Genotype × Cohort Interaction on Completed Fertility and Age at First Birth

Abstract

Microevolutionary projections use empirical estimates of genetic covariation between physical or psychological phenotypes and reproductive success to forecast changes in the population distributions of those phenotypes over time. The validity of these projections depends on relatively consistent heritabilities of fertility-relevant outcomes and consistent genetic covariation between fertility and other physical or psychological phenotypes across generations. However, well-documented, rapidly changing mean trends in the level and timing of fertility may have been accompanied by differences in the genetic mechanisms of fertility. Using a sample of 933 adult twin pairs from the Midlife Development in the United States study, we demonstrate that genetic influences on completed fertility and age at first birth were trivial for the 1920 to 1935 birth cohort, but rose substantially for the 1936 to 1955 birth cohort. For the 1956 to 1970 birth cohort, genetic influences on completed fertility, but not age at first birth, persisted. Because the heritability of fertility is subject to change dynamically with the social context, it is difficult to project selection pressures or the rate at which selection will occur.

Mega-analysis of 31,396 individuals from 6 countries uncovers strong gene-environment interaction for human fertility

“…Nevertheless, we find significant additive genetic influences on fitness traits such as NEB and AFB – substantial yet lower than heritabilities observed for morphological traits such as height [14,15,23,43]. Finding significant genetic influences on this these proxies of fitness suggests that, along with sociocultural changes surrounding fertility, genetic variants under selection have also changed [for review see 1,for review see 2,5,7,17,34,for comment see 44–46]. Gene-environment interaction can explain why we find additive genetic variance in fitness related traits despite natural selection.…”

“…Previous twin and family studies furthermore suggest that the level of heritability of fertility traits can change across time and space [5,7,34,35]. However, these differences could not be statistically validated.…”

“…Genetic effects on fertility outcomes are rather strongly dependent on an individual’s environment. Recently, social scientists have made large efforts to integrate molecular genetics into their research [1,2,23,34,38–42]. However, when it comes to reproductive health, environmental factors are also likely to be critical in understanding how genetic factors are modified in relation to fecundity and infertility.…”

Nonparametric Estimates of Gene × Environment Interaction Using Local Structural Equation Modeling

“…We have previously used LOSEM in a study of how birth cohorts differ in genetic influences on fertility behavior (Briley et al, 2015) and in a study of how the relation between pubertal timing and depression varies as a function of SES (Mendle et al, 2015). In both of these cases, we expected nonlinear G×E trends, but it was unclear what the exact functional form was.…”

Genetic Associations Between Personality Traits and Lifetime Reproductive Success in Humans

“…For example, societal changes in the 20 th century seem to have increased the role of individual differences in reproductive behavior, making features such as age at first attempt to get pregnant and number of children, heritable (Briley et al 2015;Kohler et al 1999). Other related behaviors, such as fertility motivation or the desired number of children have also proven to be genetically influenced in contemporary humans (Miller et al 2006).…”