Mirkka Danielsbacka, Antti Tanskanen & Anna Rotkirch
Conflicts with in-laws are a common feature of human family life, yet this phenomenon has been little studied in industrialised societies. Here we use survey data of contemporary Finns (n=1,202) to investigate how parenthood is associated with the likelihood of conflicts with parents and parents-in-law. Based on inclusive fitness and inverse relatedness theory, we hypothesized that (i) spouses would be less likely to report conflicts with their own parents than with their parents-in-law and (ii) conflict-proneness with own and affinal parents would be more similar among who had children compared to childless couples. Support was found for the second but not the first hypothesis. Overall, spouses reported more conflicts with their own parents than with their in-laws. Compared to childless spouses, spouses with children had a higher likelihood of conflicts with their parents-in-law, but a similar likelihood of conflicts with their own parents. Contact frequencies were related to conflict occurrence, but results were also robust after taking contact frequencies into account. Paternal grandmothers who provided more grandchild care had more conflicts with their daughters-in-law. We conclude that the inverse relatedness arising between lineages through a grandchild renders affinal relations more akin to consanguineal relations in contemporary Finland.
Final version published in Evolutionary Psychological Science.