that a few percent of the human genome seems to have derived from Neandertal populations, is the reality that genetic distinctiveness can persist long after cultural coherency is no longer a reality. That made me reconsider one of the facts of contemporary scholarship, that the Amerindian populations of the two most populous nations of the New World, the United States of America and Brazil, have disappeared or been totally marginalized demographically.

I’ve observed before it looks like that about 15-20% of the ancestry of the Argentine population is Amerindian, despite the nation’s proud identity as a European settler offshoot (i.e., more like the United States or Australia, than Mexico, which has an explicit hybrid identity). But I realized that Brazil was perhaps the bigger catch.

Only 0.4% of Brazilians identify as Amerindian. That’s about 700,000 people. But we know that a substantial number of white, brown and black Brazilians have Amerindian ancestry. Assuming for argument’s sake that the 700,000 Amerindians have undiluted indigenous ancestry, how much of the distinctive Amerindian genome in modern Brazil is to be found in this segment of the population?

There was a paper which came out in an obscure Brazilian journal last year which can help answer this question, DNA tests probe the genomic ancestry of Brazilians. For the purposes of the paper they needed to find a small number of ancestrally informative markers which would allow them to partition the ancestries of the individuals in their data set into European, African, and Amerindian, segments. Luckily these are three very distinctive populations. They cross-checked the utility of their markers against the HGDP data set. In other words the precision and accuracy of the 40 markers they selected should be assessed by how well they can distinguish these three “pure” populations. Their Brazilian subjects consisted of self-identified whites from various regions, as well as black men from Sao Paulo. Brazil’s racial taxonomy has a brown (pardo) category which is large, but judging from the very high proportion of African ancestry among the blacks in their sample I don’t think they included self-identified mixed-race people in that group (some scholars lump mixed and black Brazilians together into the black category).

First, let’s see how well the markers allow for us to distinguish populations’ whose ancestry we’re pretty sure about.

7913i02

No that bad. Observe the trailing off of Europeans and Amerindians along their axis of variation. From previous papers using SNP chips with hundreds of thousands of markers It seems that the HGDP Amerindian sample has non-trivial European ancestry, so it isn’t just a limitation of their marker set. This shouldn’t be that surprising in light of the history of Latin America, and the centuries of racial fluidity which occurred. Additionally, I assume that it would be more difficult to find markers which vary between Europeans and Amerindians than between these two groups and Africans (remember that Africans have more genetic diversity, and non-African populations can be thought of as simply one branch out of Africa).

The following chart shows the outcome from the markers across various regions of Brazil. I assume that the core American readership will be pretty ignorant of the regions, so this map will help. Southern Brazil is white. The rest of the country far less so. Gisele Bündchen and Alessandra Ambrosio are from Rio Grande do Sul in the far south. Adrianna Lima, pictured above, is from Bahia in the northeast. All of the panels are for whites (through self-identification) except for the last.

7913i03

Despite the limitations of 40 markers I think the results here are probably pretty good. The South region has the whitest whites. This was an area with massive immigration, and fewer non-whites to start with. It is in the northeastern region that you see more Amerindian than black ancestry among the whites. From what I have seen in other papers the brown category in Brazil is more skewed toward European ancestry than panel F, so that’s why I assume that these are men who self-identify as black.

But for the purposes of my original question we need to assess ancestral contributions within these groups from Amerindians. The following table does just that.

7913t01

The authors note a curious fact: there’s no statistically significant difference between the regions in terms of Amerindian ancestry for self-identified white Brazilians. This resembles the pattern we saw with Neandertal admixture, and I assume the explanation is the same: the integration of Amerindian ancestry occurred early in the history of the white Brazilian population and has now distributed throughout it via generations of intermarriage except for those with undiluted white immigrant heritage (e.g., Gisele, who comes from a German town). The figure for blacks from Sao Paulo is about the same as whites as well.

Let’s assume 10% Amerindian ancestry and 200 million Brazilians to make the math easier. Since it is about 10% in whites and blacks, I suspect it will be 10% in those who identify as mixed race as well. Where does that leave us? That would mean 20 million Brazilians of Amerindian ancestry! As you can see around 95% of the Amerindian genome in Brazil is found among those who do not self-identify as Amerindian.

For Americans (citizens of the USA) it is then interesting to wonder how much of the Native genome is found in whites, particularly old stock colonial descended whites, and how much in self-identified Native Americans. Looking at the genetic studies I believe that the Amerindian proportion is much lower among white Americans than 10%. Additionally, while 700,000 Brazilians identify as Amerindian, 2.4 million Americans do (though I believe that a much larger proportion of American Native Americans are of mixed ancestry than Brazilian Aboriginals). I think that the odds are that more ancestry which is pre-Columbian in the USA does reside within the white population than within the self-identified Native American tribes, but it may be a close thing. And of course there are Latino populations which need to be added into the equation, whose Amerindian ancestry is significant (in the case of Mexican Americans possibly preponderant), though it is of Mesoamerican origin.

But doing those sums is for another post.

Note: A preemptive apology to those who feel I’ve used the wrong term for any particular ethnic group. I have preferred the more Politically Correct (though less popular) term Native American in the context of the USA, but feel that Amerindian is technical or scholarly enough to evade charges of insensitivity.

Image credit: UnaFraseCelebre.com

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Brazil, Culture, Genetics, Genomics, Mixed-Race 
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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"