The puzzle of monogamous marriage

Human Reproductive Egalitarianism: A Catalyst for the Evolution of Personality Traits

The human, species-typical reproductive system is distinctive and unique among the great apes. It involves pair-bonding and long-term mating as well as male investment in both mate and offspring. Studies have demonstrated that this mating system produces the lowest male reproductive skew known in primates as well as in mammals generally which entails the lowest level of reproductive failure among human males compared to other primate/mammalian species. It is argued that this low reproductive skew leads to an increase in the effective population size and to a greater diversification/variation in personality and behavioural traits in the population compared to other species. The implications of this Reproductive Egalitarian Model for human mating are discussed with regard to the emergence of human personality traits, social complexity, division of labour and risk of mental disorder.

Little evidence that nonmonogamous family structures are detrimental to children's well-being in Mpimbwe, Tanzania

Nuclear family structures are often thought to be essential for the well-being of children. Divorce, the loss of either biological parent, the presence of step-parents, and the practice of polygynous marriage have all been claimed to negatively impact child well-being. However, empirical research on these topics has been limited by the routine use of cross-regional and cross-sectional databases. Cross-regional data render research vulnerable to the ecological inference fallacy, and cross-sectional data prevent assessment of age-specific impacts of time-varying family-structure variables. When longitudinal data are available, they tend to be drawn from Western/urban contexts. Detailed data on family structure and children's well-being are rarely collected in more marginalized communities. In many rural and traditional communities, nonnuclear family structures are indeed prevalent and viewed as socially permissible-and, as such, may have different impacts on children's well-being than in Western contexts. Here, we draw on a detailed, longitudinal dataset from a 20-y prospective study in rural Tanzania, where polygyny and serial monogamy are common. We analyze survival outcomes for 3,693 children born between 1931 and 2014, growth outcomes for 881 children born between 1976 and 2014, and educational outcomes for 1,370 children born between 1976 and 2014. Our analyses indicate that monogamous marriage is not consistently associated with better outcomes for children-contrary to some popular and public health perspectives on human family structure.

Why religion and spirituality are important in human biological research

The study of human biology includes exploration of all the genetic and environmental influences on human variation and life history, including impacts of sociocultural and physical environments. Religious practice and spirituality may be one of these influences. There are more than 5.8 billion religiously affiliated adults and children, accounting for 84% of the world's 6.9 billion people. Furthermore, 70% of Americans consider themselves spiritual in some way, including 22% who do not consider themselves religious, and the numbers for Europe are lower but proportionally similar. Such a high rate of religious affiliation and spiritual belief suggests that religion and spirituality could be sociocultural influences on human variation, but human biologists have scarcely attended to their impacts, as indicated by the limited numbers of relevant articles in the two flagship human biology journals. In this article, we discuss why human biologists may have overlooked this important force for human variability and highlight foundational work from human biology and other disciplines that can give our colleagues directions forward. We review the impacts of religion and spirituality at population and individual levels and call for human biologists to attend to the many aspects of religion and spirituality that can impact human biology and are much more than simply influences of denominational affiliation.

Examining the Role of Mononormative Beliefs, Stigma, and Internalized Consensual Non-Monogamy Negativity for Dehumanization

Interest in consensually non-monogamous (CNM) relationships has been increasing in the general population in recent years. However, given the cultural dominance of monogamy and the normative expectations often imposed through socialization (i.e., mononormativity), people in CNM relationships may experience negativity, which can become internalized and harm their individual and relationship health. The present study investigated if mononormativity beliefs and CNM relationship stigma were associated with more dehumanization and if internalized CNM negativity was an underlying mechanism for these associations. Results showed that participants who endorsed more mononormative beliefs and CNM relationship stigma also reported more internalized CNM negativity. In turn, participants who experienced more internalized CNM negativity attributed more negative (vs. positive) emotions to themselves and treated their partners as more immature, unrefined, exploitable, and emotionless. These results show that mononormativity and internalized negativity can shape the attitudes, perceptions, and behaviors of CNM individuals toward themselves and their partners.

A Narrative Review of the Dichotomy Between the Social Views of Non-Monogamy and the Experiences of Consensual Non-Monogamous People

Monogamy is deeply rooted in most Western societies, shaping how people construe and behave in romantic relationships. These normative views facilitate the emergence of negative perceptions and evaluations when people choose not to adhere to mononormativity. Even though people in consensual non-monogamous (CNM) relationships are targets of stigmatization, research shows a dichotomy between these negative views and the relational experiences of CNM people. Indeed, people in CNM and monogamous relationships have comparable relationship functioning and quality and struggle with similar relationship problems. One of the differences is that CNM relationships afford people to explore their sexuality and fulfill their needs with multiple partners, without agreed-upon extradyadic behavior being perceived as infidelity or having deleterious consequences to relationship maintenance. These positive experiences notwithstanding, CNM people are continuously pressured by mononormativity and stigmatization, increasing the risk of internalized CNM negativity and worse personal and relational outcomes. One possible way to counteract CNM stigmatization and improve the lives of CNM people is by changing discourses surrounding non-monogamy and improving acceptance, not only in professional settings but also in the general population. Another strategy is to understand how the relationship beliefs and scripts of younger generations can help promote more inclusive and diverse societies.

Sex ratios and gender norms: why both are needed to understand sexual conflict in humans

Sexual conflict theory has been successfully applied to predict how in non-human animal populations, sex ratios can lead to conflicting reproductive interests of females and males and affect their bargaining positions in resolving such conflicts of interests. Recently this theory has been extended to understand the resolution of sexual conflict in humans, but with mixed success. We argue that an underappreciation of the complex relationship between gender norms and sex ratios has hampered a successful understanding of sexual conflict in humans. In this paper, we review and expand upon existing theory to increase its applicability to humans, where gender norms regulate sex ratio effects on sexual conflict. Gender norms constrain who is on the marriage market and how they are valued, and may affect reproductive decision-making power. Gender norms can also directly affect sex ratios, and we hypothesize that they structure how individuals respond to market value gained or lost through biased sex ratios. Importantly, gender norms are in part a product of women's and men's sometimes conflicting reproductive interests, but these norms are also subject to other evolutionary processes. An integration of sexual conflict theory and cultural evolutionary theory is required to allow for a full understanding of sexual conflict in humans.

