Recently I was pointed to an article titled Multiracial patients have tough battle to find marrow matches in USA Today. This is an issue that I was aware of, I recall reading about a young girl of Thai and European American background who travelled to her mother's homeland to look for a tissue match among that nation's rather large (in comparison to the United States) Thai-European mixed community. My post from yesterday should have made the tissue rejection quandry that mixed-race individuals might face rather clear, if their parents pass on to them combinations of alleles which are disjoint between their subpopulations (that is, present in one, but not present in another) then their own HLA profile might be very rare indeed. As someone who is quite possibly going to have children of mixed genetic background on a transcontinental scale, I have given some thought to this issue. Noting the prominence of the mention of HLA frequency differences on some racialist sites, I also know that some who argue against miscegenation bring this point up as well.

Science can be drafted in the service of many viewpoints. Tissue incompabilities are a salient fact of life. There is also some possibility that miscarriage rates are heightened when there is a sharp immune incompability between mother and fetus. Clearly there is a limit to any benefit that one might receive from antigen profile similarity, otherwise we would preferentially mate with our siblings and likely resemble cheetahs, who are so inbred that one can perform grafts without any worry.

But, if one can posit the downsides in the realm of possible organ failure, why not wonder about the possible benefits of novel heterozygosity or rare phenotype? After all, there is a reason that the HLA loci are so polymorphic! Additionally, focusing on interpopulational differences obscures a crucial point that many HLA alleles seem to be transpecies, in other words, your HLA profile might more closely resemble a Chimpanzee in Gabon than your cousin (this is admittedly a far fetched comparison, but the fact that it is not outside the domain of possibility should give one pause). In the short term, one could wonder if mixed-race children might be less susceptible to diseases endemic in more numerous populations, and in the long term, perhaps they would be more likely to survive any future "superplague."¹

In the end I must admit that such considerations are not ones I give a great deal of thought too. I read multiracial sites on occassion and some of the activists in this movement do talk about hybrid vigor and what not, but it is clear that these issuses are secondary and not contributors to their boosterism of miscegenation. Similarly, it seems to me that those who promote same-ethnicity mating as a normative value and bring up opposing talking points to the ones above also consider these ancillary to their ultimate aims. Biological points, from where I stand, are definitely trival in comparison to a personal worldview shaped by proximate experiences and values.² The science is fuzzy and flexible enough that you can generally extract some "natural" justification for your given normative position. Biology is more useful I suspect in clarifying the plausible paths of implementation, and the obstacles one needs to surmount, via a canalization effect (constraining your public policy prescriptions into the lowest possible of the alternative channels). It still leaves room in the end for a variety of terminal positions.

This is why I get rather frustrated with those who are ostentatiously anti-ethnocentric and those who are racial/tribalist in orientation when they present biological talking points as if they quite transparently support their own stance. Uninterested in the particular details and nuances they generally garble proximate and ultimate, issues of is and ought, and seem to have only a minimal interest in a model of the world as it is when set in all its particular subtle detail next to their own broad-brush vision of what it should be. The temptation to sample bias theoretical points while ignoring others is just too great for mortal men, alas.

Addendum: I have mentioned the high Rh- frequency of the Basques before. This is one quite clear pre-modern reproductive barrier between human populations. The high frequency of Rh- among the Basques, and the reduced fertility of Rh+ males & Rh- female matings, would serve as a asymmetrical barrier to Rh+ genes as opposed to other loci. In other words, if two non-Basque males entered a Basque community, and one was Rh- negative (10-15% of Europeans are), while the other was Rh+, then "non-Basque" alleles could enter the Basque population via Rh- non-Basque males (or to a lesser extent, heterozygous Rh+ males).

Additionally, this might be a case where one could explore a putative model where fecundity/viability barriers between populations might result in selection for different proximate traits. In other words, I am suggesting that Rh- women who preferred "Basque looking men" should be more fecund than women who did not, because the latter were more likely to marry non-Basques and therefore Rh+ men.

In the case of the Basques, I have not seen any great preferences of Basque females toward a particular phenotype (I lived in a part of the country with a rather large Basque community). There might still be sexual selective biases, but they don't seem to be extremely strong. But the "sickliness" of Basques during pregnancy was noted in the pre-modern era, so it seems plausible that natural selection could have shaped in their preferences.

My moderate experience with non-Basque people of Spanish origin (that is, natives of Spain, not Latin America) is that the two subsets intersect a great a deal in "look & feel." In contrast, along much of the east and north of India there is a far sharper phenotypic cline which runs along an altitude barrier above which lowland South Asian agricultural practices are no longer appropriate, and where Mongoloid populations practice a montane lifestyle. In this case there is no obvious biological fecundity barrier that I know of (both populations are nearly 100% Rh+ for example), instead, geographic realities in concert with cultural differences have enforced a genetic barrier so that distinct phenotypes are maintained (though if you know any Nepalese you will notice that even "Indo-Aryan" high caste individuals often have a somewhat Mongoloid appearence in comparison to people from the Gangetic plain). To me, this puts in perspective the relative importance of biology set next to geography and culture when it comes to intermarriage between groups.

1 - In the case of individuals, outmarriage might be very "rational" on a genetic level. Think of the Andaman Islanders, it seems that they have little immunity to high density bred pathogens which Indian mainlanders bring with them. Even if an Andaman Islander takes a personal health risk in mating with an Indian, it might be his/her best chance of having descendents in the long term since their line needs an infusion of alleles which grant them some level of resistance to density born & bred pathogens.

2 - Obviously your biological background has a very important role in shaping your experiences and to some extent even your values! But these inputs are far upstream of the opinions and behaviors one manifests, and the way they map and transform themselves is not, at least to me, as clear as some would assert. And of course, quite often on the individual level they are less than illuminating, as opposed to the populational level where broad patterns are quite clearly discernable.