So instead of asking why parents of daughters split up, it's worthwhile to ask, "Why do mothers of daughters leave their husbands more often than mothers of sons," Kelly said.
Another way of looking at the daughter-divorce effect, Kelly said, is to look at what about daughters might make a woman more likely to leave her husband.
Past statistics show that adult daughters living at home reduce the household workload (which falls largely on the mother's shoulders), while adult boys increase it, she said, so it's possible that women can anticipate support from their daughters more so than from their sons, making them "less willing to tolerate negative behavior in a spouse."
Heitler agrees, adding that women within a family -- mothers and daughters -- form a family within a family, offering social support to each other that a son might not offer a mother.
With this kind of emotional support and protection from being lonely (a huge concern expressed by many women considering divorce), "a husband who is being really difficult becomes dispensable," she said.
As far as Moretti and Dahl's observation that mothers of daughters are less likely to remarry and stay remarried following a divorce, a more mother-focused explanation would be that daughters make a new husband less necessary because they are offering social support, Heitler said.
Alternatively, a mother may be more wary of bringing a possible predator into her daughter's life by dating again, Kelly said.
According to Heitler, sticking with an unhappy marriage may seem less appealing if a woman feels she is teaching her daughter the wrong things about love and marriage, a concern she said divorced women have expressed in her practice.
"They think, it's hard to go through a divorce, but at the same time I don't want this to be a model of what marriage should be to my daughter," she said.
She said that often there is a multigenerational pattern of abusive husbands these women are trying to break.
So do girls drive parents apart or just encourage mothers to leave dysfunctional relationships? Do boys actually help marital relations by increasing the devotion and commitment of the father or make parents wary of splitting?
Unfortunately, the census data that allowed for Moretti and Dahl's work does not offer a definitive answer as to why couples with girls are more likely to break up, but in future research, these are questions that Kelly said she hopes to explore.