Ideological Mate-guarding: Sexual Jealousy and Mating Strategy Predict Support for Female Honor

Feminine honor dictates that women should cultivate a reputation for sexual purity via behaviors such as dressing modestly and maintaining virginity before marriage. The dominant explanation for people's support for feminine honor is that female infidelity threatens male partners' honor. Beyond this, the literature affords little understanding of the evolutionary and psychological origins of feminine honor. We propose that feminine honor functions as an ideological form of mate guarding that is shaped by sexual jealousy and mating strategy. Two correlational studies (N  =  892) revealed support for predictions derived from this ideological mate-guarding account. In Study 1, dispositional jealousy and mating strategy (more monogamous orientation) predicted male participants' support for a mate's (especially a long-term mate's) feminine honor. Moving beyond mate preferences, in Study 2 male and female participants' dispositional jealousy and mating strategy predicted support for feminine honor of women in general. Results applied beyond masculine honor norms, religiosity, political conservativism, and age. These findings enhance the understanding of the origins and maintenance of feminine honor and related norms and ideologies that enable control over women's socio-sexual behavior.

Male-male relationships in chimpanzees and the evolution of human pair bonds

The evolution of monogamy has been a central question in biological anthropology. An important avenue of research has been comparisons across "socially monogamous" mammals, but such comparisons are inappropriate for understanding human behavior because humans are not "pair living" and are only sometimes "monogamous." It is the "pair bond" between reproductive partners that is characteristic of humans and has been considered unique to our lineage. I argue that pair bonds have been overlooked in one of our closest living relatives, chimpanzees. These pair bonds are not between mates but between male "friends" who exhibit enduring and emotional social bonds. The presence of such bonds in male-male chimpanzees raises the possibility that pair bonds emerged earlier in our evolutionary history. I suggest pair bonds first arose as "friendships" and only later, in the human lineage, were present between mates. The mechanisms for these bonds were co-opted for male-female bonds in humans.

Reproductive inequality in humans and other mammals

To address claims of human exceptionalism, we determine where humans fit within the greater mammalian distribution of reproductive inequality. We show that humans exhibit lower reproductive skew (i.e., inequality in the number of surviving offspring) among males and smaller sex differences in reproductive skew than most other mammals, while nevertheless falling within the mammalian range. Additionally, female reproductive skew is higher in polygynous human populations than in polygynous nonhumans mammals on average. This patterning of skew can be attributed in part to the prevalence of monogamy in humans compared to the predominance of polygyny in nonhuman mammals, to the limited degree of polygyny in the human societies that practice it, and to the importance of unequally held rival resources to women's fitness. The muted reproductive inequality observed in humans appears to be linked to several unusual characteristics of our species-including high levels of cooperation among males, high dependence on unequally held rival resources, complementarities between maternal and paternal investment, as well as social and legal institutions that enforce monogamous norms.

The Evolution of Inclusive Folk-Biological Labels and the Cultural Maintenance of Meaning

How is word meaning established, and how do individuals acquire it? What ensures the uniform understanding of word meaning in a linguistic community? In this paper I draw from cultural attraction theory and use folk biology as an example domain and address these questions by treating meaning acquisition as an inferential process. I show that significant variation exists in how individuals understand the meaning of inclusive biological labels such as "plant" and "animal" due to variation in their salience in contemporary ethnic minority groups in southwest China, and I present historical textual evidence that the meaning of inclusive terms is often unstable but can be sustained by such cultural institutions as religion and education, which provide situations in which the meaning of linguistic labels can be unambiguously inferred.

Norm violations and punishments across human societies

Punishments for norm violations are hypothesised to be a crucial component of the maintenance of cooperation in humans but are rarely studied from a comparative perspective. We investigated the degree to which punishment systems were correlated with socioecology and cultural history. We took data from the Standard Cross-Cultural Sample database and coded ethnographic documents from a sample of 131 largely non-industrial societies. We recorded whether punishment for norm violations concerned adultery, religion, food, rape or war cowardice and whether sanctions were reputational, physical, material or execution. We used Bayesian phylogenetic regression modelling to test for culture-level covariation. We found little evidence of phylogenetic signals in evidence for punishment types, suggesting that punishment systems change relatively quickly over cultural evolutionary history. We found evidence that reputational punishment was associated with egalitarianism and the absence of food storage; material punishment was associated with the presence of food storage; physical punishment was moderately associated with greater dependence on hunting; and execution punishment was moderately associated with social stratification. Taken together, our results suggest that the role and kind of punishment vary both by the severity of the norm violation, but also by the specific socio-economic system of the society.

Men. Male-biased sex ratios and masculinity norms: evidence from Australia's colonial past

We document the historical roots and contemporary consequences of masculinity norms-beliefs about the proper conduct of men. We exploit a natural experiment in which convict transportation in the 18 th and 19 th centuries created a variegated spatial pattern of sex ratios across Australia. We show that in areas with heavily male-biased convict populations, relatively more men volunteered for World War I about a century later. Even at present these areas remain characterized by more violence, higher rates of male suicide and other forms of preventable male mortality, and more male-stereotypical occupational segregation. Moreover, in these historically male-biased areas, more Australians recently voted against same-sex marriage and boys-but not girls-are more likely to be bullied in school. We interpret these results as manifestations of masculinity norms that emerged due to intense local male-male competition. Once established, masculinity norms persisted over time through family socialization as well as peer socialization in schools.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10887-023-09223-x.

