Genetics of Experience: Genetically Sensitive Approaches to Measuring Childhood Environment
Environmental experience is not free of genetic influence. Through genetically-influenced behaviours, genes can influence exposure to certain environments: gene-environment correlation. Particular genotypes may also be more or less sensitive to the effects of the environment: gene-environment interaction. Embedding measured environmental experiences and the childhood outcomes they correlate with into genetically sensitive designs is a powerful approach to unravelling the mechanisms at the interface between nature and nurture. This thesis explored children’s environmental experience using data spanning 14 years of the population-based Twins Early Development Study (TEDS). Bivariate twin model fitting showed a significant genetic component linking children’s heritable experience of the chaotic home and their academic achievement. Genes confound a previously assumed environmental effect. The continuous moderation model revealed greater variation in the IQ of children from low socioeconomic status (SES) families. This greater variation was the result of SES moderation of the environmental, not genetic, effect on IQ. Longitudinal twin model fitting showed a bi-directional cross-lagged effect between disruptive behaviour and children’s experience of the chaotic home. The effect of household chaos on disruptive behaviour was environmentally mediated, and in the reverse process, disruptive behaviour did not account for the heritable component of home chaos. Multivariate twin modelling revealed a substantial common genetic liability between behaviour (internalizing, externalizing, and cognitive ability) and the psychosocial experience of peer victimization. Statistical genetic techniques using whole-genome data confirmed that victimization is a typical complex trait with a common genetic liability. The approach taken here was to explore gene-environment mechanisms at the interface between nature and nurture using a variety of childhood experiences rather than focusing on one particular environment. The examples of home chaos, SES, and peer victimization highlight the ubiquity of gene-environment interplay in a range of childhood experiences. Child-driven effects on the environment result in a genetic component to experience.
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