Previously, a literature review was conducted regarding continental racial admixture and educational attainment and/or socioeconomic status. Across the Americas, Amerindian and African (versus European) ancestry was found to be negatively correlated in admixed populations (e.g., Hispanic Americans) with income, educational attainment, occupational rank, and other cognitively correlated indexes of socioeconomic status. Multiple possible explanations were discussed. Some of these predict that the ancestry-outcome association will generalize spatially, such that admixture will be correlated with outcomes across regions and nations. This need not be the case and is not directly predicted by other accounts of the individual level admixture-outcome associations, such as phenotypic based discrimination ones, which work on the individual-level. The association between regional ancestral and cognitive related outcome variation in Mexico will first be explored, since for this county reliable regional admixture estimates, at least with regards to European and Amerindian ancestry, and outcome measures are available and also since there is a good deal of spatial variation in admixture (and outcomes). Subsequently, the analysis will be generalized to the whole of the Americas. The Figure 1 below depicts the Mexican spatial ancestral racial variation.
Method: Admixture estimates: Admixture estimates were taken from Salzano and Sans (2014) and Moreno-Estrada et al. (2014). For the two sources, Pearson correlation was 0.94 for European admixture, -0.60 for African Admixture, and 0.94 for Amerindian admixture. Regarding European and Amerindian admixture, the estimates exhibited a high reliability, thus justifying their combination. The African Admixture estimates were unreliable due to the noisiness of the measures in conjunction with the limited range and variance in admixture. Admixture estimates were averaged for each district. Missing district data was then estimated based on the measured admixture of adjacent regions. This produced four different admixture estimates: (a) Salzano and Sans (2014), (b) Moreno-Estrada et al. (2014), (c) the average of (a) and (b), and (d) estimates based on (c) taking into account regional proximity. Descriptives are presented in Table 1. Cognitive Ability estimates: 2003, 2006, 2009, and 2012 average math and reading PISA scores were computed for each district. Regional scores were highly correlated across years, thus justifying the use of cross year average scores; deviation scores relative to the Mexican national mean were computed and averaged across years. 2002 and 2005 average district level Raven’s Matrices scores were also computed. Human Development Index: 2010 and 2012 Human Development Index scores highly correlated across year. And average scores was computed. The excel data file is attached.
Results: Since % African estimates were unreliable, these were treated as noise and this noise was partialed out in the correlation analyses. Thus, for these analyses the total ancestry was the Amerindian + European ancestry. The correlations between district level Amerindian Ancestry (with and without estimates) and district level cognitive ability and human development are shown below. Percent Amerindian Admixture was a strong negative predictor of district level outcomes. Partailing out the noisy African Admixture didn’t have a substantive effect on the correlations. Correlations using estimated and measured only admixture were similar as were ones using averaged admixture estimates and those provided by Salzano and Sans (2014) and Moreno-Estrada et al. (2014) independently. Results are shown in Table 2. The regression plot showing district level admixture (without African ancestry partailed out) and district level cognitive scores is shown in Figure 2. District level cognitive ability substantially mediated the association between continental ancestry and HDI (with and without African ancestry controlled for). (Without African admixture controlled for: Pearson correlation (AmerAdmix x HDI) = -0.603; AmerAdmix x HDI) correlation with PISA scores partailed out: -0.271.)
Discussion: Regional Amerindian Admixture was a robust predictor of regional outcome differences. The Amerindian ancestry -outcome association found based on admixture mapping generalizes spatially, at least in Mexico. These findings are as would be predicted by an evolutionary genetic explanation. Variations of shared environmental — “cultural” — accounts are possible insofar as shared environment can be genealogically sticky.
Tables and Figures: