Nature versus nurture: when divorce runs in the family, which one is it? Is divorce passed down through generations because children spend time around their separated parents, or because parents pass on their "divorce genes?"
But why is that? Is divorce transmitted across generations due to psychological and social factors - such as children tending to imitate their parents - or could there be a genetic influence at play?
A new study, which is soon to be published in the journal Psychological Science, gives more weight to the latter.
The research was carried out by scientists at the Virginia Commonwealth University (VCU) in Richmond, in collaboration with a team at Lund University in Sweden.
The first author of the study is Jessica Salvatore, Ph.D., an assistant professor in the Department of Psychology in the College of Humanities and Sciences at VCU.
Why does divorce run in the family?
Prof. Salvatore and her colleagues used so-called classical and extended adoption designs to study data available from Swedish national registries.
Speaking to Medical News Today about the methodology they used, Prof. Salvatore explained, "The basic idea with an adoption design is that it gives you a lot of traction on the question of whether something (like divorce) runs in families due to genetic and environmental factors."
"We looked at whether adoptees whose biological parents divorced were more likely to have their own marriages dissolve," she added. "We also looked at whether adoptees whose adoptive parents divorced were more likely to have their own marriages dissolve."
"If adoptees resemble their biological parents, we know that it's genetic factors that contribute to this resemblance because biological parents only give genes to their offspring," she explained.
Conversely, "If adoptees resemble their adoptive parents, we know that it's something about being raised in a divorced household that contributes to this resemblance because adoptive parents provide only an environment (not genes) to their adopted children."
In the classical adoption analyses, 19,715 adoptees - 52 percent of whom were male - had a similar divorce history as their biological parents but not their adoptive parents.
The scientists performed extended adoption analyses on 82,698 children, which revealed a significant environmental influence.
However, when the researchers tried to replicate these results "using within-generation data from adoptive and biological siblings," the results showed that "[a]doptees resembled their biological, but not adoptive, siblings in their history of divorce."
"Thus," the study authors conclude, "there was consistent evidence that genetic factors contributed to the intergenerational transmission divorce, but weaker evidence for a rearing environmental effect of divorce."
'A different picture' of divorce
Prof. Salvatore also spoke to MNT about the significance of the study, as well as its strengths and limitations. "We were surprised by the findings," she says.
"Previous studies on why divorce runs in families [...] have really focused on the pernicious effects that growing up in a divorced household has on one's own marital stability later in life. [But] in our study a different picture emerged."
Prof. Jessica Salvatore
This picture, she added, suggests that "[the] reason that the offspring of divorced parents are more likely to get divorced has to do with the genes that parents and children share, rather than the experience of seeing [their] parents split up."
"A strength of this study," Prof. Salvatore told us, "is that in an adoption design, the influences of genetics and the rearing environment are disentangled from one another."
She also admits some limitations to her research, saying, "[If] biological parents and adoptees have extensive contact before the adoption, this can cause an upward bias in their resemblance."
However, as Prof. Salvatore noted, "We conducted a series of sensitivity analyses that suggested that this wasn't the case."