Having kids might help you understand what your own parents went through in raising you and what your partner's parents went through in raising them. Still, it might not help you get along any better. A new study in the journal Evolutionary Psychological Science reports that at least among Finns, having kids is associating with fighting more with your family, both your own and your in-laws.

In general, people tend to fight with their families. In a survey of 1200 people in Finland, both childless couples and ones with kids reported plenty of fighting with their own parents. But couples with kids were more likely to report fighting with their in-laws, too.

Other research has shown that people tend to be more altruistic when family ties are involved, a phenomenon called the “kinship premium.” But this study shows that it can go both ways. These researchers call it the “kinship penalty.” Yes, blood is thicker than water, but that doesn't mean people aren't prone to fighting with their family, as anyone who's been to a family holiday party can attest.

When a couple has kids, they create greater ties to their parents-in-law, who have suddenly become grandparents. This makes some intuitive sense—if you don't have kids, and you split up with your wife, your parents might never have a reason to see your wife again, but if you and your wife get a divorce after having kids, your parents might still interact with the mother of their grandchildren. But becoming closer to your partner's parents also can lead to tension and conflict.

The trope of the clash between women and their mothers-in-law isn't entirely a myth, the study finds, especially when Grandma is taking care of the kids. Daughters-in-law were more likely to report conflict with their mothers-in-law when the grandmother was providing childcare.

The study only tackled the topic of Finnish families, so it's possible that the results might look a bit different in another culture, especially since Finland has a notoriously generous government support system that makes being a parent there a vastly different experience than it is for people who live in countries without those policies. The effect might be even worse if you live in a place like Italy, where grandmothers remain one of the main sources of childcare compared to a place like Finland, where it's very rare for grandparents to be the dominant childcare providers.