I was thinking to title this post El Día de la Raza (The Day of the Race), as Oct 12 is still called in some countries, but it'd need too give many explanations that I will deliver anyhow but in the article's body. The word race here has nothing to do with people, animals or cars running competitively but with ethnography: stock. However it is a very Latin understanding of the concept of race as ethno-linguistic and not truly biological reality, so it makes total sense... if you are from a Latin culture.
After all, what the Germanics (wrongly) think as races are nothing but residual peripheral popuations of the only true mestizo human (and Spanish-speaking) race... or something like that. A good example, as good as any other, I guess, are Costa Ricans.
Zhaoming Wang et al., Genetic Admixture and Population Substructure in Guanacaste Costa Rica. PLoS ONE 2010. Open Access.
As usual in this type of papers, they estimate the tricontinental admixture in Costa Ricans of Guanacaste Province (NW Costa Rica, bordering Nicaragua).
The results show that this Central American population can well be described on average as 43% European, 42% Native American (38% NA+ 4% East Asian components) and 15% African by ancestry. Individual apportions and even local averages may vary somewhat but that is about it:
|Eigenvector analysis with some localities (fig. 6)
None of the individuals sampled clusters too tightly with either reference "purebreed" HapMap samples. However in the Structure analysis (below) you can see maybe more clearly that a few (not too many anyhow) do not seem to have any African ancestry and that individual admixture ratios vary somewhat, of course.
|STRUCTURE analysis (k=4)
Somewhat anecdotally they talk about a subpopulation that would be closer to genuine Europeans (60%) but I don't think the case is very clear, just tendencies within a continuum. The perfect cladistic scenario in fact.