On the Nature and Nurture of Intelligence and Specific Cognitive Abilities

Abstract

To further knowledge concerning the nature and nurture of intelligence, we scrutinized how heritability coefficients vary across specific cognitive abilities both theoretically and empirically. Data from 23 twin studies (combined N = 7,852) showed that (a) in adult samples, culture-loaded subtests tend to demonstrate greater heritability coefficients than do culture-reduced subtests; and (b) in samples of both adults and children, a subtest's proportion of variance shared with general intelligence is a function of its cultural load. These findings require an explanation because they do not follow from mainstream theories of intelligence. The findings are consistent with our hypothesis that heritability coefficients differ across cognitive abilities as a result of differences in the contribution of genotype-environment covariance. The counterintuitive finding that the most heritable abilities are the most culture-dependent abilities sheds a new light on the long-standing nature-nurture debate of intelligence.

Mothers-Offspring Resemblance in Intelligence and Its Relationship to Socioeconomic Status

“…Thus, h 2 of fluid intelligence should be higher than crystallized intelligence. However, our results are consistent with Kan et al (2013) who observed the same surprising result after analyzing 23 twin studies (N = 7,852). These authors found that the heritability coefficients of culture-loaded tests (crystallized measures) tended to be larger than those of culture-reduced tests (fluid measures).…”

“…Moreover, a meta-analysis recently conducted by Pietschnig and Voracek (2015) of trajectories of the Flynn effect across cognitive abilities, from 1909 to 2013, indicated strongest gains for Gf than Gc, which in some way could be linked to the study of Kan et al (2013), and to our present study. These last two studies found more heritability for Gc than Gf, which implies that cognitive gains through generations can be better expressed in changes in Gf than in Gc.…”

“…It can be noted that Gf instead Gc could be less sensitive to environmental intervention, and, in principle, Gf may impact the resemblance between parents-offspring in intelligence. However, until now the only study linking heritability across cognitive abilities was the study of Kan, Wicherts, Dolan and van der Maas (2013). Contrary to traditional assumptions, this study identified that most heritable abilities are in fact the most culture-dependent abilities, i.e., Gc would be more heritable than Gf.…”

“…On the other hand, IQ differences between mothers-offspring in the same measure (SPM test) tended to be negative in low-SES families (offspring had higher performance than mothers) and positive in middlehigh-SES families (offspring had less performance than mothers). The authors of this study are inclined to consider the hypothesis of Kan et al (2013) and the studies of Harden et al (2007), Tucker-Drob and Bates (2016) and Turkheimer et al (2003) to explain the obtained results. The genotypeenvironment covariance through SES could influence the coefficients of cognitive heritability, where Gc would be more inheritable than Gf.…”

The Role and Sources of Individual Differences in Critical-Analytic Thinking: a Capsule Overview

“…Although there is a certain amount of fluctuation in these estimates for various indicators of fluid reasoning and crystallized knowledge, with the latter being more heritable than the former (Kan et al 2013), the field has converged, after a number of meta-analyses, on the estimate of 0.5 for general cognitive ability, which is a higherorder index derived from both fluid and crystallized capacities (Plomin et al 2013a). Although there is not unanimous enthusiasm regarding the value of heritability and familiality studies to the field (Charney 2012;Nisbett et al 2012;Richardson 2013), there is still a massive related research effort to further differentiate and stratify the obtained estimates throughout the life span (e.g., Haworth et al 2010;van Soelen et al 2011) and in the context of different moderators (e.g., Molenaar et al 2013).…”