Period of Marriage and Genetic Similarity in Height between Spouses in the United States over the 20th Century.

Social norms regarding who marries whom have changed dramatically in the United States across the 20th century. These changes may influence the level of genetic similarity between spouses. This study investigates whether genetic similarity in height between husband and wife was influenced by a historical transition in spouse selection criteria. The great transition from the companionate marriage to the individualized marriage occurred in the 1960s. In the companionate marriage, husband and wife chose each other as companions, and the emphasis was on playing marital roles well: husbands being good breadwinners and wives being good homemakers. In the individualized marriage, the emphasis switched to individual feelings, and as a result, when choosing their partners people tended to pay less attention to height, suggesting a smaller genetic correlation for height between spouses. Using data from the Health and Retirement Study, we found that the genetic correlation for height declined substantially in the individualized marriage. We conducted a number of analyses to test for the confounding effects of cohort and age and to address population stratification, selection issues, and genetic relatedness between spouses. Evidence suggests that the effect of this transition is robust.