Marriage and genetic variation across the lifespan: not a steady relationship?

The prevalence of marriage varies across the lifespan, as does its importance to reproduction and the nurturance of children. We examined genetic and environmental influences on self-reported marriage at each decade from 20 through 70 years of age, using data collected for the Duke Dementia Study, a followed-up subset of the World War II Veteran Twin Registry. Genetic influences best fit a common factor model, supplemented by another, age-specific, genetic factor at age 30. Broad heritability increased from age 20 through 40, and then decreased to zero by ages 60 and 70. A longitudinal Cholesky model best described environmental influences on marriage across the lifespan. Shared environmental factors showed their greatest influence at age 20, no influence at 30 or 40 years, and then, reappeared with influence at 60 and 70. Variance due to error and unique environmental influences increased steadily to age 50 years and then declined slightly.