Dual Mating Strategies Observed in Male Clients of Female Sex Workers

Humans have a complex and dynamic mating system, and there is evidence that our modern sexual preferences stem from evolutionary pressures. In the current paper we explore male use of a dual mating strategy: simultaneously pursuing both a long-term relationship (pair-bonding) as well as short-term, extra-pair copulations (variety-seeking). The primary constraint on such sexual pursuits is partner preferences, which can limit male behavior and hence cloud inferences about male preferences. The aim of this study was to investigate heterosexual male mating preferences when largely unconstrained by female partner preferences. In service of this goal, female full-service sex workers (N = 6) were surveyed on the traits and behaviors of their male clients (N = 516) and iterative cluster analysis was used to identify male mating typologies. Two clusters emerged: clients seeking a pair-bonding experience and clients seeking a variety experience. Results also suggested that romantically committed men were more likely to seek a variety experience than a relationship experience. We conclude that men desire both pair-bonding and sexual variety, and that their preference for one might be predicted by fulfilment of the other. These findings have implications for relationships, providing insight into motivations for male infidelity.

An evolutionary case for polygyny to counter demographic collapse

Sex ratio theory suggests why mating practices have become dysfunctional in the West and other regions. Spain, Japan, and over 20 other nations are on course to have their populations halved by 2100, dramatically aging their citizenry. Experts and opinion makers warn that a demographic collapse cannot be absorbed by our current social order; Elon Musk proclaims this to be "the biggest threat to human civilization." Statistics from the Nordic countries-the world's most gender-equal region-indicate that subjective perceptions of the sex ratio in modern environments drive singledom and low reproduction. Scandinavia has the world's highest occurrence of one-person households: 43-46%. In the past decade, the Norwegian fertility rate dropped from 2.0 to 1.5. Sex ratio studies suggest that women's perception of there being few acceptable partners activates a polygynous mindset, which in prosperous, monogamous societies drives promiscuity to the detriment of pair-bonding. More than 6 million years of hominin evolution under promiscuous, polygynous, and monogamous regimes shaped mate preferences that evoke different cultural and behavioral responses as environments change. The Church's imposition of lifelong monogamy contributed to the emergence of the modern world, but if this world's gender-equal societies no longer motivate reproduction, being more open to polygyny could be worth considering as a means for increasing fertility. This article makes this case by exploring hominin mating from our last common ancestor with chimpanzees-through the genus Homo's forager and agricultural periods-to modern Scandinavians. In the past millennium, mating practices have coevolved with the emergence of modernity, necessitating frequent cultural updates. An evolutionary analysis of Nordic works of literature illuminates the ways in which ideological narratives influence reproductive norms. The insights gleaned are considered in the context of people's perceived sex ratio.

Understanding the sex inequality in childlessness: an approach using Swedish register data

In most countries, men are more likely to be childless than women. Understanding how this inequality arises is important given the significance of parenthood for individuals' lives. The objective of this study was to explore how three prominent explanations for sex inequalities in childlessness relate to the Sex Gap in Childlessness (SGC) in Sweden. The three explanations examined were sex ratio imbalance (more men than women), mismeasurement of fatherhood (inequalities in registration) and partnership differences (inequality in multi-partner fertility). Administrative register data for cohorts born in 1945-1974 were used. The population was restricted to men and women who were born in Sweden or arrived prior to the age of 15, and all registered childbearing partnerships were examined. To explore the possible significance of the three explanations, counter-factual standardization was used. Of the three explanations examined, the population sex ratio had the largest positive impact on the SGC, while multi-partner fertility had a negative impact. The results show that inequalities in the sex ratio can explain about 20-34% of the SGC depending on cohort. Inequalities in registration of fathers explain about 9-24% of the SGC depending on cohort. Finally, results show that women are slightly more likely to have multiple partners, and that this behaviour has a substantial minimizing effect on the SGC (minimizing it by 6-65%). To the authors' knowledge this was the first paper to estimate the scope of the impacts of these three mechanisms on the SGC. Differences in multi-partner fertility have in many instances been used as an explanation for men's higher childlessness. This study shows that women have slightly more childbearing partners than men, and that this actually leads to a smaller SGC in the studied population.

Integrating economic and evolutionary approaches to polygynous marriage

We outline the potential for integrating economic and evolutionary approaches to marriage and the family. Our broad argument is that the approaches share a concern for competition. Evolutionary scholars are concerned with the fitness consequences of competition and economists are centrally concerned with the nature of competition: how the allocation of scarce resources is mediated by potentially complex forms of social interaction and conflicts of interest. We illustrate our argument by focusing on conceptual and empirical approaches to a topic of interest to economists and evolutionary scholars: polygynous marriage. In comparing conceptual approaches, we distinguish between those that emphasise the physical environment and those that emphasise the social environment. We discuss some advantages of analysing marriage through the lens of competitive markets, and outline some of the ways that economists analyse the emergence of rules governing the family. In discussing empirical approaches to polygynous marriage, we describe how a concern for informing contemporary policy leads economists to focus on the consequences of polygyny, and in particular we describe some of the ways in which economists attempt to distinguish causal effects from selection effects.

The prosociality of married people: Evidence from a large multinational sample

Single people are more likely to die from COVID-19. Here we study whether this higher death rate could be partly explained by differences in compliance with protective health measures against COVID-19 between single and married people, and the drivers of this marital compliance gap. Data collected from 46,450 respondents in 67 countries reveal that married people are more likely to comply with protective measures than single people. This marital gap in compliance is higher for men (approximately 5%) than for women (approximately 2%). These results are robust across a large range of countries and independent of country level differences with respect to culture, values or infection rates. Prosocial characteristics linked to morality and social belonging explain more than 38% of the marital gap, while individual risk perceptions play a minor role. These findings help explain single people's and particularly single men's greater vulnerability to COVID-19, which in turn can be leveraged to improve the effectiveness of international public policy campaigns aimed at promoting protective health measures.

