Mother-In-Law Daughter-In-Law Conflict: an Evolutionary Perspective, Ethnographic Review, And
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Running head: AFFINAL CONFLICT 1 Mother-in-law daughter-in-law conflict: An evolutionary perspective, ethnographic review, and report of empirical data from the United States Jessica D. Ayers1, Jaimie Arona Krems2, Nicole Hess3, & Athena Aktipis1,4 1 Department of Psychology, Arizona State University 2 Oklahoma Center for Evolutionary Analysis (OCEAN), Department of Psychology, Oklahoma State University 3 Department of Anthropology, Washington State University 4Center for Evolution and Medicine, Arizona State University Corresponding author: Jessica D. Ayers, [email protected], Department of Psychology, Arizona State University, Tempe, AZ 85287-1104, United States. Acknowledgments: We would like to thank Lee Cronk for his helpful comments on this manuscript. AFFINAL CONFLICT 2 Abstract Relationships with genetic relatives have been extensively studied in the evolutionary social sciences, but affinal relationships have received much less attention, and little work has examined both cooperation and conflict among affines from an evolutionary perspective. Yet humans have extensive interactions with the kin of their mates, i.e., in-laws or affines, as humans form long-term pair bonds with mates, with both sexes investing heavily in resulting offspring, thus leading to many opportunities for interacting with extended kinship networks. To contribute to the scholarship on affinal bonds, and particularly on perceptions of affinal conflict, we conducted an ethnographic review and collected empirical data on cooperation and conflict among affines. Here we present (1) a sample 37 of ethnographies showing cross-cultural evidence of conflict in affinal relationships. We also report (2) empirical evidence of self-reported cooperative and conflictual aspects in affinal relationships in a Western sample. U.S. men and women both reported more conflict with mothers-in-law than with mothers, and mothers reported more conflict with their daughters-in-law than with their daughters. We also found that there was high conflict between mother- and daughter-in-laws in domains of family dynamics/ status and social role expectations in both our ethnographic sample and among the Western participants. We discuss the implications of this work and directions for future research. Keywords: affines, kin, in-laws, cooperation, conflict, pair-bonds AFFINAL CONFLICT 3 Mother-in-law daughter-in-law conflict: An evolutionary perspective, ethnographic review, and report of empirical data from the United States 1. Introduction Unlike most other social animals, humans form enduring relationships with the kin of their long-term mates. These relationships are referred to with terms like “in-laws” or “affines”, which at once signal kinship through marriage while also differentiating these relationships from those with genetic kin. As a result of long-term pair-bonding, marriage patterns, and extensive investment in offspring by parents as well as other kin, humans often live with and have ongoing interactions and relationships with their affines1 (D. E. Brown, 1991). Despite the strong emphases on both kinship bonds (Ackerman et al., 2007; Eberhard, 1975; Hamilton, 1964; Ko et al., 2020; Koster et al., 2019; Lieberman et al., 2007) and mating relationships (David M. Buss, 1985, 1989; David M. Buss & Barnes, 1986; D. M. Buss, 2017; D. M. Buss & Schmitt, 1993; Gangestad & Simpson, 2000; Symons, 1979) in evolutionary social science, there has been surprisingly little quantitative examination of the psychology bearing on relationships at the intersection of these foci; that is, on relationships among affines. Evolutionary-minded work on affinal relationships has been primarily descriptive and has primarily investigated the positive side of in-law relationships, specifically the ways in which affinal relationships are cooperative and beneficial for both parties (Dyble et al., 2018; Hrdy, 2007; Macfarlan et al., 2018; Willführ et al., 2018). However, conflict is also a central feature of 1 Technically speaking, some other species also have affines. For example, species that live in larger kin-based groups are more likely to have interactions with their affinal kin. Known dispersal patterns across non-human primate species are helpful in determining the kin relationships a focal individual has with others in their group, e.g., genetic vs. affinal, matrilineal vs. patrilineal. Among human populations, however, studying these relationships is potentially more complicated given that humans do not have universal dispersal patterns: sometimes females leave their natal groups (Ember, 1978; Marlowe, 2004; Murdock, 1967; Rodseth et al., 1991; Seielstad et al., 1998), other times males leave their