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. 2015 Jan;45(1):71-83.
doi: 10.1007/s10519-014-9693-3. Epub 2014 Dec 10.

Genotype × cohort interaction on completed fertility and age at first birth

Daniel A Briley  1 , K Paige Harden, Elliot M Tucker-Drob
Affiliations

Genotype × cohort interaction on completed fertility and age at first birth

Daniel A Briley et al. Behav Genet. 2015 Jan.

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 1920-1935 birth cohort, but rose substantially for the 1936-1955 birth cohort. For the 1956-1970 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.

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Conflict of interest statement

Conflict of Interest

Daniel A. Briley, K. Paige Harden, & Elliot M. Tucker-Drob declare that they have no conflict of interest.

Figures

Figure 1
Figure 1
Hypothetical decline in completed fertility from birth cohorts of 1920 to 1970 where fertility falls along a logistic curve. A. Expected completed fertility for the population average, late fertility adopters, and early fertility adopters. B. Area between the late and early adopter curve, which could potentially be related to genotypic differences between individuals.
Figure 2
Figure 2
Cohort trends in full MIDUS sample. A. Mean and variance of completed fertility, sex adjusted. B. Mean and variance of age at first birth, sex adjusted. C. Mean and variance of completed fertility, males. D. Mean and variance of age at first birth, males. E. Mean and variance of completed fertility, females. F. Mean and variance of age at first birth, females.
Figure 3
Figure 3
Quantitative genetic decomposition of fertility outcomes in the twin subsample of MIDUS. Unstandardized genetic and environmental influences are presented for A. completed fertility using LOSEM, B. age at first birth using LOSEM, C. completed fertility as a spline function of birth year, D. age at first birth as a spline function of birth year, E. completed fertility as a quartic function of birth year, and F. age at first birth as a quartic function of birth year. Squared ACE pathway expectations are presented.
Figure 4
Figure 4
Expected sex adjusted phenotypic cohort trends based on twin subsample results assuming a population average with subgroups possessing genetic dispositions for early and late adoption of novel fertility behaviors. A. Phenotypic trends in completed fertility for the population average, a subgroup with genetic dispositions for late adoption (i.e., +1 SD genetic effect), and a subgroup with genetic dispositions for early adoption (i.e., −1 SD genetic effect). B. Phenotypic trends in age at first birth for the population average, a subgroup with genetic dispositions for late adoption (i.e., −1 SD genetic effect), and a subgroup with genetic dispositions for early adoption (i.e., +1 SD genetic effect).
See this image and copyright information in PMC

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