Significant cultural and physical differences ... the stuff of race and ethnicity ... are prominent when people move across continents or between them. Eventually, the ponderous events of history, which involve occasional foldings in the continuum of human variation, causing apparent patchiness, are offset by the frequent events of human activities, resulting in genetic and cultural admixtures. What colonialism, invasion, and migration do is undone.
A new study out in PLoS Genetics examines this phenomenon for Latin America, with a study of genetic admixture.
From the Author's Summary:
The history of Latin America has entailed a complex process of population mixture between Native and recent immigrants across a vast geographic region. Few details are known about this process or about how it has shaped the genetic makeup of contemporary Latin American populations. To perform a broad exploration of the genetic diversity of Latin America we carried out genome-wide analyses in 13 mestizo populations sampled from 7 countries across the region. We observe a marked variation in ancestry both within and between mestizo populations. This variation in ancestry correlates with pre-Columbian Native population density in the areas examined and with recent patterns of demographic growth of the sites sampled. We also find evidence that the mixture at the origin of these populations involved mainly immigrant European men and Native and African women. Finally, mestizo populations show a differentiated Amerindian genetic background, consistent with a predominantly local Native ancestry. Mestizos thus still reveal the genetic imprint of the pre-Columbian Native American population diversification. Our study helps delineate the genetic landscape of Latin America and has a number of implications for gene identification analyses in populations from the region.
So this study reveals, or at least conforms to expectations of, the practice of hyergyny, whereby men of a "dominant" culture and the women of the invaded or colonized culture interbreed, with the gender-reversed scenario being rare. In this case, the cultures preferentially contributing females to this admixture included both native and immigrant African groups.
Also indicated is a genetic and linguistic "bleed through" of pre-colonial distributions of people, despite the geographically broad and powerful effects of conquest and colonization.
In conclusion, this initial genome-wide analysis of admixture across Latin America has revealed a hitherto undetected differentiation of the Native American ancestry in Mestizos. This fact, together with the extensive variation observed in rates of admixture across populations, and sometimes also between individuals within populations, needs to be considered when designing admixture mapping studies in specific Latin American populations. Despite these complications, we anticipate that admixture mapping in Mestizos should prove a fruitful strategy for analyzing the genetic basis of phenotypic traits, including disease, differing between Native Americans and Europeans.
Wang, S., Ray, N., Rojas, W., Parra, M.V., Bedoya, G., Gallo, C., Poletti, G., Mazzotti, G., Hill, K., Hurtado, A.M., Camrena, B., Nicolini, H., Klitz, W., Barrantes, R., Molina, J.A., Freimer, N.B., Bortolini, M.C., Salzano, F.M., Petzl-Erler, M.L., Tsuneto, L.T., Dipierri, J.E., Alfaro, E.L., Bailliet, G., Bianchi, N.O., Llop, E., Rothhammer, F., Excoffier, L., Ruiz-Linares, A., McVean, G. (2008). Geographic Patterns of Genome Admixture in Latin American Mestizos. PLoS Genetics, 4(3), e1000037. DOI: 10.1371/journal.pgen.1000037