Moral disciplining: The cognitive and evolutionary foundations of puritanical morality

Why do many societies moralize apparently harmless pleasures, such as lust, gluttony, alcohol, drugs, and even music and dance? Why do they erect temperance, asceticism, sobriety, modesty, and piety as cardinal moral virtues? According to existing theories, this puritanical morality cannot be reduced to concerns for harm and fairness: It must emerge from cognitive systems that did not evolve for cooperation (e.g., disgust-based "purity" concerns). Here, we argue that, despite appearances, puritanical morality is no exception to the cooperative function of moral cognition. It emerges in response to a key feature of cooperation, namely that cooperation is (ultimately) a long-term strategy, requiring (proximately) the self-control of appetites for immediate gratification. Puritanical moralizations condemn behaviors which, although inherently harmless, are perceived as indirectly facilitating uncooperative behaviors, by impairing the self-control required to refrain from cheating. Drinking, drugs, immodest clothing, and unruly music and dance are condemned as stimulating short-term impulses, thus facilitating uncooperative behaviors (e.g., violence, adultery, free-riding). Overindulgence in harmless bodily pleasures (e.g., masturbation, gluttony) is perceived as making people slave to their urges, thus altering abilities to resist future antisocial temptations. Daily self-discipline, ascetic temperance, and pious ritual observance are perceived as cultivating the self-control required to honor prosocial obligations. We review psychological, historical, and ethnographic evidence supporting this account. We use this theory to explain the fall of puritanism in western, educated, industrialized, rich, and democratic (WEIRD) societies, and discuss the cultural evolution of puritanical norms. Explaining puritanical norms does not require adding mechanisms unrelated to cooperation in our models of the moral mind.

Men are not aware of and do not respond to their female partner's fertility status: Evidence from a dyadic diary study of 384 couples

Understanding how human mating psychology is affected by changes in female cyclic fertility is informative for comprehending the evolution of human reproductive behavior. Based on differential selection pressures between the sexes, men are assumed to have evolved adaptations to notice women's within-cycle cues to fertility and show corresponding mate retention tactics to secure access to their female partners when fertile. However, previous studies suffered from methodological shortcomings and yielded inconsistent results. In a large, preregistered online dyadic diary study (384 heterosexual couples), we found no compelling evidence that men notice women's fertility status (as potentially reflected in women's attractiveness, sexual desire, or wish for contact with others) or display mid-cycle increases in mate retention tactics (jealousy, attention, wish for contact or sexual desire towards female partners). These results extend our current understanding of the evolution of women's concealed ovulation and oestrus, and suggest that both might have evolved independently.

Men are less religious in more gender-equal countries

Sex differences in religiosity are cross-culturally common and robust, yet it is unclear why sex differences in some cultures are larger than in others. Although women are more religious than men in most countries, religions frequently provide asymmetrical benefits to men at the expense of women. Two global analyses (51 countries and 74 countries) found that country-level gender equality was consistently and negatively associated with religiousness (i.e. religious attendance, reported importance of God and frequency of prayer) for men, more than for women, leading to a larger sex difference in religiousness in more gender-equal countries. Results were especially robust for religious attendance, and hold accounting for country-level wealth, as well as individuals' religious affiliation, the moralization of sexuality, age and education level. We interpret results through a rational choice lens, which assumes that people are more drawn to religion when it is consistent with their reproductive goals.

Phenotypic Signals of Sexual Selection and Fast Life History Dynamics for the Long-Term but Not Short-Term Mating

Mating patterns are crucial for understanding selection regimes in current populations and highly implicative for sexual selection and life history theory. However, empirical data on the relations between mating and reproductive outcomes in contemporary humans are lacking. In the present research we examined the sexual selection on mating (with an emphasis on Bateman's third parameter - the association between mating and reproductive success) and life history dynamics of mating by examining the relations between mating patterns and a comprehensive set of variables which determine human reproductive ecology. We conducted two studies (Study 1: N = 398, Study 2: N = 996, the sample was representative for participants' sex, age, region, and settlement size). The findings from these studies were mutually congruent and complementary. In general, the data suggested that short-term mating was unrelated or even negatively related to reproductive success. Conversely, long-term mating was positively associated with reproductive success (number of children in Study 1; number of children and grandchildren in Study 2) and there were indices that the beneficial role of long-term mating is more pronounced in males, which is in accordance with Bateman's third principle. Observed age of first reproduction mediated the link between long-term mating and number of children but only in male participants (Study 2). There were no clear indications of the position of the mating patterns in human life history trajectories; however, the obtained data suggested that long-term mating has some characteristics of fast life history dynamics. Findings are implicative for sexual selection and life history theory in humans.

The Cultural Evolution of Epistemic Practices : The Case of Divination

Although a substantial literature in anthropology and comparative religion explores divination across diverse societies and back into history, little research has integrated the older ethnographic and historical work with recent insights on human learning, cultural transmission, and cognitive science. Here we present evidence showing that divination practices are often best viewed as an epistemic technology, and we formally model the scenarios under which individuals may overestimate the efficacy of divination that contribute to its cultural omnipresence and historical persistence. We found that strong prior belief, underreporting of negative evidence, and misinferring belief from behavior can all contribute to biased and inaccurate beliefs about the effectiveness of epistemic technologies. We finally suggest how scientific epistemology, as it emerged in Western societies over the past few centuries, has influenced the importance and cultural centrality of divination practices.

