Shared interests or sexual conflict? Spousal age gap,women's wellbeing and fertility in rural Tanzania

The marriage of older men to younger women is common across cultures. On one hand, husband-older marriage may serve the interests of both sexes, a conclusion broadly consistent with reported gender differences in mate preferences. On the other hand, men alone may benefit from such marriages at a cost to women if seniority enables men to exert dominance in conflicts of interest. Indeed, in public health large spousal age gaps are generally deemed “pathological”, both as a cause and consequence of gender inequalities harmful to women. We investigate these alternative models of spousal age gap using data from a cross-sectional survey of women in Mwanza, northwestern Tanzania (n = 993). Consistent with the notion that spousal age gaps are a product of sexual conflict, women typically married with a larger age gap than stated ideals. However, adjusting for potential confounds, spousal age gap was not associated with fertility or the risk of divorce. Furthermore, women's mental health and autonomy in household decision-making was higher in husband-older marriages compared to rare cases of same-age or wife-older marriage. Beyond this comparison, the magnitude of spousal age gaps was unrelated to either measure of women's wellbeing among the overwhelming majority of marriages where the husband was older. Together these findings suggest husband-older marriage does not influence marital stability, relatively large spousal age gaps are neither especially costly nor beneficial to women, and that alternative sociodemographic factors are more important in driving variation in women's wellbeing and reproductive success in this context. Our results support neither a model of mutual benefits, nor a pathological conceptualization of spousal age gaps. We conclude by both encouraging evolutionary human scientists to engage more fully with models of sexual conflict in future studies of marriage and mating, and suggesting that public health scholars consider more neutral interpretations of spousal age differences.     

What do men want? Re-examining whether men benefit from higher fertility than is optimal for women

Several empirical observations suggest that when women have more autonomy over their reproductive decisions, fertility is lower. Some evolutionary theorists have interpreted this as evidence for sexual conflicts of interest, arguing that higher fertility is more adaptive for men than women. We suggest the assumptions underlying these arguments are problematic: assuming that women suffer higher costs of reproduction than men neglects the (different) costs of reproduction for men; the assumption that men can repartner is often false. We use simple models to illustrate that (i) men or women can prefer longer interbirth intervals (IBIs), (ii) if men can only partner with wives sequentially they may favour shorter IBIs than women, but such a strategy would only be optimal for a few men who can repartner. This suggests that an evolved universal male preference for higher fertility than women prefer is implausible and is unlikely to fully account for the empirical data. This further implies that if women have more reproductive autonomy, populations should grow, not decline. More precise theoretical explanations with clearly stated assumptions, and data that better address both ultimate fitness consequences and proximate psychological motivations, are needed to understand under which conditions sexual conflict over reproductive timing should arise.     

Evidence supporting nubility and reproductive value as the key to human female physical attractiveness

Selection should favor mating preferences that increase the chooser's reproductive success. Many previous studies have shown that the women men find most attractive in well-nourished populations have low body mass indices (BMIs) and small waist sizes combined with relatively large hips, resulting in low waist-hip ratios (WHRs). A frequently proposed explanation for these preferences is that such women may have enhanced health and fertility; but extensive evidence contradicts this health-and-fertility explanation. An alternative view is that men are attracted to signs of nubility and high reproductive value, i.e., by indicators of physical and sexual maturity in young women who have not been pregnant. Here we provide evidence in support of the view that a small waist size together with a low WHR and BMI is a strong and reliable sign of nubility. Using U.S. data from large national health surveys, we show that WHR, waist/thigh, waist/stature, and BMI are all lower in the age group (15-19) in which women reach physical and sexual maturity, after which all of these anthropometric measures increase. We also show that a smaller waist, in conjunction with relatively larger hips or thighs, is strongly associated with nulligravidity and with higher blood levels of docosahexaenoic acid (DHA), a fatty acid that is probably limiting for infant brain development. Thus, a woman with the small waist and relatively large hips that men find attractive is very likely to be nubile and nulliparous, with maximal bodily stores of key reproductive resources.     

