Individual differences in performance on tests of cognitive ability is one of the oldest and most studied areas of genetic research (Knopik, Neiderhiser, DeFries, & Plomin, 2017). The majority of this research focuses on general cognitive ability (g) (Plomin & Deary, 2015), which is the highest level in the Cattell-Horn-Carroll (CHC) hierarchical model of intelligence (McGrew, 2009). Family, twin and adoption studies converge on the conclusion that g is about 50% heritable (Chipuer, Rovine, & Plomin, 1990). A surprising finding is that the heritability of g increases dramatically across the lifespan – from about 20% in infancy to 40% in childhood to 60% in adulthood (Briley & Tucker-Drob, 2013; Haworth et al., 2010; Plomin, 1986).
Much less is known about the genetics of the middle level of the CHC model, which includes 16 broad factors such as reasoning, comprehension-knowledge, processing speed, reading and writing, and quantitative knowledge (Coyle & Greiff, 2021). These factors encompass hundreds of individual tests that comprise the lowest level of the CHC model. We refer to this middle level of the CHC model as specific cognitive abilities (SCA), even though we acknowledge that these factors are not completely independent of g. Despite the fact that SCA are correlated with g, it seems reasonable to review research that attempts to assess domains that are more specific than g, such as reading and writing, visual processing, and short-term memory.
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What your genes say about how you think