A study recently published in the journal Evolutionary Psychology Science examined cooperative and conflictual aspects of affinity relationships (ie relationships with in-laws). The results showed that both men and women report more conflicts with their mothers-in-law than mothers, and that mothers report more conflicts with their daughters-in-law than daughters.
Building lasting relationships with the relatives of long-term partners facilitates bonding and investment in the offspring of both sexes. Despite the numerous benefits of affinity relationships, conflict is also a central feature. Hamilton’s rule helps explain why biological relatives invest in each other’s survival, which is also seen in animals. For example, older female squirrels sometimes signal the presence of predators, revealing their location, and sacrificing their own lives to warn their biological relatives. Although mothers and fathers are not related in most societies, they cooperate and share a common interest in the survival of their children, creating interdependence between two families. Because affines (ie, relatives by marriage) have shared genes with only one parent, their interests typically coincide with that parent.
Jessica D. Ayers and colleagues write, “This causes affins to experience similar types of conflict as unrelated parents, and may motivate behaviors that favor the interests of their genetic relatives, even at the expense of their related relatives. The affinity conflict can therefore be viewed as an extension of the genetic conflict between mothers and fathers.”
Given the shorter interval between births that human females have compared to non-human apes, females face the challenge of caring for multiple offspring simultaneously and benefit from positive affinity relationships. Ancestor women may have relied on the help of biological relatives for childcare; However, this would not be possible if the genetic relatives were not geographically close. This would have required the support of affinity relationships in childcare. And because affines have a genetic interest in offspring, this would encourage them to provide the same quality of childcare as the mother’s genetic relatives would.
While female affinity cooperation focuses on caring for kin and maintaining social bonds, male affinity cooperation is concerned with gaining and maintaining social relationships, finding a partner, protecting oneself and others, and investing resources in children.
Moms and daughters-in-law tend to have different fitness interests, which can create conflict. “For example, the resources of a mother-in-law’s partner/mother-in-law’s partner are limited, so the daughters-in-law prefer their husband to allocate resources to her and their family, while the mother-in-law prefers her son’s allocation of resources to his other family members.”
Conflict tends to occur in the same areas as cooperation, including childcare, material resources for relatives, and spending time with children. Conflicts in these areas could lead to the acquisition of other social relationships, which can later become a source of conflict. For example, “Child care conflicts can affect the quality of mother-daughter-in-law relationships, resulting in the daughter-in-law seeking additional social connections to help with childcare — which can worsen her relationship with her mother-in-law.”
Partner search and attachment as well as self-protection can also be sources of conflict in affinity relationships, since these interfere with the fitness interests of mother and daughter-in-law.
In this study, Ayers and colleagues examined collaboration and conflict between in-laws. A total of 308 participants were recruited via online platforms. Participants answered demographic questions (e.g., age, gender, education, marital status) and provided the names/initials of their kindred and genetic relatives that would emerge later in the study. Participants answered a variety of questions about these relationships, such as: B. the duration and general cooperation and extent of conflicts in different areas (e.g. resources, social relations, security). The researchers derived a metric for the ratio of conflict to interaction to assess whether these relationships were primarily characterized by conflict or cooperation.
The results suggest differences in perceptions of conflict involving genetic and kindred kin. Both men and women reported more conflicts with their mothers-in-law than mothers, and mothers reported more conflicts with daughters-in-law than daughters.
In addition, fathers reported more conflicts with daughters than with daughters-in-law. It could be that these conflicts revolve around mate choice and the addition of a new affinity relationship in a father’s coalition network. If a father believes that his ancestral son would strengthen the coalition, one would expect that conflict to diminish over time.
Areas where participants reported the most conflict included material resources and caring for loved ones, both of which are critical to long-term reproductive success.
A limitation of the current work is that participants had to have relationships with living genetic and affine mothers to be included in the analyses. This would have excluded participants involved in conflicting relationships that were ending, introducing a bias in the results in favor of collaboration.
The study “Mother-in-Law Daughter-in-Law Conflict: an Evolutionary Perspective and Report of Empirical Data from the USA” was authored by Jessica D. Ayers, Jaimie Arona Krems, Nicole Hess and Athena Aktipis.