Fertility and race perception predict voter preference for Barack Obama

Research shows that women more positively evaluate targets evincing cues of high male genetic quality as a function of fertility across the menstrual cycle. Recently, a link between fertility and anti-black race bias has also been documented, an effect that is argued to serve a sexual coercion avoidance function. Here we demonstrate that both effects can be operative toward the same male target depending on inter-individual differences in race perception of the target. Across two studies, we found that the intention to vote for Barack Obama in the months preceding the 2008 election increased as a function of conception risk across the menstrual cycle. In the second study, we found that the effect is greatest among women who perceived him as more white than black, whereas the opposite was true among women who perceived him as mostly black. Our findings tie together separate conceptual research threads on positive and negative evaluations of men by women across the menstrual cycle — integrating them to shed light on women's voting preferences.     

Women's attractiveness is linked to expected age at menopause

A great number of studies have shown that features linked to immediate fertility explain a large part of the variance in female attractiveness. This is consistent with an evolutionary perspective, as men are expected to prefer females at the age at which fertility peaks (at least for short‐term relationships) in order to increase their reproductive success. However, for long‐term relationships, a high residual reproductive value (the expected future reproductive output, linked to age at menopause) becomes relevant as well. In that case, young age and late menopause are expected to be preferred by men. However, the extent to which facial features provide cues to the likely age at menopause has never been investigated so far. Here, we show that expected age at menopause is linked to facial attractiveness of young women. As age at menopause is heritable, we used the mother's age at menopause as a proxy for her daughter's expected age of menopause. We found that men judged faces of women with a later expected age at menopause as more attractive than those of women with an earlier expected age at menopause. This result holds when age, cues of immediate fertility and facial ageing were controlled for. Additionally, we found that the expected age at menopause was not correlated with any of the other variables considered (including immediate fertility cues and facial ageing). Our results show the existence of a new correlate of women's facial attractiveness, expected age at menopause, which is independent of immediate fertility cues and facial ageing.     

Women's autonomy and reproductive preferences in Eritrea

Current research and policies on reproductive behaviours in many East African countries focus primarily on proxy indicators of women's autonomy, and very little emphasis is placed on direct indicators of women's autonomy. In this paper, data from the 2002 Eritrea Demographic and Health Survey (EDHS) are used to address some of the most frequently raised questions about the link between women's autonomy and reproductive behaviour. The results from the multivariate logistic models show that although the relationship between women's autonomy and reproductive preferences in Eritrea is complex, some clear, broad patterns exist that have implications for theory and policy. First, although the different dimensions of women's autonomy influence the outcome variables differently in terms of magnitude and statistical significance, most of them have a strong connection; in particular, women's final say in decisions regarding day-to-day household purchases and spousal communication are significant explanatory variables in fertility preferences and ever-use of modern contraception. Second, many background (proxy) variables, particularly household economic condition and employment, exert a strong and independent influence over fertility preferences and ever-use of contraception regardless of a woman's autonomy. In their relationship to reproductive behaviours, therefore, employment and economic status cannot be considered as proxies for women's autonomy in Eritrea. A complete explanation of the relationship between women's autonomy and reproductive preferences must recognize the effects of both the background and direct autonomy indicators. Interventions are needed to improve women's decision-making autonomy and strengthen their negotiating capacity on family planning if an increased desire to limit fertility is to be attained.     