Association of Marital Status in the Testing and Treatment of Sexually Transmitted Infections in the Emergency Department

Introduction Sexually transmitted infections (STIs) are frequently tested for and treated in the emergency department (ED). Age, race, and number of sexual partners are known risk factors for STIs. The objective of the current study was to examine marital status as it relates to testing and treating for STIs in the ED. Methods A database of 75,000 ED patient encounters from a single healthcare system in northeast Ohio between April 18, 2014, and March 7, 2017, was examined. All patients in the dataset underwent a urinalysis and urine culture or received STI testing in the ED. We performed Chi-square and multivariable regression analysis to examine the relationships between the patient's marital status and testing and treatment for STIs performed in the ED. Results There were 20,965 patient encounters where STI testing was performed and was analyzed. Patients were 9.1% (N=1,912) married, 86.6% (N=18,149) single, 4.0% (N=837) were neither married nor single, and 0.3% (N=67) with an unknown marital status. There were 7.1% (19/267) and 4.9% (12/267) of tested married men who were infected with gonorrhea and chlamydia, respectively, whereas only 0.4% (6/1,583) and 2.2% (35/1,588) of tested married women were infected with gonorrhea and chlamydia, respectively. Single men and women were both significantly more likely to have a positive test for gonorrhea and chlamydia compared to married men and women, respectively (P<0.001). Married men and women, compared to single men and women, respectively, were more likely to be given antibiotics for gonorrhea and chlamydia in the ED when the infection was present and not be given antibiotics for the infections when testing was negative (P<0.001). Single women (9.1%; 1,291/14,258) were more likely than married women (4.9%; 75/1,534) to have a positive test for trichomonas, but there were no significant differences between married (1.0%; 1/100) and single men (0.7%; 6/893). Conclusion Even when accounting for age and race, marital status can help predict infection with gonorrhea and chlamydia in the ED. The marital status could be considered by clinicians when risk stratifying patients regarding testing and treating for the diseases in the ED. Gonorrhea and chlamydia are much more common in single men and women and much less common in married persons. However, married men tested for gonorrhea and chlamydia were more than twice as likely to test positive for infection than married women. Married men and women were both more likely to be appropriately treated with antibiotics for gonorrhea and chlamydia in the ED (i.e., testing negative for infection and not receiving antibiotics or testing positive and receiving antibiotics) compared to non-married men and women. While trichomonas was more common in single women than married women, the infection was less common in men, and both married men and single men had similar rates of testing positive for the infection.

Sex differences in human mate preferences vary across sex ratios

A wide range of literature connects sex ratio and mating behaviours in non-human animals. However, research examining sex ratio and human mating is limited in scope. Prior work has examined the relationship between sex ratio and desire for short-term, uncommitted mating as well as outcomes such as marriage and divorce rates. Less empirical attention has been directed towards the relationship between sex ratio and mate preferences, despite the importance of mate preferences in the human mating literature. To address this gap, we examined sex ratio's relationship to the variation in preferences for attractiveness, resources, kindness, intelligence and health in a long-term mate across 45 countries (n = 14 487). We predicted that mate preferences would vary according to relative power of choice on the mating market, with increased power derived from having relatively few competitors and numerous potential mates. We found that each sex tended to report more demanding preferences for attractiveness and resources where the opposite sex was abundant, compared to where the opposite sex was scarce. This pattern dovetails with those found for mating strategies in humans and mate preferences across species, highlighting the importance of sex ratio for understanding variation in human mate preferences.

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.

Disparities in mothers' healthcare seeking behavior for common childhood morbidities in Ethiopia: based on nationally representative data

BACKGROUND

Childhood morbidities such as diarrhea and pneumonia are the leading causes of death in Ethiopia. Appropriate healthcare-seeking behavior of mothers for common childhood illnesses could prevent a significant number of these early deaths; however, little nation-wide research has been conducted in Ethiopia to assess mothers' healthcare-seeking behavior for their under five children.

METHODS

The study used the Ethiopian Demographic and Health Surveys (EDHS) data. The EDHS is a cross sectional survey conducted in 2016 on a nationally representative sample of 10,641 respondents. The main determinants of care-seeking during diarrhea and acute respiratory infection (ARI) episodes were assessed using multiple logistic regression analyses while adjusting for complex survey design.

RESULTS

Only 43% and 35% of households sought medical attention for their children in episodes of diarrhea and ARI, respectively, during a reference period of 2 weeks before the survey. The odds of seeking care for diarrhea are lower for non-working mothers versus working mothers. The likelihood of seeking care for diarrhea or ARI is higher for literate fathers compared to those with no education. The place of delivery for the child, receiving postnatal checkup and getting at least one immunization in the past determined the likelihood of seeking care for ARI, but not for diarrhea. The odds of seeking care are higher for both diarrhea and ARI among households that are headed by females and where mothers experienced Intimate Partner Violence (IPV) violence. Religion and types of family structure are also significant factors of seeking care for diarrhea episodes, but not for ARI.

CONCLUSIONS

The findings call for more coordinated efforts to ensure equitable access to health care services focusing on mothers living in deprived household environment. Strengthening partnerships with public facilities, private health care practitioners, and community-based organizations in rural areas would help further improve access to the services.

Compersion: When Jealousy-Inducing Situations Don't (Just) Induce Jealousy

Emotional reactions to a partner's extradyadic romantic interests are assumed to be negative and characterized by jealousy, an emotional state that arises over a perceived threat to one's relationship. Yet, reactions may also be positive, and involve compersion, or taking joy in one's partner's pleasure in other sexual and relational encounters. Although some have argued that compersion is the opposite of jealousy, research suggests that compersion and jealousy may not be opposing constructs, despite being treated this way in both theoretical and empirical research. Using a convenience sample of polyamorous (N = 3530) and monogamous (N = 1358) individuals, we draw on theories of jealousy, emotional ambivalence, and emotional forecasting to examine people's anticipated affective responses to hypothetical situations involving a partner's extradyadic relations and assess whether experience with having a partner engage in extradyadic relations was associated with anticipating less jealousy and more compersion. Results suggest that people in polyamorous relationships report less jealousy and more compersion with their partners, and that personal experience involving a partner's extradyadic romantic interests predicted more compersion and less jealousy, with experience predicting greater increases in compersion among monogamous than polyamorous participants. Finally, while anticipated compersion was associated with greater relationship satisfaction, neither jealousy nor ambivalence was associated with relationship satisfaction. These results further demonstrate that individuals can experience both positive and negative reactions to a partner's extradyadic relations, both based on actual experience and projection of responses to future events, and that real-life experiences are important in anticipating these emotions.

