Is divorce hereditary?

Can genes help explain why people separate? 

Sociologist Ruth Eva Jørgensen believes they can. In her doctoral research project, she explored the connection between genetics and relationship breakdown, and the extent to which the likelihood of separation is something that ‘runs in the family’:

“Genes and genetically informed methods can help us understand processes of transmission between generations, from parents to children,” says Jørgensen, who recently defended her doctoral dissertation at the University of Oslo.

Common explanations

There are many different reasons why relationships end in separation. In sociology and demography, researchers have focused on differences between groups and factors such as age, socioeconomic background, and education.

International and Norwegian research has shown that:

• People with higher levels of education are less likely to get divorced.

• Women are more likely to initiate a separation.

Other studies have examined the consequences of divorce for women and men.

“A German study, for example, found that men experience more severe short-term effects on their quality of life, while women are more likely to face lasting negative financial consequences.”

Explains 9 per cent among women

Genetics has long been something of a ‘black box’ in research on relationship breakdown. Although twin studies have established that genetic factors influence the likelihood of separation, we still do not know what this genetic influence consists of or which traits are important.

Jørgensen has used data from Norwegian registries and the Norwegian Mother, Father and Child Cohort Study (MoBa) to better understand the role of genetics.

“The registry data provides information about relationship breakdowns, among other things, while MoBa contains genetic data,” she explains.

In the first analysis, the researchers attempted to estimate the overall influence of genetics.

They found a small gender difference.

“Overall, genetics appears to explain slightly more of the variation in relationship breakdown among women (9 per cent) than among men (3 per cent),” she says.

Jørgensen explains:

“For women, genes collectively explain 9 per cent of the variation in the risk of relationship breakdown. This means that there are many other factors that explain why couples separate.”

Four predispositions were associated with a lower probability

In addition to estimating the heritability of an outcome, there is another tool frequently used by researchers: polygenic scores. Using MoBa data, the researchers calculated several such scores for a range of traits.

A polygenic score is a measure of how many of the numerous small genetic variants that previous research (GWAS studies) has linked to a particular trait a person possesses. The more of these variants a person has, the higher their score.

Among other things, they found that higher polygenic scores (PGS) for education, subjective well-being, neuroticism, and older age at first sexual intercourse were all associated with a lower likelihood of experiencing a relationship breakdown.

This means, for example, that people with a genetic predisposition towards higher education had, on average, experienced fewer relationship breakdowns. Whether people actually had a higher education was therefore not taken into account.

The finding concerning neuroticism was perhaps particularly surprising.

“If we were to speculate about what this means, it could be that people with higher levels of neuroticism also have a greater need for the security that a partner can provide. But that is a possible explanation of the mechanism, not something we can actually demonstrate.”

Jørgensen adds that the researchers found no significant differences between women and men in these associations.

Genes operate through the environment

Jørgensen emphasises that the findings apply to people living under specific social conditions in Norway today. The significance of different predispositions can vary between societies and historical periods.

“You write that genes ‘operate through the environment’ – what do you mean by that?”

“Our genes cannot operate on their own. They depend on other actors and on opportunities in the surrounding environment. If we go back a hundred years, there were far fewer relationship breakups. Not because we humans were genetically different, but because social structures and legislation were different. In a society where ending a relationship is illegal and nobody separates, there is no variation in breakups for genetics to help explain,” the researcher says.

We can also imagine that different genetic predispositions may have more or less room to manifest themselves depending on the social context in which a person lives.

"So the findings do not show that relationship breakdowns are ‘in our genes’?"

"No, that would be a deterministic interpretation," says Jørgensen.

Sociology + genetics = true

Jørgensen believes that genetically informed methods can offer insights that previous sociological research has overlooked.

“When studying what is passed down ‘socially’ from one generation to the next, much of the earlier research has focused primarily on the family environment,” she says.

But children inherit 50 per cent of their genes from each biological parent. This means that factors beyond family circumstances and upbringing may help explain why parents and children are similar or experience similar outcomes.

“This makes it harder to determine how much of children's outcomes can actually be attributed to their family environment and, in our case, to their parents' separation. It also makes it difficult to distinguish these influences from characteristics that parents and children share through biological inheritance,” she says.

Sociologists are generally most concerned with environmental factors, Jørgensen adds.

“But if we want to understand the relationship we're studying, it helps to account for other factors that might influence it. Genetics is an obvious factor to consider,” the researcher says.

Some heritability

To better distinguish between these explanations, Jørgensen and her colleagues have used two different approaches: an adoption study and a children-of-twins study.

“In the adoption study, we have adopted children who do not share genes with their adoptive parents. We then match the adoptive families as closely as possible with other families in the registry data, so that the families are as comparable as possible,” she says.

In the children-of-twins design, researchers analyse the children of twins. Children of identical twins share 25 per cent of their genetic material, while children of fraternal twins share an average of 12.5 per cent. Among other things, the researchers examine differences within families where one twin has experienced a relationship breakdown and the other has not. These within-family comparisons help control for shared genetic factors and childhood environments.

In families with biological children, they find a strong association between parents' and children's relationship breakdowns. In adoptive families, however, this association disappears. The children-of-twins study shows a similar pattern.

“This suggests that genetics is part of the explanation for why relationship breakdowns are passed down through generations. Much of the association may be explained by the fact that parents and children resemble one another in several ways, including genetically,” says Jørgensen.

Many find a genetically similar partner

“Genetic methods are both common and useful, including in research on social outcomes,” Hans Frederik Sunde, a researcher at the Norwegian Institute of Public Health (NIPH), writes in an email to Kilden magazine.

Sunde has studied the effects of what researchers refer to as partner similarity.

“In other words, whether similar people are attracted to one another, whether partners become more alike over time, and what consequences these similarities may have.”

He has also used genetic methods in his research. Together with colleagues, he has shown that partners share genetic predispositions for traits such as education, height, BMI and, to a lesser extent, personality.

“This suggests that some of the similarity is due to similar people finding each other, rather than simply becoming more alike over time,” Sunde explains.

Also found small gender differences

"And what does your research say about the significance of gender?"

“My primary focus is not on gender, but we examine differences between women and men when relevant. For example, in our divorce study, we find, as Jørgensen and her colleagues do, that women's predisposition to divorce appears to have a slightly greater influence on whether a couple divorces than men's predisposition. But the difference is not very large,” says Sunde.

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Translated by Alette Bjordal Gjellesvik

This article was first published in Kilden genderresearch.no. Read the original here.

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