Sexual selection and speciation in mammals,butterflies and spiders

Recently refined evolutionary theories propose that sexual selection and reproductive conflict could be drivers of speciation. Male and female reproductive optima invariably differ because the potential reproductive rate of males almost always exceeds that of females: females are selected to maximize mate 'quality', while males can increase fitness through mate 'quantity'. A dynamic, sexually selected conflict therefore exists in which 'competitive' males are selected to override the preference tactics evolved by 'choosy' females. The wide variation across taxa in mating systems therefore generates variance in the outcome of intrasexual conflict and the strength of sexual selection: monandry constrains reproductive heterozygosity and allows female choice to select and maintain particular (preferred) genes; polyandry promotes reproductive heterozygosity and will more likely override female choice. Two different theories predict how sexual selection might influence speciation. Traditional ideas indicate that increased sexual selection (and hence conflict) generates a greater diversity of male reproductive strategies to be counteracted by female mate preferences, thus providing elevated potentials for speciation as more evolutionary avenues of male-female interaction are created. A less intuitively obvious theory proposes that increased sexual selection and conflict constrains speciation by reducing the opportunities for female mate choice under polyandry. We use a comparative approach to test these theories by investigating whether two general measures of sexual selection and the potential for sexual conflict have influenced speciation. Sexual size dimorphism (across 480 mammalian genera, 105 butterfly genera and 148 spider genera) and degree of polyandry (measured as relative testes size in mammals (72 genera) and mating frequency in female butterflies (54 genera)) showed no associations with the variance in speciosity. Our results therefore show that speciation occurs independently of sexual selection.     

Blood,solidarity, status,and honor: The sexual balance of power and spousal abuse in Sonora,Mexico

Independent samples of 128 women and 106 men were interviewed in a study site in Hermosillo, Sonora, Mexico. Respondents were screened for involvement in a committed sexual relationship during the past year, but not with each other. Questions pertained to family structure, support, and conflict; females reported on victimization by spousal aggression and males on perpetration. Previously documented effects of their partner's mate quality (“sex”) and socioeconomic status (“money”) were cross-culturally replicated. The following family structure parameters were also measured: (1) the local density of female kin, (2) the local density of male kin, (3) the social support provided by local kin, (4) the socioeconomic status of close kin, and (5) the “culture of honor” revenge ideology of the respondents. The same interactions of local density of male kin that protected women from spousal abuse also empowered men to perpetrate it. The risk of spousal abuse was mitigated by the “sexual balance of power” between the family structures of potential victims and potential perpetrators. Evidence was also found partially supporting several alternative hypotheses tested regarding local cultural and ideological mechanisms (culture of honor and patriarchal beliefs), major dimensions of psychopathology (anxiety and depression) and substance abuse (alcohol), and indicators of general criminality (permissive and risk-taking attitudes).     

Cross-cultural dimensions of breastfeeding practices and abstinence: Evidence from Uttar Pradesh and Tamilnadu, India

Summary and Conclusion The analysis contained in this paper brings out very clearly that the practice of breastfeeding and abstinence in the two major states of India: Uttar Pradesh and Tamilnadu are highly related to socio-cultural factors and changes in generational gaps. The findings reveal that literate, non-Hindu, and rich (high SLI) women have shorter breastfeeding durations than illiterates, Hindus, and poor (low SLI) women of Uttar Pradesh and Tamilnadu. In addition, the breastfeeding practice in Uttar Pradesh is influenced by residence background and generational age-gaps. The role of socio-cultural factors in influencing post-partum sexual abstinence period has been found to be significantly important through the variables; residence background, generational age-gaps, religion and working status of women. The results reveal that urban women, of younger cohorts (below 30 years), non-Hindu, and non-working women have shorter abstinence periods compared to rural women, of older cohorts (above 30 years), Hindus, and working women in both the states. The findings from this analysis suggest that apart from modernization process, defined in terms of higher literacy levels, higher developmental and urbanization levels, the changing perceptions and attitude towards lactational practices over the generation has significant dent on shortening of breastfeeding durations and abstinence periods. Thus, the study support the hypothesis that the process of modernization defined in terms of improvement in level of education, family income, urbanization tends to shorten the period of breastfeeding and abstinence, and consequently, the post-partum infecundability is reduced. Such reductions in the infertile periods can be expected to contribute to an increase in natural fertility levels of the population and also on the observed fertility levels, if not counter balanced by the fertility reducing effects of contraception.     

Does Sexual Conflict between Mother and Father Lead to Fertility Decline?