Cultural change beyond adoption dynamics: Evolutionary approaches to the discontinuation of contraception

Numerous evolutionary mechanisms have been proposed for the origins, spread and maintenance of low fertility. Such scholarship has focused on explaining the adoption of fertility-reducing behaviour, especially the use of contraceptive methods. However, this work has yet to engage fully with the dynamics of contraceptive behaviour at the individual level. Here we highlight the importance of considering not just adoption but also discontinuation for understanding contraceptive dynamics and their impact on fertility. We start by introducing contemporary evolutionary approaches to understanding fertility regulation behaviours, discussing the potential for integrating behavioural ecology and cultural evolution frameworks. Second, we draw on family planning studies to highlight the importance of contraceptive discontinuation owing to side-effects for understanding fertility rates and suggest evolutionary hypotheses for explaining patterns of variation in discontinuation rates. Third, we sketch a framework for considering how individual flexibility in contraceptive behaviour might impact the evolution of contraceptive strategies and the demographic transition. We argue that integrating public health and evolutionary approaches to reproductive behaviour might advance both fields by providing (a) a predictive framework for comparing the effectiveness of various public health strategies and (b) a more realistic picture of behaviour by considering contraceptive dynamics at the individual level more explicitly when modelling the cultural evolution of low fertility.

Psychology as a Historical Science

Psychology has traditionally seen itself as the science of universal human cognition, but it has only recently begun seriously grappling with cross-cultural variation. Here we argue that the roots of cross-cultural variation often lie in the past. Therefore, to understand not only how but also why psychology varies, we need to grapple with cross-temporal variation. The traces of past human cognition accessible through historical texts and artifacts can serve as a valuable, and almost completely unutilized, source of psychological data. These data from dead minds open up an untapped and highly diverse subject pool. We review examples of research that may be classified as historical psychology, introduce sources of historical data and methods for analyzing them, explain the critical role of theory, and discuss how psychologists can add historical depth and nuance to their work. Psychology needs to become a historical science if it wants to be a genuinely universal science of human cognition and behavior.

The multinomial index: a robust measure of reproductive skew

Inequality or skew in reproductive success (RS) is common across many animal species and is of long-standing interest to the study of social evolution. However, the measurement of inequality in RS in natural populations has been challenging because existing quantitative measures are highly sensitive to variation in group/sample size, mean RS, and age-structure. This makes comparisons across multiple groups and/or species vulnerable to statistical artefacts and hinders empirical and theoretical progress. Here, we present a new measure of reproductive skew, the multinomial index, M, that is unaffected by many of the structural biases affecting existing indices. M is analytically related to Nonacs’ binomial index, B, and comparably accounts for heterogeneity in age across individuals; in addition, M allows for the possibility of diminishing or even highly nonlinear RS returns to age. Unlike B, however, M is not biased by differences in sample/group size. To demonstrate the value of our index for cross-population comparisons, we conduct a reanalysis of male reproductive skew in 31 primate species. We show that a previously reported negative effect of group size on mating skew was an artefact of structural biases in existing skew measures, which inevitably decline with group size; this bias disappears when using M. Applying phylogenetically controlled, mixed-effects models to the same dataset, we identify key similarities and differences in the inferred within- and between-species predictors of reproductive skew across metrics. Finally, we provide an R package, SkewCalc, to estimate M from empirical data.

Why are world religions so concerned with sexual behavior?

Many religions emphasize the importance of sexual morality. This article argues mating strategies are central to understanding religion. I highlight the reproductive-religiosity model, which suggests that religious behavior is partly motivated by preferences for restricted mating strategies. I then discuss how religion can lead to reproductive benefits. Specifically, religions can make parenting a relatively safer strategy by increasing paternal certainty, which drives men toward parental investment, and alloparenting, which reduces offspring mortality rates. Next, I discuss the social implications of reproductive-religiosity, including mate selection and trust. Finally, I discuss the potential role of mating strategies in the evolution and cultural evolution of religion and discuss future directions for developing an approach to religion rooted in mating interests.

The psychology of breakup sex: Exploring the motivational factors and affective consequences of post-breakup sexual activity

Popular culture has recently publicized a seemingly new postbreakup behavior called breakup sex. While the media expresses the benefits of participating in breakup sex, there is no research to support these claimed benefits. The current research was designed to begin to better understand this postbreakup behavior. In the first study, we examined how past breakup sex experiences made the individuals feel and how people predict they would feel in the future (n = 212). Results suggested that men are more likely than women to have felt better about themselves, while women tend to state they felt better about the relationship after breakup sex. The second study (n = 585) investigated why men and women engage in breakup sex. Results revealed that most breakup sex appears to be motivated by three factors: relationship maintenance, hedonism, and ambivalence. Men tended to support hedonistic and ambivalent reasons for having breakup sex more often than women. The two studies revealed that breakup sex may be differentially motivated (and may have different psychological consequences) for men and women and may not be as beneficial as the media suggests.

Condemned and Condoned: Polygynous Marriage in Christian Africa

OBJECTIVE

This study contributes to a better understanding of the role of Christianity in the persistence of polygyny in sub-Saharan Africa.

BACKGROUND

Marital systems and practices are closely connected to religious norms, but these connections are often complex and contradictory. Polygynous marriage remains widespread in sub-Saharan Africa, including its heavily Christianized parts, where public opposition to it should be strongest.