natal groups (Ember, 1975; Murdock, 1949; Turnbull, 1976), and sometimes both sexes leave their natal groups (Koenig & Borries, 2012; Kramer et al., 2017; Marlowe, 2003). Additionally, affinal relationships can take different shapes across cultures due to differences in socioecological variables and other cultural factors, such as traditional marriage practices, inheritance rules, and descent tracing. AFFINAL CONFLICT 4 affinal relationships. For example, work in evolutionary anthropology suggests that child survivorship and mortality are influenced by female cooperation and conflict over resources and child care (Kaptijn et al., 2010; Sheppard & Sear, 2016; Voland & Beise, 2002, 2005)(Voland & Beise, 2002, 2005)owever, even in these papers, the focus of the papers is on the calculus behind female cooperation and conflict within families and its influence on long-term reproductive behavior (Ruth Mace, 2013; Strassmann, 2011) as opposed to the psychological experience of female cooperation and conflict within families. In this paper, we build off of this foundational work to focus on the experience and perceptions of cooperation and conflict, as these proximate factors should influence the ultimate reproductive outcomes, childhood survival, and relationships within the family unit. Outside of the evolutionary social science, other disciplines have made headway towards understanding the mother- and daughter-in-law dynamic. For example, across cultures, mothers-in-law are perceived to be “distant” and perceived less positively than mothers in relationships with their daughters-in-law (Adler et al., 1989), mothers-in-law experience more strained relationships with their daughters-in-law following the birth of a grandchild (Fischer, 1983), and mothers-in-law also often are faced with an unequal relationship power dynamic that causes strife in the relationship (Linn & Breslerman, 1996). In addition, mothers- and daughters- in-law generally have differences in goals, values, and communication styles (which we would argue also stem from differences in fitness-linked outcomes). When mother- and daughter-in- law relationships are successful, it is generally attributed to daughters-in-law being compliant to their mothers-in-law’s demands (Jackson & Berg-Cross, 1988). However, what is not addressed in these articles is why the mother- and daughter-in-law relationship has these negative and conflictual features. This is why an evolutionary perspective is necessary for understanding the ultimate reasons for cooperation and conflict in the mother- and daughter-in-law relationship. In this paper, we further develop the evolutionary logic behind in-law cooperation and conflict, arguing for the presence of conflict in affinal relationships. To do this, we present AFFINAL CONFLICT 5 evidence from ethnographic literature suggesting that conflict among affines is likely to be a human universal, and we also report findings from empirical data collected in a modern western population showing that both cooperation and conflict are components of relationships with in- laws. In sum, we find some support for our proposition that affinal conflict--and here, specifically--mother- and daughter-in-law conflict--is common across societies, and we suggest that this is a rich and understudied area for research on familial relationships in evolutionary perspective. 1.1 Genetic conflict might explain differences in cooperation and conflict. How do affinal relationships differ from relationships with biological kin? Hamilton’s (1964) rule is often used to explain cooperative behavior with biological kin because such cooperation can increase one’s inclusive fitness and also cause kin to feel stake in another’s welfare and survival (Roberts, 2005). We see examples of this in the non-human animal literature, for example, where older females signal that a predator is near, revealing their location and sometimes sacrificing their lives, in order to warn the group that danger is near (Sherman, 1977). Ultimately this stake in another’s welfare is caused by genes shared between the individual and their kin (i.e., inclusive fitness). But what about when two individuals have no genes in common? For example, while mothers and fathers are not closely related2, they still cooperate and share a stake in the survival of any shared offspring (Burton-Chellew & Dunbar, 2011; Dow, 1984; Hughes, 1988), creating interdependence between family members (Aktipis et al., 2018; Barclay, 2020; Sznycer et al., 2020). Such cooperation was almost certainly prevalent in the human ancestral past as well. At the same time, the lack of shared genes -- along with other fitness-linked asymmetries (e.g., age and sex differences in potential future reproductive output and preferred mating 2 In this paper, we are exclusively talking about relationships between