Marriage or cohabitation? Genetic influences on couples’ choice of union type

The choice between marriage or cohabitation is shown to be associated with many demographic and socioeconomic factors, as well as personal relationship assessments and mental health. However, the role of individual differences linked to genetic factors has attracted less attention. This study uses genetically informed data from the Norwegian Mother, Father, and Child Cohort Study (MoBa) to investigate whether polygenic scores related to educational attainment, fertility, personality traits, and mental health are associated with union type at first birth, as well as the subsequent transition to marriage. Our results indicate that genetic factors influence parental union type choices through educational attainment, reproductive outcomes, and positive and negative emotionality. For union type at first birth, polygenic scores for educational attainment and postponement of reproductive activity have the strongest associations. For the subsequent transition to marriage, associations with polygenic scores for subjective wellbeing and educational attainment are most salient. However, there is also some indication that polygenic scores for negative emotionality are negatively associated with marriage among men. These findings give insights into potential selection processes and the chain of intermediate phenotypes through which genetic factors influence couples’ choice of union type.