METHODS

The study analyzes a rich combination of quantitative and qualitative data from a predominantly Christian district in Mozambique. The data include a household-based survey, a census of the district's religious congregations, and focus group discussions and individual interviews with leaders and rank-and-file members of various churches.

RESULTS

The multivariate statistical tests point to instructive denominational differences in the prevalence and acceptance of polygyny, with the starkest contrast being between two types of African Initiated Churches - one that is more lenient on pre-Christian practices and the other that is vehemently opposed to them. These tests also show a contrast between church leaders and rank-and-file members, the latter being generally more accepting of polygyny, and illustrate variations in acceptability of polygyny across different church membership scenarios. The analysis of the qualitative data complements the statistical tests by highlighting ideological and social mechanisms through which polygynous marriage is both rejected and legitimized in Christian communities.

CONCLUSION

Both condemnation and toleration of polygyny by Christian churches reflect the complexities of the transformation of sub-Saharan marital systems and of the role that religion plays in that process.

Moralizing gods, impartiality and religious parochialism across 15 societies

The emergence of large-scale cooperation during the Holocene remains a central problem in the evolutionary literature. One hypothesis points to culturally evolved beliefs in punishing, interventionist gods that facilitate the extension of cooperative behaviour toward geographically distant co-religionists. Furthermore, another hypothesis points to such mechanisms being constrained to the religious ingroup, possibly at the expense of religious outgroups. To test these hypotheses, we administered two behavioural experiments and a set of interviews to a sample of 2228 participants from 15 diverse populations. These populations included foragers, pastoralists, horticulturalists, and wage labourers, practicing Buddhism, Christianity, and Hinduism, but also forms of animism and ancestor worship. Using the Random Allocation Game (RAG) and the Dictator Game (DG) in which individuals allocated money between themselves, local and geographically distant co-religionists, and religious outgroups, we found that higher ratings of gods as monitoring and punishing predicted decreased local favouritism (RAGs) and increased resource-sharing with distant co-religionists (DGs). The effects of punishing and monitoring gods on outgroup allocations revealed between-site variability, suggesting that in the absence of intergroup hostility, moralizing gods may be implicated in cooperative behaviour toward outgroups. These results provide support for the hypothesis that beliefs in monitoring and punitive gods help expand the circle of sustainable social interaction, and open questions about the treatment of religious outgroups.

Human large-scale cooperation as a product of competition between cultural groups

A fundamental puzzle of human evolution is how we evolved to cooperate with genetically unrelated strangers in transient interactions. Group-level selection on culturally differentiated populations is one proposed explanation. We evaluate a central untested prediction of Cultural Group Selection theory, by assessing whether readiness to cooperate between individuals from different groups corresponds to the degree of cultural similarity between those groups. We documented the normative beliefs and cooperative dispositions of 759 individuals spanning nine clans nested within four pastoral ethnic groups of Kenya-the Turkana, Samburu, Rendille and Borana. We find that cooperation between groups is predicted by how culturally similar they are, suggesting that norms of cooperation in these societies have evolved under the influence of group-level selection on cultural variation. Such selection acting over human evolutionary history may explain why we cooperate readily with unrelated and unfamiliar individuals, and why humans' unprecedented cooperative flexibility is nevertheless culturally parochial.

What Makes a Partner Ideal, and for Whom? Compatibility Tests, Filter Tests, and the Mating Stability Matrix

We introduce a typological characterization of possible human heterosexual couples in terms of the concordance-opposition of the orientations of their active and receptive areas as defined by the tie-up theory. We show that human mating incentives, as characterized by widely adopted approaches, such as Becker’s marriage market approach, only capture very specific instances of actual couples thus characterized. Our approach allows us to instead explore how super-cooperation among partners vs. convenience vs. constriction may be regarded as alternatives modes of couple formation and cohesion, leading to very different types of couples with different implications in terms of stability and resilience. Our results may have interesting implications for future experimental research and for individual and family counseling.

Family Matters: Rethinking the Psychology of Human Social Motivation

What motives do people prioritize in their social lives? Historically, social psychologists, especially those adopting an evolutionary perspective, have devoted a great deal of research attention to sexual attraction and romantic-partner choice (mate seeking). Research on long-term familial bonds (mate retention and kin care) has been less thoroughly connected to relevant comparative and evolutionary work on other species, and in the case of kin care, these bonds have been less well researched. Examining varied sources of data from 27 societies around the world, we found that people generally view familial motives as primary in importance and mate-seeking motives as relatively low in importance. Compared with other groups, college students, single people, and men place relatively higher emphasis on mate seeking, but even those samples rated kin-care motives as more important. Furthermore, motives linked to long-term familial bonds are positively associated with psychological well-being, but mate-seeking motives are associated with anxiety and depression. We address theoretical and empirical reasons why there has been extensive research on mate seeking and why people prioritize goals related to long-term familial bonds over mating goals. Reallocating relatively greater research effort toward long-term familial relationships would likely yield many interesting new findings relevant to everyday people’s highest social priorities.

Evolutionary transitions toward pair living in nonhuman primates as stepping stones toward more complex societies

Nonhuman primate societies vary tremendously in size and composition, but how and why evolutionary transitions among different states occurred remains highly controversial. In particular, how many times pair living evolved and the social states of the ancestors of pair- and group-living species remains contentious. We examined evolutionary transitions in primate social evolution by using new, independent categorizations of sociality and different phylogenetic hypotheses with a vastly expanded dataset. Using Bayesian phylogenetic comparative methods, we consistently found the strongest support for a model that invokes frequent transitions between solitary ancestors and pair-living descendants, with the latter giving rise to group-living species. This result was robust to systematic variation in social classification, sample size, and phylogeny. Our analyses therefore indicate that pair living was a stepping stone in the evolution of structurally more complex primate societies, a result that bolsters the role of kin selection in social evolution.