Fertility decline is a great challenge to evolutionary approaches to human behavior. In this study, we apply the perspective of sexual conflict between mother and father to the fertility decline. We predict that, under serial monogamy allowing for mate changes, the ideal number of children for women should be smaller than that for men, because the cost of reproduction for women should be higher than that for men. Our reasoning is that if the cost of child-bearing and child-rearing is higher for women than men, and if women, who therefore would want a smaller number of children than their husbands, have gained more power in reproductive decision-making within a couple owing to the modernization of society, fertility should decline. Until now, few evolutionary studies have analyzed empirical data in modern developed societies with such a perspective. Our questionnaire survey in an urban area in Japan revealed that mothers did experience greater cost during childcare than fathers. However, in contrast to our prediction, we found no sex differences in the ideal number of children between mothers and their husbands in many cases. About 60% of parents remembered wanting two children when they were childless. Moreover, mothers and their husbands had equal power in their decision-making regarding having children. After presenting these results, we discuss some perspectives to advance our understanding of fertility decline in terms of sexual conflict.     

Sex and age differences in preferences and tactics of mate attraction: Analysis of published advertisements

Using the theoretical perspective of evolutionary biology, 13 hypotheses were generated concerning sex and age differences in human mate preferences and tactics of mate attraction. Classified “lonely hearts” advertisements (N = 1,000) from a nationally circulated, fortnightly magazine were content-analyzed. Men, more than women, sought cues to reproductive value (i.e., physical appearance and youth), whereas women, more than men, sought cues revealing an ability to acquire resources (i.e., actual and potential financial security and older men). Women also sought to ascertain a man's willingness to provide resources (in the form of time, emotions, money, and status) in a relationship. Both sexes offered those traits sought by the opposite sex. Men were more promiscuously inclined than women, favoring casual relationships and being more likely to be married, whereas women sought long-term monogamous relationships. These differences support evolutionary predictions based on concepts of sexual selection, parental investment, and reproductive capacities and confirm the use of personal advertisements as a valuable method of research.     

Does attractiveness in men provide clues to semen quality?

The psychological mechanisms underlying attractiveness judgements in humans are thought to be evolved adaptations for finding a high quality mate. The phenotype-linked fertility hypothesis proposes that females obtain reliable information on male fertility from male expression of sexual traits. A previous study of Spanish men reported that facial attractiveness was positively associated with semen quality. We aimed to determine whether this effect was widespread by examining a large sample of Australian men. We also extended our study to determine whether cues to semen quality are provided by components of attractiveness: masculinity, averageness and symmetry. Each male participant was photographed and provided a semen sample that was analyzed for sperm morphology, motility and concentration. Two independent sets of women rated the male photographs for attractiveness, and three further sets of 12 women rated the photographs for masculinity, symmetry or averageness. We found no significant correlations between semen quality parameters and attractiveness or attractive traits. Although male physical attractiveness may signal aspects of mate quality, our results suggest that phenotype-linked cues to male fertility may not be general across human populations.     

Divergent selection on,but no genetic conflict over,female and male timing and rate of reproduction in a human population

The sexes often have different phenotypic optima for important life-history traits, and because of a largely shared genome this can lead to a conflict over trait expression. In mammals, the obligate costs of reproduction are higher for females, making reproductive timing and rate especially liable to conflict between the sexes. While studies from wild vertebrates support such sexual conflict, it remains unexplored in humans. We used a pedigreed human population from preindustrial Finland to estimate sexual conflict over age at first and last reproduction, reproductive lifespan and reproductive rate. We found that the phenotypic selection gradients differed between the sexes. We next established significant heritabilities in both sexes for all traits. All traits, except reproductive rate, showed strongly positive intersexual genetic correlations and were strongly genetically correlated with fitness in both sexes. Moreover, the genetic correlations with fitness were almost identical in men and women. For reproductive rate, the intersexual correlation and the correlation with fitness were weaker but again similar between the sexes. Thus, in this population, an apparent sexual conflict at the phenotypic level did not reflect an underlying genetic conflict over the studied reproductive traits. These findings emphasize the need for incorporating genetic perspectives into studies of human life-history evolution.     

