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Health

Genetics, the myth-buster? The case of Argentina

Gene ExpressionBy Razib KhanMarch 8, 2008 12:25 AM

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As I have noted before one of the consequences of genomic analysis techniques becoming relatively cheap and accessible is that they are now viable tools toward exploring a host of fundamentally non-genetic questions. That is, instead of exploring the dynamics of evolutionary biology, they can be used to shed light upon other sorts of dynamics. Sometimes the questions are fuzzy and the techniques can be laborious; e.g., the extraction and analysis of ancient DNA and their subsequent insertion into an explanatory framework where the non-genetic data are patchy. On other occasions, the interpretations are easier. Consider the demographics of Argentina:

Argentina is a melting pot of different peoples, both autochthonous and immigrants. Citizens of European descent make up the great majority of the population, with estimates varying from white 89.7% to 97% of the total population. The last national census, based on self-ascription, indicated a similar figure.

As a point of comparison, the United States of America is 74% white in terms of self-identified race. In other words, Argentina is a nation with a self-perception of more European ancestry than that of the United States! Argentines consider themselves to be a fundamentally European derived people, in other words, they're a settler society like the United States, Australia or New Zealand. This is in contrast to the melting-point mythologies which are dominant in places such as Mexico or, a lesser extent, Brazil.^1 But what do the genes say? Well:

A study conducted by Argentine, Swedish and North American institutions, established that the genetic average structure of the Argentine population, contains 79.9% of European contribution, whereas the Amerindian admixture, though not fully visible in physical appearance, was estimated to be present in a high percentage of the population, close to 56% on either paternal or maternal lineages, of which just 10% were shown to have Amerindian ancestors on both lineages.

This study, Argentine population genetic structure: large variance in Amerindian contribution, has more detail:

Argentine population genetic structure was examined using a set of 78 ancestry informative markers (AIMs) to assess the contributions of European, Amerindian, and African ancestry in 94 individuals members of this population. Using the Bayesian clustering algorithm STRUCTURE,

the mean European contribution was 78%, the Amerindian contribution was 19.4%, and the African contribution was 2.5%.

Similar results were found using weighted least mean square method: European, 80.2%; Amerindian, 18.1%; and African, 1.7%. Consistent with previous studies the current results showed very few individuals (four of 94) with greater than 10% African admixture. Notably, when individual admixture was examined, the Amerindian and European admixture showed a very large variance and individual Amerindian contribution ranged from 1.5 to 84.5% in the 94 individual Argentine subjects. These results indicate that admixture must be considered when clinical epidemiology or case control genetic analyses are studied in this population. Moreover, the current study provides a set of informative SNPs that can be used to ascertain or control for this potentially hidden stratification. In addition, the large variance in admixture proportions in individual Argentine subjects shown by this study suggests that this population is appropriate for future admixture mapping studies.

Additionally, as in most Latin American populations, the admixture exhibits a strong sex bias, it seems that maternal lineages (mtDNA) are much more Amerindian than paternal (Y) lineages. The results above use autosomal markers, that is, examining points across the whole genome, so it is not surprising that the Amerindian fraction is far lower than what mtDNA would show. So what does the genetics tell us in combination with the social data? Individuals will admit or identify to non-European ancestry only when it is visible, because white identity is normatively preferred (in the United States the proportion claiming Native American ancestry has increased in direct relation to the rehabilitation and romanticization of Native people).^1 If one assumes that only with an ancestral proportion around 1/3 can one not deny non-European ancestry (at least on average), then the vast majority of Argentines with a significant proportion of non-European ancestry (on the order of 5% or greater) could likely pass as white.^2 The bigger picture of what this tells us is that identity is a synthesis of various factors. The Argentine identity is shaped by social considerations; the self-perception that Argentina is a European society, the tacit assumption that to be white is to be a normal Argentine, and so forth. But these preferences and social dynamics lay atop genetic realities mediated through phenotypic perceptions. In plain English, if Argentina had a more balanced Amerindian and European genetic contribution a straightforward self-image as a European settle society would be implausible, too many characteristics which would identify a strong non-European genetic ancestral component would be extant within the population. As it is, since Argentines are mostly European in ancestry the non-European signal, which is easily discernible at the genetic level, is also easily masked. This is a function of the way our cognitive engine interprets traits and engages in categorization. Genetic inheritance is a discrete process, DNA information is encoded along base pairs, but because of the incredible number of points we naturally tend to engage in a blending fallacy in our everyday relations. In terms of phenotype our classes are coarse, and instead of engaging in some sort of complex statistical inference we simply utilize rough & ready heuristics. We bin people into their categories, and we reconceptualize any more finely graded variation to conform to our small set of distinct classes. 1 - Immigrant groups such as Germans and Japanese seem to have preserved a greater amount of cultural distinctiveness in Brazil than in Mexico, where a mestizo identity is dominant even though the conventional racial caste system with Europeans on top, mestizos in the middle and the Indians on the bottom still persists nevertheless. 2 - The conflation between white and European here is problematic. Though most Argentines are of Italian, Spanish or Northern European ancestry, a significant minority of Arabs exists. In fact, there was a recent president of Syrian ancestry. Since Levantine Arabs can usually pass as Southern European I don't think that they would be assumed to be non-white, though their "Turkish" identity is noted in most Latin American countries (both Shakira and Salma Hayek have Arab ancestry).

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