One of my colleagues has a coffee mug that I think summarizes the whole genes vs. environment debate pretty well: “Nature or nurture, either way it’s your parents’ fault.” Cheeky coffee mugs aside, one of the enduring legacies that our parents give us is their DNA. We know that genes influence all sorts of outcomes—how tall we are, how much we weigh, the color of our eyes, and our likelihood of developing certain diseases and disorders. But, it was only about 25 years ago that researchers started to look at the influence of this genetic blueprint on our relationship outcomes.
In a landmark study in this area from the early 1990s, researchers estimated the heritability of divorce to be about 50%.1 What does a heritability estimate like this mean? Imagine a city or town where all of the people are either married or divorced. A heritability estimate of 50% means that the genetic differences between people in that city can explain half of why some people in that city stay married and why others get divorced. (What explains the other half of why some people get divorced? The environment!) Importantly, what a heritability estimate doesn’t mean is that half of the reason that Joe or Mary, individuals who live in our imaginary city, get divorced. In other words, a heritability estimate tells us that genetic factors play a role in general, but it does not explain why any one of us will experience divorce.
A heritability estimate also doesn’t tell us—by itself—whether we carry the specific genes or genetic variants that make us more likely to experience divorce. To find those genes, we would have to take a different approach. Right now, the most popular approach for gene identification is the genome-wide association study, which looks across the genome to see whether there are genotypic differences between people who do and do not have a trait or behavior of interest. For example, this analysis could determine if there are specific genetic variants associated with whether someone has straight or curly hair2. No one has conducted a genome-wide association study of divorce (yet!), so it will be a while before we can ship off a saliva sample to 23andme (or any other direct-to-consumer genetic testing company) to find our risk of divorce.
A complicating factor in any such search for “divorce genes” is that divorce is what we call a “complex” outcome. In genetics, when we say that a trait or behavior is complex, we mean that there are multiple genes and genetic variants that influence that trait or behavior. Most of the things that psychologists and relationship researchers study—like how neurotic someone is, whether they have an alcohol or drug problem, or whether they are likely to get divorced—are complex traits. Contrast this with other types of outcomes that a single gene causes, such as Huntington’s disease or cystic fibrosis. The effect of each individual gene on a complex outcome like divorce is expected to be exceedingly small. This makes the search for “divorce genes” very challenging, like trying to find needles in a haystack.
What can we do in the meantime if we are interested in informally assessing our “genetic load” (or predisposition) for divorce? As with anything that is genetically influenced, simply look up at your family tree. There are even free online tools for pedigree mapping (like Progeny) if you want to visually summarize your risk. Family history captures both genetic and environmental risk that runs in families (since for many of us the same people who provide us our genes also provide us our home environments). For this reason, it’s not a perfect tool for isolating genetic risk only. But since we know that genetic factors contribute to divorce, family history gives us at least a rough guess about our genetic load. And if we know that we are at genetic risk for divorce (based on our family history), what can we do about it? That question remains an open one in the field; however, it is worth noting that a genetic predisposition does not predetermine our destiny (having the genetic predisposition for divorce does not mean that you’ll definitely get a divorce). But, knowing that there are genetic factors on divorce may point us toward better targets for marital interventions with distressed couples—a topic to be explored in a later post!
1McGue, M., & Lykken, D. T. (1992). Genetic influence on risk of divorce. Psychological Science, 3, 368-373. doi:10.1111/j.1467-9280.1992.tb00049.x
2Medland, S. E., Nyholt, D. R., Painter, J. N., McEvoy, B. P., McRae, A. F., Zhu, G., . . . Martin, N. G. (2009). Common Variants in the Trichohyalin Gene Are Associated with Straight Hair in Europeans. American Journal of Human Genetics, 85, 750-755. doi:10.1016/j.ajhg.2009.10.009
Jessica E. Salvatore, Ph.D. – Website
Dr. Salvatore is an Assistant Professor in the Department of Psychology at Virginia Commonwealth University. Her research focuses on substance use and romantic relationships, and the use of genetically informed designs to understand the links between substance use and relationships.