The evolution of parent–offspring conflict over mate choice

Parental Interference in Offspring's Mate Choice: Sets of Actions and Counteractions Based on Both Perspectives

Mate choice in humans is specific by the involvement of kin both in partner choice and in the functioning of the relationship. The influence of relatives ranges from providing advice all the way to arranged marriages. Existing research so far tended to map neither the actual parental interventions and further reactions (counteractions) nor the independently pursued behavior (actions) by which the offspring or their partners assert their interests. This study identified such sets of behaviors through semi-structured individual interviews with members of 20 dyads of adult offspring and their biological parents (five son-mother, five son-father, five daughter-mother, and five daughter-father dyads). Thematic analysis revealed sets of parental actions aimed at the offspring, their partners, and the couple as a whole, as well as further counteractions (reactions to parental interference) and independently pursued behavior (actions) of the offspring and their partners aimed at the parents in the context of the offspring's previous or current relationship. Our findings showed that parental interference differed depending on the recipient: toward the couple were applied mainly indirect and supportive parental actions, whereas when facing their offspring or offspring's partner, parents' actions were more direct and disruptive. Our results thus indicate the importance of reporting about actual interactions which differ from the hypothetical settings used in prior studies by lower intensity. Moreover, by interviewing both members of dyads, we expanded the sets of actions and counteractions identified by prior studies and managed to limit self-reporting bias.

Behavioral Ecology of the Family: Harnessing Theory to Better Understand Variation in Human Families

Researchers across the social sciences have long been interested in families. How people make decisions such as who to marry, when to have a baby, how big or small a family to have, or whether to stay with a partner or stray are questions that continue to interest economists, sociologists, demographers, and anthropologists. Human families vary across the globe; different cultures have different marriage practices, different ideas about who raises children, and even different notions of what a family is. Human behavioral ecology is a branch of anthropology that is particularly interested in cultural variation of family systems and how these differences impact upon the people that inhabit them; the children, parents, grandparents. It draws on evolutionary theory to direct research and generate testable hypotheses to uncover how different ecologies, including social contexts, can explain diversity in families. In this Special Issue on the behavioral ecology of the family, we have collated a selection of papers that showcase just how useful this framework is for understanding cultural variation in families, which we hope will convince other social scientists interested in family research to draw upon evolutionary and ecological insight in their own work.

Married Too Young? The Behavioral Ecology of ‘Child Marriage’

For girls and women, marriage under 18 years is commonplace in many low-income nations today and was culturally widespread historically. Global health campaigns refer to marriage below this threshold as ‘child marriage’ and increasingly aim for its universal eradication, citing its apparent negative wellbeing consequences. Here, we outline and evaluate four alternative hypotheses for the persistence of early marriage, despite its associations with poor wellbeing, arising from the theoretical framework of human behavioral ecology. First, early marriage may be adaptive (e.g., it maximizes reproductive success), even if detrimental to wellbeing, when life expectancy is short. Second, parent–offspring conflict may explain early marriage, with parents profiting economically at the expense of their daughter’s best interests. Third, early marriage may be explained by intergenerational conflict, whereby girls marry young to emancipate themselves from continued labor within natal households. Finally, both daughters and parents from relatively disadvantaged backgrounds favor early marriage as a ‘best of a bad job strategy’ when it represents the best option given a lack of feasible alternatives. The explanatory power of each hypothesis is context-dependent, highlighting the complex drivers of life history transitions and reinforcing the need for context-specific policies addressing the vulnerabilities of adolescence worldwide.

Evolutionary Mismatch in Mating

Evolutionary mismatch concepts are being fruitfully employed in a number of research domains, including medicine, health, and human cognition and behavior to generate novel hypotheses and better understand existing findings. We contend that research on human mating will benefit from explicitly addressing both the evolutionary mismatch of the people we study and the evolutionary mismatch of people conducting the research. We identified nine mismatch characteristics important to the study of human mating and reviewed the literature related to each of these characteristics. Many of the people we study are: exposed to social media, in temporary relationships, relocatable, autonomous in their mating decisions, nulliparous, in groups that are socially segmented, in an educational setting, confronted with lots of options, and young. We applied mismatch concepts to each characteristic to illustrate the importance of incorporating mismatch into this research area. Our aim in this paper is not to identify all potential mismatch effects in mating research, nor to challenge or disqualify existing data. Rather, we demonstrate principled ways of thinking about evolutionary mismatch in order to propel progress in mating research. We show how attending to the potential effects of mismatch can help us refine our theoretical and methodological approaches and deepen our understanding of existing patterns in the empirical record. We conclude with specific recommendations about how to include consideration of evolutionary mismatch into research on human mating.

