Effects of gender inequality and wealth inequality on within-sex mating competition under hypergyny

Resources are often central to the formation and persistence of human consortships, and to the evolutionary fitness consequences of those consortships. As a result, the distribution of resources within a society should influence the number and quality of mating opportunities an individual of given status/wealth experiences. In particular, in a wide variety of societies, both contemporary and historic, women have been shown to prefer mates of higher rather than lower status and wealth, a pattern known as ‘hypergyny’. Such status-dependent within-sex competition is influenced not only by the preferences individuals express but also by the distribution of resources within and between sexes. Empirical studies show that economic inequality within a sex can amplify mating competition, and that inequalities between women and men also influence behaviours related to mating competition, but the links between resource distribution and mating competition have attracted limited systematic attention. We present simulation models of hypergynous preferences and the effects on mating competition among men and among women within a heterosexual mating market. Our modelling shows that the lower mating success of poorer men and richer women (when compared with richer men and poorer women) is worsened when resource gender gaps are relatively small or when women out-earn men on average. Likewise, high economic inequality, especially among men, amplifies the competition experienced by these groups. We consider the political implications in terms of sex- and status-dependent attitudes to gender equity, wealth inequality, and hypergynous mating norms.     

Overestimation bias in mate competition

It has been proposed that selection has shaped the human mind to be predictably biased in domains where the costs of false-positive and false-negative errors have been asymmetrical throughout human evolutionary history. Using this logic, the current study predicts that men and women systematically overestimate the degree to which members of the opposite sex find their same-sex mating competition desirable. Ten photographs of opposite-sex targets were shown to a sample of men (n=123) and women (n=159), and they were asked questions pertaining to each target's desirability as a mate. The same photographs, this time with sex of target and participant being the same, were shown to a second group of men (n=105) and women (n=103), and they were asked to estimate the desirability of the depicted individuals to members of the opposite sex. Consistent with the mate competition overestimation bias hypothesis, men and women consistently overestimated the degree to which members of the opposite sex find members of their same sex attractive and desirable as potential mates.     

Sex ratio influences the motivational salience of facial attractiveness

The sex ratio of the local population influences mating-related behaviours in many species. Recent experiments show that male-biased sex ratios increase the amount of financial resources men will invest in potential mates, suggesting that sex ratios influence allocation of mating effort in humans. To investigate this issue further, we tested for effects of cues to the sex ratio of the local population on the motivational salience of attractiveness in own-sex and opposite-sex faces. We did this using an effort-based key-press task, in which the motivational salience of facial attractiveness was assessed in samples of faces in which the ratio of male to female images was manipulated. The motivational salience of attractive opposite-sex, but not own-sex, faces was greater in the own-sex-biased (high competition for mates) than in the opposite-sex-biased (low competition for mates) condition. Moreover, this effect was not modulated by participant sex. These results present new evidence that sex ratio influences human mating-related behaviours. They also present the first evidence that the perceived sex ratio of the local population may modulate allocation of mating effort in women, as well as men.     

Environmental threat influences preferences for sexual dimorphism in male and female faces but not voices or dances

During evolution, humans faced the trade-off between preferences for feminine and masculine traits which are presumably connected to parental care, and genetic quality or provisioning abilities, respectively. Recent research has shown that environmental factors influence preferences for femininity/masculinity in potential mates. However, studies mainly focus on women's preferences for isolated cues in men. We examined the influence of pathogen and resource threat on women's and men's preference for femininity/masculinity in opposite sex unmanipulated faces, voices, and dances. Three hundred seventy (206 women) students, aged 18–35 years, from universities across the state of Sao Paulo, Brazil, were primed with newspaper-like articles on either pathogen threat (Aedes aegypti, and its mosquito-borne diseases) or resource threat (=economic crisis), and compared to a control-priming condition (lions poisoned in a Kenyan Reserve). Participants were randomly assigned to rate attractiveness of the stimuli in one of the mating strategies (i.e., short-term or long-term relationship context). After each priming article, participants rated attractiveness of pre-rated masculine and feminine stimuli of the opposite sex in a standalone-rating design. The environmental threats and the control-priming conditions were shown in a random sequence. We found that the environmental threat and the mating strategies had no systematic effect on preferences for faces, voices and behavior, suggesting that different modalities can cue to different individual qualities and can be used differently according to the environmental context and relationship strategy. The environmental threat only had a weak effect on preferences for facial femininity-masculinity: women found feminine male faces more attractive under pathogen threat, while men found feminine female faces more attractive under resource threat. This is in contrast to some previous studies, and shows that effect of ecological factors on human psychology should be submitted to a more rigorous scrutiny. The mating strategies only interacted with voice attractiveness: women rated male voices as more attractive after being primed with any type of environmental threat when considering long-term relationship context, while in men this was true when considering short-term relationship. Finally, feminine dance videos were perceived as attractive under environmental threat, irrespective of sex, type of environmental threat or mating strategy.     