Paid sex among men in sub-Saharan Africa: Analysis of the demographic and health survey

Background

Paying for sex is regarded as a risky sexual behavior (RSB) among heterosexual men. Men paying for sex are considered to be a bridging population for sexually transmitted infections (STIs). Despite the link between paid sex and sexual and reproductive health outcomes such as STIs, little is known about the prevalence and factors associated with paid sex among men in sub-Saharan Africa. This study examined the prevalence of paid sex and the socio-demographic factors associated with it among men in sub-Saharan Africa.

Methods

The study made use of pooled data from the Demographic and Health Surveys (DHS) conducted from January 1, 2010 to December 3, 2016 in 27 countries in sub-Saharan Africa. Binary and multivariable logistic regression models were used to investigate the relationship between the explanatory and the outcome variables.

Results

The results of the study showed that of the 139,427 men who participated in the study, 4.3% reported they had paid for sex in the 12 months preceding the survey. Men in Mozambique had the highest proportion (13.6%) of paying for sex in the 12 months preceding the survey. The results of the multivariable analysis indicated that men from DR Congo [AOR = 9.74; 95% CI = 7.45-12.73], men who had completed only primary level of education [AOR = 1.31; 95% CI = 1.18-1.45], men aged 25-34 years [AOR = 2.84; 95% CI = 2.26-3.56], men belonging to "other" religious groups [AOR = 1.20; 95% CI = 1.09-1.32] and men who were employed [AOR = 1.73; 95% CI = 1.58-1.90] had higher odds of paying for sex. Men who were divorced [AOR = 4.52; 95% = 3.89-5.25], men who read newspaper/magazine almost every day [AOR = 1.34; 95% CI = 1.12-1.63], men who listened to radio almost every day [AOR = 1.19; 95% CI = 1.05-1.36] and men who watched television at least once a week [AOR = 1.10; 95% CI = 1.01-1.19] also had higher odds of paying for sex. On the other hand, men in rural areas [AOR = 0.88; 95%CI = 0.82-0.95], men in the richest wealth quintile [AOR = 0.83; 95%CI = 0.74-0.93] and those with tertiary level of education [AOR = 0.77; 95% CI = 0.65-0.90] had lower odds of paying for sex.

Conclusion

The odds of paid sex were high among men with only primary level of education, men aged 25-34, men who professed 'other' religious affiliation, men who are employed and men who are divorced. However, paid sex was low among men in the richest wealth quintile, men with tertiary level of education and men living in rural areas. This means that the decision to pay for sex is influenced by several social and demographic factors. Hence, these factors should be taken into consideration for sexual and reproductive health interventions and services. Policy and interventional measures should aim at reducing high-risk behavior of men who pay for sex.

Comparing Relationship Quality Across Different Types of Romantic Partners in Polyamorous and Monogamous Relationships

Polyamory is the practice of having multiple emotionally close relationships that may or may not be sexual. Research concerning polyamory has just begun to determine how relationships among partners in polyamorous arrangements may vary. Most of the research assessing perceptions of polyamorous partners has focused on primary-secondary configurations; however, non-hierarchical configurations exist and can involve having multiple primary partners or having only non-primary partners. The current research is the first to examine perceptions of partners and relationship quality in various polyamorous configurations and compares results for each configuration to monogamous partners. Results from online convenience samples suggest that co-primary and non-primary configurations are common among polyamorous participants, with approximately 38% identifying with one of these configurations in 2013 and 55% in 2017. Furthermore, our results suggest that while relationships with partners in co-primary and non-primary structures still differ in some ways (e.g., investment, acceptance, secrecy, time spent having sex), they are closer to their ideals on several psychologically meaningful indicators of relationship quality (e.g., commitment and satisfaction). In other words, despite rejecting hierarchical primary-secondary labels, many of the same relationship qualities differ systematically among partners in non-hierarchical relationships. Furthermore, pseudo-primary partners and primary partners in these relationships are more comparable to monogamous partners than they are to secondary partners. We discuss how these results inform our understanding of polyamorous and monogamous relationships and suggest future directions based on these findings.

To save or not to save your family member's life? Evolutionary stability of self-sacrificing life history strategy in monogamous sexual populations

BACKGROUND

For the understanding of human nature, the evolutionary roots of human moral behaviour are a key precondition. Our question is as follows: Can the altruistic moral rule "Risk your life to save your family members, if you want them to save your life" be evolutionary stable? There are three research approaches to investigate this problem: kin selection, group selection and population genetics modelling. The present study is strictly based on the last approach.

RESULTS

We consider monogamous and exogamous families, where at an autosomal locus, dominant-recessive alleles determine the phenotypes in a sexual population. Since all individuals' survival rate is determined by their altruistic family members, we introduce a new population genetics model based on the mating table approach and adapt the verbal definition of evolutionary stability to genotypes. In general, when the resident is recessive, a homozygote is an evolutionarily stable genotype (ESG), if the number of survivors of the resident genotype of the resident homozygote family is greater than that of non-resident heterozygote survivors of the family of the resident homozygote and mutant heterozygote genotypes. Using the introduced genotype dynamics we proved that in the recessive case ESG implies local stability of the altruistic genotype. We apply our general ESG conditions for self-sacrificing life history strategy when the number of new-born offspring does not depend on interactions within the family and the interactions are additive. We find that in this case our ESG conditions give back Hamilton's rule for evolutionary stability of the self-sacrificing life history strategy.

CONCLUSIONS

In spite of the fact that the kidney transplantations was not a selection factor during the earlier human evolution, nowadays "self-sacrificing" can be observed in the live donor kidney transplantations, when the donor is one of the family members. It seems that selection for self-sacrificing in family produced an innate moral tendency in modulating social cognition in human brain.