Parent-offspring conflict unlikely to explain 'child marriage' in northwestern Tanzania

Approximately 40% of women in sub-Saharan Africa marry before their eighteenth birthday¹. Within the international development sector, this phenomenon is referred to as 'child marriage', widely equated to forced marriage, and recognized as damaging to multiple dimensions of female well-being^1,2. An escalating global campaign to end early marriage typically assumes that its high prevalence is driven by a conflict of interests between parents and daughters, with parents coercing daughters to marry early for the parents' economic benefit³. However, a parent-offspring conflict model of early marriage has not been explicitly tested. Here we present a study of marriage transitions in rural Tanzania, where marriage before or just after 18 years of age is normative. Consistent with parental coercion, we find that bridewealth transfers are highest for younger brides. However, autonomy in partner choice is very common at all ages, relationships between age at marriage and female well-being are largely equivocal, and women who marry early achieve relatively higher reproductive success. We conclude that, in contexts in which adolescents have autonomy in marriage choices and in which marriage promotes economic and social security, early marriage may be better understood as serving the strategic interests of both parents and daughters.

Parent-offspring conflict over mate choice: An experimental study in China

Both parents and offspring have evolved mating preferences that enable them to select mates and children-in-law to maximize their inclusive fitness. The theory of parent-offspring conflict predicts that preferences for potential mates may differ between parents and offspring: individuals are expected to value biological quality more in their own mates than in their offspring's mates and to value investment potential more in their offspring's mates than in their own mates. We tested this hypothesis in China using a naturalistic 'marriage market' where parents actively search for marital partners for their offspring. Parents gather at a public park to advertise the characteristics of their adult children, looking for a potential son or daughter-in-law. We presented 589 parents and young adults from the city of Kunming (Yunnan, China) with hypothetical mating candidates varying in their levels of income (proxy for investment potential) and physical attractiveness (proxy for biological quality). We found some evidence of a parent-offspring conflict over mate choice, but only in the case of daughters, who evaluated physical attractiveness as more important than parents. We also found an effect of the mating candidate's sex, as physical attractiveness was deemed more valuable in a female potential mate by parents and offspring alike.

Selfish Pups: Weaning Conflict and Milk Theft in Free-Ranging Dogs

Parent-offspring conflict theory predicts the emergence of weaning conflict between a mother and her offspring arising from skewed relatedness benefits. Empirical observations of weaning conflict have not been carried out in canids. In a field-based study on free-ranging dogs we observed that nursing/suckling bout durations decrease, proportion of mother-initiated nursing bouts decrease and mother-initiated nursing/suckling terminations increase with pup age. We identified the 7^th - 13^th week period of pup age as the zone of conflict between the mother and her pups, beyond which suckling solicitations cease, and before which suckling refusals are few. We also report for the first time milk theft by pups who take advantage of the presence of multiple lactating females, due to the promiscuous mating system of the dogs. This behaviour, though apparently disadvantageous for the mothers, is perhaps adaptive for the dogs in the face of high mortality and competition for resources.

Body Height Preferences and Actual Dimorphism in Stature between Partners in Two Non-Western Societies (Hadza and Tsimane')

Body height influences human mate preferences and choice. A typical finding in Western societies is that women prefer men who are taller than themselves and, equivalently, men prefer women who are shorter than themselves. However, recent reports in non-Western societies (e.g., the Himba in Namibia) challenge the view on the universality of such preferences. Here we report on male and female height preferences in two non-Western populations—the Hadza (Tanzania) and the Tsimane' (Bolivia)—and the relationships between body height preferences and the height of actual partners. In the Hadza, most individuals preferred a sexual dimorphism in stature (SDS) with the man being much taller than the woman. Preferences for SDS and actual partner SDS were positively and significantly correlated in both men and women, suggesting that people who preferred larger height differences also had larger height differences with their partners. In the Tsimane', the majority of men preferred an SDS with the man being taller than the woman, but women did not show such a preference. Unlike in the Hadza, SDS preference was not significantly correlated to actual partner SDS. We conclude that patterns of height preferences and choices in the Hadza and Tsimane' are different than those observed in Western societies, and discuss possible causes for the observed differences between non-Western and Western societies.