Testosterone levels and their associations with lifetime number of opposite sex partners and remarriage in a large sample of American elderly men and women

Testosterone (T) has been argued to modulate mating and parenting behavior in many species, including humans. The role of T for these behaviors has been framed as the challenge hypothesis. Following this hypothesis, T should be positively associated with the number of opposite sex partners a male has. Indeed research in humans has shown that T is positively related to the number of opposite sex partners a young man has had. Here we test, in both men and women, whether this relationship extends to the lifetime number of sex partners. We also explored whether or not T was associated with current marital status, partnership status and whether or not the participant remarried. Using a large sample of elderly men and women (each sample n > 700), we show that T is positively and sizably associated with the number of opposite sex partners in men. When controlling for potential confounding variables such as educational attainment, age, BMI, ethnicity, specific use of a medication and time of sampling this effect remained. For women, the relationship between T and number of opposite sex partners was positive but did not prove to be robust. In both men and women there was no evidence for an association between T and current marital status and partnership status (being in a relationship or not). However, remarriage was positively associated with T, but only in males. Results are discussed with reference to the literature on T and sex partners, remarriage and more broadly the challenge hypothesis.     

How conception risk affects competition and cooperation with attractive women and men

We investigated competition and cooperation for resources across the menstrual cycle in the context of bargaining games. Although bargaining has been studied within an evolutionary framework, little attention has been paid specifically to the role of mating motives in economic behavior. To investigate how motives related to reproductive success affect bargaining, participants at high or low risk for conception or who were on oral contraceptives played ultimatum and dictator games with partners who varied in sex and facial attractiveness. In ultimatum games, women in the fertile phase were more competitive over resources with attractive women than with less attractive women. Intrasexual competition was not observed in dictator games. Women were more cooperative with attractive men than with less attractive men in both games, regardless of fertility status. Low fertility women were more cooperative with attractive members than with less attractive members of both sexes in both games. Results support the view that, during periods of high fertility, when women are most intrasexually competitive for mates, withholding resources from potential rivals would enable women to gain the means to enhance their attractiveness and weaken competitors' abilities to do the same at a time when relative advantages in appearance are most crucial to reproductive success. The lack of a fertility effect for cooperation with potential mates supports the view that displays of generosity accrue benefits for women across the cycle in their efforts to attract men who will invest in relationships.     

Polygamous mating system and protogynous sex change in the gobiid fish <Emphasis Type="Italic">Fusigobius neophytus</Emphasis>

Whereas mating behaviors and social structure have been studied extensively in monogamous hermaphroditic gobiid species, such studies are relatively limited for polygamous gobiid species. To investigate the reproductive strategy of polygamous gobies, mating groups of the common fusegoby Fusigobius neophytus were observed on reefs of Kuchierabu-jima Island, southern Japan. Males established mating nests on flat-rock surfaces within their territorial home ranges on sandy rubble flats. Females maintained independent home ranges outside the male home ranges during nonreproductive periods, but they shifted their home ranges to overlap with male ranges and actively visited male mating nests during their reproductive periods (1–3 days at ca. 7-day intervals). Females often changed mates during their serial mating. The mating system used by the common fusegoby fits with the definition of male-territory-visiting polygamy. The sex ratio within the study population was female-biased. Nest-holding males were significantly larger than females and were polygynous (mating with up to eight females). These characteristics fit well with the prediction of protogyny by the size-advantage model. Some of the females were observed to undergo functional sex changes to nest-holding males. In addition, small floating males demonstrated sneaking behavior. None of the floating males were derived from females that had changed sex, suggesting a diandric life-history pathway for F. neophytus.     

Sex-age stereotyping: Social perceivers as lay adaptationists

Why do perceivers categorize and stereotype others by their biological sex and age? We suggest that perceivers do so because sex and age interactively shape adaptive goals (e.g., mating, parenting) and strategies. And because such goals and strategies pose different fitness-relevant opportunities and threats, social perceivers use others' sex-age as a cue for predicting others' behaviors. This perspective has multiple implications, which we test in a range of U.S. undergraduate and online survey samples. First, we find that perceivers categorize others not by sex and age independently, but by the interaction of their sex and age (i.e., people mentally group others as females and males of specific ages) (Studies 1 and 2). Second, perceivers hold stereotypes of men and women of specific ages as being differentially oriented towards short- and long-term mating as well as parenting goals (e.g., women are stereotyped to be more oriented towards long-term mating goals than men are, but only at younger ages) (Studies 3 and 4). Finally, providing perceivers with direct information about others' adaptive goals can influence the extent to which perceivers apply stereotypes of agency, communion, and competence, and can even override typical sex stereotypes (e.g., men are generally stereotyped to be more agentic than women, but this sex stereotype disappears when both men and women are presented as engaging in short-term mating goals) (Studies 5 and 6). The current findings challenge existing thinking about sex and age stereotyping, and demonstrate the value of an adaptationist approach for thinking about social perception and stereotypes.     

