Thursday, November 9, 2017

A Gene for Divorce?

From Science of Relationships:
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. (Read more.)

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