Selfish mothers indeed! Resource-dependent conflict over extended parental care in free-ranging dogs

Parent-offspring conflict (POC) theory provides an interesting premise for understanding social dynamics in facultatively social species. In free-ranging dogs, mothers increase conflict over extended parental care with their pups beyond the weaning stage. In this study, we investigated whether resource quality affects POC in the dogs that typically live in a highly competitive environment as scavengers. We built a theoretical model to predict the alternative options available to the mother in the context of food sharing with her pups when protein-rich food (meat) is provided, as compared to carbohydrate-rich food (biscuits). We fit the mothers' response from experimental data to the model and show that the mothers choose a selfish strategy, which can in turn ensure higher lifetime reproductive success, while depriving the current litter access to better resources. These results have interesting implications for understanding the social dynamics of the dogs, and the emergence of facultative sociality in a species that evolved from strongly social ancestors. We speculate that the tendency of increased conflict in resource-rich conditions might have driven the process of domestication in the ancestors of dogs which defected from their groups in favour of richer resources around human settlements.

Parent-Offspring Conflict Over Mating : Domains of Agreement and Disagreement

Evolutionary reasoning indicates that certain traits are more beneficial when they are found in a mate than in a son- or a daughter-in-law, while other traits are more beneficial when they are found in a son- or a daughter-in-law than in a mate. This translates into different evolutionary pressures exercised on in-law and mate preferences driving them to diverge. The purpose of this research is to identify the domains over which in-law and mate choice is exercised, and following this, to identify the areas of agreement and disagreement in these domains. In particular, using an extensive sample of parents (N = 1,717), Study 1 identifies 10 domains over which mate and in-law choice is exercised. Study 2 employs a sample of families (N = 541) in order to compare the preferences of parents with the preferences of their children. It is found that in-law and mate preferences diverge over several domains including good looks, personality, and family background.

My Parents Know Best: No Mating With Members From Other Ethnic Groups

This study examined the opposition against out-group mating and the attitude towards parental influence on mate choice among 107 Dutch, 69 Moroccan, and 69 Turkish participants aged between 15 and 25. The level of preferred parental influence on mate choice was considerably higher among the Turks and Moroccans than among the Dutch, but females in both ethnic groups were less in favor of parental influence on mate choice than males were. Overall, males showed a higher opposition against interethnic dating than females did, and the Turks showed a higher level of opposition to interethnic mating than both the Moroccans and the Dutch. In addition, the effect of opposition against interethnic mating on preferred parental influence on mate choice was especially pronounced among the Turks, somewhat less so among the Moroccans, and least strong among the Dutch. Especially young males with a Turkish and Moroccan background seem to hold on to the values of the cultures they come from, and particularly Turkish immigrants seem keen on keeping the cohesion of their ethnic group intact by opposing interethnic dating, and by favoring parental influence on mate choice as a way to achieve this goal.

Intergenerational conflicts may help explain parental absence effects on reproductive timing: a model of age at first birth in humans

Background. Parental absences in childhood are often associated with accelerated reproductive maturity in humans. These results are counterintuitive for evolutionary social scientists because reductions in parental investment should be detrimental for offspring, but earlier reproduction is generally associated with higher fitness. In this paper we discuss a neglected hypothesis that early reproduction is often associated with parental absence because it decreases the average relatedness of a developing child to her future siblings. Family members often help each other reproduce, meaning that parents and offspring may find themselves in competition over reproductive opportunities. In these intergenerational negotiations offspring will have less incentive to help the remaining parent rear future half-siblings relative to beginning reproduction themselves.

Method. We illustrate this “intergenerational conflict hypothesis” with a formal game-theoretic model.

Results. We show that when resources constrain reproductive opportunities within the family, parents will generally win reproductive conflicts with their offspring, i.e., they will produce more children of their own and therefore delay existing offsprings’ reproduction. This is due to the asymmetric relatedness between grandparents and grandchildren (r = .25), compared to siblings (r = 0.5), resulting in greater incentives for older siblings to help rear younger siblings than for grandparents to help rear grandchildren. However, if a parent loses or replaces their partner, the conflict between the parent and offspring becomes symmetric since half siblings are as related to one another as grandparents are to grandchildren. This means that the offspring stand to gain more from earlier reproduction when their remaining parent would produce half, rather than full, siblings. We further show that if parents senesce in a way that decreases the quality of their infant relative to their offspring’s infant, the intergenerational conflict can shift to favor the younger generation.