Mostly, it isn’t.
But there is a sign of a disturbing history deep in the genetic heritage of most Puerto Ricans. And contrary to the popular belief, there may be some trace of the same history in Argentina.
Some background. Over on Twitter, the great Pseudoerasmus and the great Gabriel Mathy began a debate over why North America saw relatively little intermarriage between Europeans and Native Americans compared to elsewhere. Pseudoerasmus argued that it was all about initial conditions. The Iberians migrated in smaller numbers to areas with bigger indigenous populations and in a heavily male-heavy environment. Gabe, conversely, argued that it was all about cultural norms. The English did not intermarry in significant numbers even in places with high numbers of indigenous and skewed sex ratios.
It was an interesting discussion which I hope is put into a blog post. I participated for a bit but dropped out; Pseudoerasmus and I get along brilliantly, but in the heat of tweeting innocent responses can come across as more than slightly hostile. Moreover, the long threads are impossible to follow, quite unlike comment threads on a blog or the old newsgroups. (or ... gulp ... Reddit.) These are two of the reasons why I think Twitter is useless (at least for me) and am leaning towards quitting the platform, but I digress. If you must, try here and here.
What does any of this have to do with Puerto Rico? Well, early DNA studies, from back when such things were new and neat, showed something a bit creepy. Mitochondrial DNA (mtDNA), which is passed down through the female line, skewed Native American. But Y-chromosomes were entirely European and African. The implication is that something awful happened to the entire male Taino population; they were either killed or denied the possibility of procreation. Likely both.
Later studies upheld the results. Here is one from 2014, which sampled 326 people and found mtDNA that was 60% indigenous, 25% African, and 15% European, whereas the male Y-chromosomes were 85% European and 15% African.
Argentina is typically thought of as a European settler offshoot, and with good reason. In 1895, 25% of the population was foreign-born, overwhelmingly from Europe and the Levant. By 1914, that figure was up to 30%. Gross immigration between 1857 and 1914 came to 4.6 million people; net immigration ran about 3.0 million. (Pages 201-02 of the 1914 census.) All this with a population of only 7.9 million in 1914! Add in the Argentine-born children of those 3.0 million post-1857 immigrants, and you have a veritable transformation of the population. You might reasonably expect Argentines to have a similar genetic makeup to, say, white people in the northeastern United States or Ontario.
But there is some evidence that you would be wrong.
A 2010 study found that 54% of Argentine mtDNA came from indigenous sources while 94% of Y-chromosomes traved to Europe. These results are strikingly close to Puerto Rico (minus the large African admixture on the island) ... shockingly so for a country which received mass immigration from Europe in relatively recent times.
So what explains the result?
Well, first, maybe it is wrong. It is one study of 246 individuals and sampling issues are not small. I suspect that the prevalence of indigenous mtDNA it is more-or-less correct; the result has been corroborated in multiple studies. The Y-chromosome part is dicier.
Second, another study added a wrinkle: half of the indigenous South American DNA appears to have originated outside the modern borders of Argentina. That opens up the possibility that at least half of the result may be driven by migration from Paraguay, Bolivia, and Peru. As the authors write, “We did not collect bio-geographic information for most of the donors of our samples, and this is information was not available for most of the data collected from the literature; therefore, some donors could be in reality Native American immigrants (or descents form parents) from neighboring countries.”
Finally, European immigration to Argentina skewed male. (See page 271; it goes to CICRED 1974.) In 1869-1914, 1.7 males arrived for every female. That could explain some of the disproportionate prevalence of European Y-chromosomes compared to mtDNA without the specter of a Puerto Rican style past holocaust.
Nonetheless, the prevalence of native American ancestry in Argentina — and its apparent concentration in maternal ancestral lines — is a bit of surprise! There is a lot we do not know about the Argentine past ...