THAT the children of divorced parents are more likely, when they grow up, to get divorced themselves is well known. What is not known is how much this tendency is the result of nurture (with children manifesting, in later life, behaviours learned from their parents), and how much it is caused by nature (with children inheriting from divorced parents the sorts of genes that lead to marriage-breaking behaviour). That genes are important has, though, now been confirmed by a study published in Psychological Science by Jessica Salvatore and Kenneth Kendler of the Virginia Institute for Psychiatric and Behavioural Genetics.

To explore the role of genes Dr Salvatore and Dr Kendler turned to the Swedish national registries. These databases store, for all residents of Sweden, information on sex, year of birth, year of death, marital status, criminal activity, education and alcohol abuse. They also contain details of both the biological and the adoptive parents of adopted children.

Using these data, the researchers set about the daunting task of analysing the marriages of 19,715 adopted children, to see how often these ended in divorce and whether that divorce rate bore any relationship to divorces among their adoptive and biological parents. This analysis showed that such children were 20% more likely to divorce if their biological parents had divorced than if those parents had stayed together, but no more (and no less) likely to do so if their adoptive parents had split up.

With this result under their belt, Dr Salvatore and Dr Kendler then looked at adopted and biological siblings brought up in the same households. As expected, they found that individuals showed a similar tendency to divorce to that of their biological siblings but not to that of their adopted siblings. They also discovered that if one biological sibling divorces, the others are 20% more likely to do so than would otherwise be the case. This is not true for adoptive siblings.

All of these results strongly suggest, Dr Salvatore and Dr Kendler argue, that genetic factors play an important part in the “transmission” of divorce across generations—and that this needs to be taken into consideration when offering psychological support and relationship counselling to people whose parents have split up, even if those people never knew the parents in question.