Cues to fertility: perceived attractiveness and facial shape predict reproductive success

Attractive facial features in women are assumed to signal fertility, but whether facial attractiveness predicts reproductive success in women is still a matter of debate. We investigated the association between facial attractiveness at young adulthood and reproductive life history—number of children and pregnancies—in women of a rural community. For the analysis of reproductive success, we divided the sample into women who used contraceptives and women who did not. Introducing two-dimensional geometric morphometric methodology, we analysed which specific characteristics in facial shape drive the assessment of attractiveness and covary with lifetime reproductive success. A set of 93 (semi)landmarks was digitized as two-dimensional coordinates in postmenopausal faces. We calculated the degree of fluctuating asymmetry and regressed facial shape on facial attractiveness at youth and reproductive success. Among women who never used hormonal contraceptives, we found attractive women to have more biological offspring than less attractive women. These findings are not affected by sociodemographic variables. Postmenopausal faces corresponding to high reproductive success show more feminine features—facial characteristics previously assumed to be honest cues to fertility. Our findings support the notion that facial attractiveness at the age of mate choice predicts reproductive success and that facial attractiveness is based on facial characteristics, which seem to remain stable until postmenopausal age.     

Reproduction in high altitude Aymara: physiological stress and fertility planning?

Reproductive characteristics at high altitude are described based on the reproductive histories of 720 Aymara women, collected in 1998 and 1999 in a group of twelve peasant communities at a mean altitude of 4000 m in the Bolivian Altiplano. The reproductive pattern is shaped by a late onset of childbearing, associated with a rather short reproductive span and large birth intervals. Environmental conditions could explain the particularly late age at menarche of rural girls compared with their urban counterparts, whereas the age at first birth is likely to be under cultural control. The short reproductive span appears to result from a large mean interval between last birth and menopause, which is essentially determined by cultural decisions. The birth intervals, which are longer than in many traditional societies, could be the result of a slower restoration of postpartum fecundability induced by the hard way of life inherent in the Altiplano (including poor sanitary and nutritional conditions and high workload), perhaps aggravated by hypoxia. However, a secular trend in fertility is perceptible, towards earlier menarche, earlier age at first birth, increasing reproductive span and a slight increase in live births and surviving offspring, which is probably the result of a slow improvement in living conditions. The existence of birth control on the one hand, and a total fertility rate averaging six live births among the couples who do not practise contraception on the other, are other arguments against the hypothesis of a low natural fecundity in these Aymara groups.     

Are Individual and Community Acceptance and Witnessing of Intimate Partner Violence Related to Its Occurrence? Multilevel Structural Equation Model

Background

Intimate partner violence against women (IPVAW) is a serious and widespread problem worldwide. Much of the research on IPVAW focused on individual-level factors and attention has been paid to the contextual factors. The aim of this study was to develop and test a model of individual- and community-level factors associated with IPVAW.

Methods and Findings

We conducted a (multivariate) multilevel structural equation analysis on 8731 couples nested within 883 communities in Nigerian Demographic and Health Survey 2008. Variables included in the model were derived from respondents'' answers to the experience of IPVAW, attitudes towards wife beating and witnessing physical violence in childhood. We found that women that witnessed physical violence were more likely to have tolerant attitudes towards IPVAW and women with tolerant attitudes were more likely to have reported spousal IPVAW abuse. Women with husbands with tolerant attitudes towards IPVAW were more likely to have reported spousal abuse. We found that an increasing proportion of women in the community with tolerant attitudes was significantly positively associated with spousal sexual and emotional abuse, but not significantly associated with spousal physical abuse. In addition, we found that an increasing proportion of men in the community with tolerant attitudes and an increasing proportion of women who had witnessed physical violence in the community was significantly positively associated with spousal physical abuse, but not significantly associated with spousal sexual and emotional abuse. There was a positive correlation between all three types of IPVAW at individual- and community-level.

