Phenotype–environment correlations in longitudinal twin models

Abstract

Gene–environment correlation (rGE) exists both within and between families. Between families, accumulating rGE has been used to explain dramatic changes in phenotypic means over time. The Dickens and Flynn model of increases in cognitive ability over generational time, for example, suggests that small changes in phenotype can lead to subsequent reallocation of environmental resources. This process sets up a reciprocal feedback loop between phenotype and environment, producing accumulating rGE that can cause large changes in the mean of ability, even though ability remains highly heritable in cross-sectional data. We report simulations suggesting that similar processes may operate within twin and sibling pairs. Especially in dizygotic twins and siblings, small differences in phenotype can become associated with reallocations of environmental resources within families. We show that phenotype–environment effects can account for age-related increases in rGE, rapid differentiation of siblings raised together, and widely reported increases in the heritability of behavior during childhood and adolescence.

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“…This finding is somewhat unexpected given that adult phenotypes tend to demonstrate relatively small contributions from the shared environment (Beam & Turkheimer, 2013).…”

“…The DZ twin who is less attentive or more hyperactive may, because of their phenotypic characteristics, either seek out or be placed into environments that contribute to greater expression of these traits (or vice versa for the more attentive, less hyperactive twin). Beam & Turkheimer (2013) note that rPE can lead to false positive G×E results.…”

“…What results from such an interactive process is fewer individuals at the high end of the SES spectrum experiencing more serious symptomatology, which is broadly consistent with our data observations. Such E×E interaction may also arise from phenotype-environment correlation (rPE; Beam & Turkheimer, 2013). Pathological processes are individual processes that take off on top of genes, and an individual's twin is not correlated with such processes.…”

“…Phenotype-environment correlation is a transactional process by which small phenotypic differences result in differential exposure to environments (by either evocative or active means), which could then reciprocally affect phenotypic expression in a chain of interactions that eventually leads to large changes in phenotype (Beam & Turkheimer, 2013;Dickens & Flynn, 2001), and, consequently, large within-pair differences. That is to say, this type of process will induce expansions in within-family variance in a phenotype under certain conditions; our results suggest that deprived environments may be one such condition.…”

“…It is absolutely true, however, that some individuals are more prone toward obesity, internalizing disorders, or substance use than other individuals, and that these phenotypes are influenced by genetic factors. At the same time, it is often the phenotype, and not the genotype, that is responsible for individuals selecting into protective or iatrogenic environments that reciprocally affect the phenotype, thereby furthering pathological (or protective) processes (Beam & Turkheimer, 2013;Beam, Turkheimer, Dickens, & Davis, 2015;Bronfenbrenner & Cici, 1994;Dickens & Flynn, 2001;Turkheimer, 2004;Turkheimer & Gottesman, 1996). Longitudinal research fitting models that account for phenotype-environment correlation (rPE) may be influential in demonstrating how pathology (exhibited primarily by those in the skewed distribution of a dually-distributed trait) develops and/or is maintained.…”