Cognition is about 50% - 70% heritable at the population level. Heritability is maximized when people choose their own environments and experiences.
Gene-environment correlation states that people with more similar genes experience more similar environments and vice versa. Transactional models state that early-life behaviours, driven by genetics, lead to a person selecting particular types of environments. These environments have a causal effect on cognition, leading to the notion that the original behaviours led to these experiences and this cognition (e.g. having higher IQ leads to environments where you can stimulate IQ, which leads to an even higher IQ). Traits such as intelligence, motivation and intellectual interest are important in selecting these environments. Genes are thus very important in selecting environments which, in turn, have large impact on cognition. This leads to a large estimate of heritability.
The availability of environmental experiences is essential in choosing one’s own environment. Differences in heritability between groups could thus demonstrate important underlying developmental processes. Heritability differs along age/development and socioeconomic advantage.
Heritability increases with age as people tend to select their own environments more and more. Children select experiences in line with their genetic predispositions and these experiences stimulate cognitive development. This means that the early genetic influences on cognition will become amplified. Another explanation for the increased heritability with age is that new genes become activated later in development (e.g. biological changes of puberty).
There may be lower heritability in children with lower SES. This may be because people with lower SES have less freedom to choose the most enriching experiences which, in turn, lead to more heritability. SES disadvantage may not disrupt gene-environmental transactions in countries that ensure high quality healthcare and education (e.g. Scandinavian countries).
