Economists in the last few years have been shifting toward testing their theoretical models, whether through the experiments of behavioral economics, or, “natural experiments.” The reason economists have had issues with testing their models is that experimentation on humans has some natural constraints. Macroeconomists have an even greater problem, as experimentation on whole societies not only presents ethical conundrums, but there’s no way to fund or implement experiments on this scale. Macroeconomists turn out to be the paleontologists of economics.
Of course economists aren’t the only ones who’ve had this sort of problem with humans. The reason that geneticists focused on organisms such as flies, mice and fish is partly that these taxa breed fast and are easy to maintain in laboratories. But obviously there are things you can do, such as mutagenesis, with model organisms which you can not do with humans. Human genetics has traditionally relied on “natural experiments” of a sort, inbred lineages, recurrent recessive diseases, etc. Genetics has been a supplementary handmaid to medicine by and large. But sometimes history can load the die in genetics’ favor as well.
During the “Columbian Exchange” the New and Old World engaged in a massive transfer of ideas and individuals. The Old World received potatoes, maize, and tomatoes (to name a few). The New World…well, the New World received black people and white people. As documented in works such as 1491 the indigenous populations of the New World collapsed with the introduction of Old World diseases. Native peoples disappeared from the Caribbean, and were marginalized on the mainland excepting ecologically remote (e.g., the Guatemalan highlands) or forbidding (e.g., the Peruvian highlands) regions. But of course despite the obliteration of indigenous cultural self-consciousness and identity, the native populations did not totally disappear, they persisted genetically in the numerically dominant mestizo populations of much of Latin America. You don’t need genetics to understand what happened, books like Mestizaje in Ibero-America outline in detail using conventional historical archives how Spanish men arrived in New World and entered into relationships with indigenous women. Often several at a time, in contravention of the Catholic Church’s requirement of monogamy.
But in the post-genomic era we have more to go on than impressions, we can quantitize the extent and nature of the admixture, something of importance when considering medical research. A new paper in PNAS adds some more to the growing body of results on Latin American genomics by including populations which have traditionally been overlooked, and also putting a spotlight on the long term impact of sex-biased admixture. Genome-wide patterns of population structure and admixture among Hispanic/Latino populations: