IQ is Highly Heritable

Source: Association for Psychological Science, 2016

 the heritability of intelligence has been shown consistently to increase linearly throughout the life course in more than three decades of research in longitudinal as well as crosssectional analyses and in adoption as well as twin studies (McGue, Bouchard, Iacono, & Lykken, 1993; Plomin, 1986; Plomin & Deary, 2015). For example, as summarized in Figure 3, an analysis of cross-sectional data for 11,000 pairs of twins—larger than all previous twin studies combined—showed that the heritability of intelligence increases significantly from 41% in childhood (age 9) to 55% in adolescence (age 12) and to 66% in young adulthood (age 17; Haworth et al., 2010). 

Some evidence suggests that heritability might increase to as much as 80% in later adulthood independent of dementia (Panizzon et al., 2014); other results suggest a decline to about 60% after age 80 (Lee, Henry, Trollor, & Sachdev, 2010), but another study suggests no change in later life (McGue & Christensen, 2013).

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