The most incisive guide to issues facing the American family today . . . An invaluable resource for anyone wishing to stay on the cutting edge of research on family trends.
-W. Bradford Wilcox
Associate Professor of Sociology, University of Virginia
It has long been noted that marriage serves to “civilize” both men and women—to make them more productive, happier, healthier, and to suppress negative behaviors—especially those related to delinquency and violence. Now three scholars from the University of North Carolina at Chapel Hill seek to study further exactly how marriage manages to change previously criminal behaviors. What they find is that marriage actually interacts with a person’s genetic makeup to suppress violent and delinquent behavior.
The researchers begin by highlighting the need for their research. While previous studies into gene-environment interaction (G X E) have limited their focus to one or a few genes, their study examines “a large number of genetic variants.” They explain, “Drawing on data from the National Longitudinal Study of Adolescent to Adult Health . . . we examined whether marriage moderates the collective influence of 580 single nucleotide polymorphisms (SNPs) in 64 genes on delinquency and violence.” This broadened scope is necessary, the researchers claim, because “[a]ntisocial behavior . . . is influenced by a large number of genes.” Their study method “estimates a heritability parameter: the proportion of variance in the phenotype that is jointly explained by the SNPs. We examined the Gene X Marriage interaction by comparing the proportion of variance in antisocial behavior explained by 580 SNPs among married and unmarried individuals.”
For their measures, the researchers used “delinquency and violence,” including theft, selling drugs, breaking and entering, physical fighting, and use of weapons, among other indicators. A second measure was “desistence,” the process through which delinquent individuals gave up their delinquent or violent behaviors. The researchers controlled for a number of variables, including “age, gender, race, education, churchgoing frequency, household size, verbal IQ . . . score, parental education, closeness to parents, and bio-ancestry scores.” First, they examined the moderating effect of marriage in a generalized estimating equation. Next, they extended the model to estimate “the proportion of phenotypic variance that is accounted for by the linear, additive effects of the SNPs.”
The researchers discovered that marriage does indeed suppress genetic influences towards antisocial behavior: “Overall, the percentage of variance [in antisocial behavior] explained was significantly smaller in married individuals than in unmarried individuals, suggesting that marriage may suppress the collective influence of the genes.” Aware that selection, age, and population heterogeneity (defined as “individuals’ different propensity to engage in deviant behavior”) may all confound the effects of their findings, the researchers ran separate analyses. For all three, the marriage effect remained.
In closing, the researchers discuss the implications of their findings: “Past inquiries about the effect of marriage on antisocial behavior have primarily focused on the social, behavioral, and psychological aspects. . . . We found that marriage could work through a biological pathway—the modification of genetic effects—to deter delinquency and violence.” They highlight that though many other studies have made it seem as though environment has little effect on biology, theirs actually shows the opposite: “The effect of genes was conditional on the environment.”
So powerful is the effect of marriage, in other words, that it even alters the expression of biology. Policymakers should take such findings into account when discussing how best to curb violence and crime.
(Yi Li, Hexuan Liu, and Guang Guo, “Does Marriage Moderate Genetic Effects on Delinquency and Violence?” Journal of Marriage and Family 77 [October 2015]: 1,217-33. DOI: 10.1111/jomp.12208.)