Studies investigating evolutionary theories on the origins of national differences in intelligence have been criticized on the basis that both national cognitive ability measures and supposedly evolutionarily informative proxies (such as latitude and climate) are confounded with general developmental status. In this study 14 Y chromosomal haplogroups (N = 47 countries) are employed as evolutionary markers. These are (most probably) not intelligence coding genes, but proxies of evolutionary development with potential relevance to cognitive ability. Correlations and regression analyses with a general developmental indicator (HDI) revealed that seven haplogroups were empirically important predictors of national cognitive ability (I, R1a, R1b, N, J1, E, T[+L]). Based on their evolutionary meaning and correlation with cognitive ability these haplogroups were grouped into two sets. Combined, they accounted in a regression and path analyses for 32–51% of the variance in national intelligence relative to the developmental indicator (35–58%). This pattern was replicated internationally with further controls (e.g. latitude, spatial autocorrelation etc.) and at the regional level in two independent samples (within Italy and Spain). These findings, using a conservative estimate of evolutionary influences, provide support for a mixed influence on national cognitive ability stemming from both current environmental and past environmental (evolutionary) factors.The association with cognitive ability is positive for haplogroups I, R1a, R1b, and N and negative for J1, E, and T[+L], a pattern that also holds within Spain and Italy.
I1 arose in southern Scandinavia between 4000 and 6000 years ago (Rootsi et al., 2004). R1a and R1b arose in southwestern Asia (Caucasus, Pontic–Caspian steppe, Kurgan culture) around 22,000 ybp or somewhat later at 18,500 ybp. N and its relevant European subclades arose in Siberia and central Asia 12–27,000 ybp (Rootsi et al., 2007). This suggests that these environments may have been evolutionarily significant for cognitive ability: The presence of environmental harshness (i.e. extreme winter cold) suggests that factors relevant to the cold winters theory could have contributed to an increase in intelligence among the ancestors of those possessing these haplogroups. It is also likely that factors such as the development of agriculture, tools and dairy farming (milk from horses and cattle around 6000 ybp) were themselves an evolutionary catalyst for increasing cognitive ability (Cochran & Harpending, 2009; Hawks, Wang, Cochran, Harpending, & Moyzis, 2007; Wade, 2006), possibly enhancing neurological maturation via the provision of better nutrition during pregnancy, in youth and adulthood. The Neolithic transition to agriculture in cold climates would have been particularly evolutionarily demanding in terms of the need for heightened cognitive resources (e.g. farsightedness and planning).
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Finally the steppe presents an unprotected environment, people living in such an environment are different to the people living in mountains, near to large oceans, in dense forests or in oases surrounded by large deserts, as they are permanently in danger of being attacked by neighboring peoples. This challenge could have selected for enhanced military preparedness a component of which may have been higher cognitive ability.