Conclusions

We found that community tolerant attitudes context in which people live is associated with exposure to IPVAW even after taking into account individual tolerant attitudes. Public health interventions designed to reduce IPVAW must address people and the communities in which they live in order to be successful.     

Women's height,reproductive success and the evolution of sexual dimorphism in modern humans

Recent studies have shown that, in contemporary populations, tall men have greater reproductive success than shorter men. This appears to be due to their greater ability to attract mates. To our knowledge, no comparable results have yet been reported for women. This study used data from Britain's National Child Development Study to examine the life histories of a nationally representative group of women. Height was weakly but significantly related to reproductive success. The relationship was U-shaped, with deficits at the extremes of height. This pattern was largely due to poor health among extremely tall and extremely short women. However, the maximum reproductive success was found below the mean height for women. Thus, selection appears to be sexually disruptive in this population, favouring tall men and short women. Over evolutionary time, such a situation tends to maintain sexual dimorphism. Men do not use stature as a positive mate-choice criterion as women do. It is argued that there is good evolutionary reason for this, because men are orientated towards cues of fertility, and female height, being positively related to age of sexual maturity, is not such a cue.     

Women’s faces and voices are cues to reproductive potential in industrial and forager societies

Women’s faces and voices may be cues to their reproductive potential. If so, then individual differences in indices of female fecundity and residual reproductive value, such as hormonal profiles, body composition, and age, should be associated with women’s facial and vocal attractiveness to men. However, previous research on these associations is sparse, has rendered mixed results, and is limited to Western samples. The current study therefore explored relationships between correlates of reproductive capability (testosterone levels, age, and body mass index [BMI]) and facial and vocal attractiveness in women from industrial and foraging societies. Women’s facial and vocal attractiveness was associated with each of these indicators in at least one of the two samples. The patterns of these associations suggest that women’s faces and voices provide cues to both common and unique components of reproductive potential and help explain the evolution of men’s mating preferences.     

Evidence of adaptation for mate choice within women's memory

Sexually dimorphic characteristics in men may act as cues, advertising long-term health, dominance, and reproductive potential to prospective mates. Evolution has accordingly adapted human cognition so that women perceive sexually dimorphic facial features as important when judging the attractiveness and suitability of potential mates. Here we provide evidence showing, for the first time, that women's memory for details encountered in recently experienced episodes is also systematically biased by the presence of men's facial cues signaling enhanced or reduced sexual dimorphism. Importantly, the direction and strength of this bias are predicted by individual differences in women's preferences for masculine versus feminine facial features in men and are triggered specifically while viewing images of male but not female faces. No analogous effects were observed in male participants viewing images of feminized and masculinized women's faces despite the fact that male participants showed strong preferences for feminized facial features. These findings reveal a preference-dependent memory enhancement in women that would promote retention of information from encounters with preferred potential mates. We propose that women's memory for recently experienced episodes may therefore be functionally specialized for mate choice and in particular for the comparative evaluation of alternative potential mates. This also raises the possibility that similar specialization may be present in other species where it has been established that precursor, ‘episodic-like’ forms of memory exist.     

Sensation seeking and men's face preferences

Findings from previous studies suggest that only men who are in good physical condition can afford to pursue high-risk activities and that men who engage in high-risk activities are considered particularly attractive by women. Here, we show that men's interest in high-sensation activities, a personality trait that is known to increase the likelihood of those individuals engaging in high-risk behaviors, is positively related to the strength of their preferences for femininity in women's faces (Studies 1–3) but is not related to the strength of their preferences for femininity in men's faces (Study 2). We discuss these findings as evidence for potentially adaptive condition-dependent mate preferences, whereby men who exhibit signals of high quality demonstrate particularly strong preferences for facial cues of reproductive and medical health in potential mates because they are more likely than lower-quality men to succeed in acquiring such partners.