Mating context and menstrual phase affect women's preferences for male voice pitch

Fundamental frequency (F₀) is the vocal acoustic parameter closest to what we perceive as pitch. Men speak at a lower F₀ than do women, even controlling for body size. Although the developmental and anatomical reasons for this sex difference are known, the evolutionary reasons are not. By examining fertility-related variation in women's preferences for men's voices, the present study tests the hypothesis that female choice for good genes influenced the evolution of male voice pitch (VP). Unlike previous correlational studies that did not consider the effects of menstrual phase and mating context on women's preferences for male VP, the present study includes these variables and utilizes experimental pitch (P) manipulations. Results indicate that low VP is preferred mainly in short-term mating contexts rather than in long-term, committed ones, and this mating context effect is greatest when women are in the fertile phase of their ovulatory cycles. Moreover, lower male F₀ correlated with higher self-reported mating success. These findings are consistent with the hypothesis that an association between low male VP and heritable fitness led to the evolution of the observed patterns in women's P preferences and men's mating success and that these patterns influenced the evolution of low VP in men. However, alternative explanations are considered.     

Seasonal Variation in Mate Choice of Photinus ignitus Fireflies

Mate choice by either sex may vary with changes in the associated costs and benefits, determined by factors such as the availability of potential mates and variation in mate quality. We examined seasonal variation in operational sex ratio, courtship behavior, spermatophore mass, egg count, and the relationship between morphological traits and mating success in Photinus ignitus fireflies to determine if mate choice in either sex varied with the availability and relative reproductive investment of fertilizable females and sexually active males. Successfully mating males had larger lanterns than unsuccessful males when the operational sex ratio was male‐biased. In addition, female responsiveness to male signals increased as the number of courting males decreased, and male spermatophore mass decreased with body size across the mating season. Successfully mating females had larger body mass than unsuccessful females. Female body mass predicted egg count and female rejection by males increased as the season progressed and female size decreased. These results suggest that both male and female P. ignitus exhibit mate choice, and that such choice is influenced by seasonal variation in the abundance and quality of potential mates.     

Evolved gender differences in mate preferences: Evidence from personal advertisements

Evolutionary theorists have posited that contemporary men and women may differ in their specific psychological mechanisms having to do with mate selection because different strategies would have benefitted men versus women in our distant ancestral past. From these theorized gender differences in mating strategies, several hypotheses were generated and subsequently tested in the current study using a large sample of personal advertisements (N = 1111). The results were generally supportive of evolutionary predictions: men were more likely than women to offer financial resources and honesty/ sincerity, and to seek attractiveness, appealing body shape, and a photograph in selecting a potential mate; women were more likely than men to offer an appealing body shape and to seek financial resources, qualities likely to lead to resource acquisition, and honesty/sincerity in potential mates. Women were also more likely than men to seek male friendship and/or companionship and to offer greater involvement only after the establishment of such friendship, whereas men more frequently than women made explicit requests for a sexual relationship. In general, men sought potential mates who were younger than themselves, a trend which became more pronounced among older advertisers. Women generally sought mates who were older than themselves, a trend which decreased slightly with the age of the advertiser. Results are discussed with regard to implications for hypothesized gender differences in evolved psychological mechanisms.     

Cues of parental investment as a factor in attractiveness

One prediction derived from parental investment theory is that women will be more attentive than men are to cues of a prospective mate's dispositions to invest in children. Research with 1793 Internet participants, representing a diverse population sample, found that (a) women tend to be generally more critical than men are in their evaluations of potential mates, but not potential friends or neighbors, and (b) cues of a positive disposition towards parental investment (DPI) have a positive influence on female evaluations of the attractiveness of males. This latter effect, however, is less domain-specific than previous research [La Cerra, M. M. (1995). Evolved mate preferences in women: Psychological adaptations for assessing a man's willingness to invest in offspring (doctoral dissertation, University of California, Santa Barbara). Dissertation Abstracts International: Section B: the Sciences & Engineering Mar, 55(9-B), 4149] indicated; it is not limited to mating contexts and to cues focusing on parental investment. In fact, much of the sex difference appears to be due to indifference by males towards cues of female DPI. A second study further clarified that the previous findings were not due solely to the Internet methodology or the immediate accessibility of images being evaluated.     

More than just a pretty face: men's priority shifts toward bodily attractiveness in short-term versus long-term mating contexts

Studies of physical attractiveness have long emphasized the constituent features that make faces and bodies attractive, such as symmetry, skin texture, and waist-to-hip ratio. Few studies, however, have examined the reproductively relevant cues conveyed by faces and bodies as whole units. Based on the premise that fertility cues are more readily assessed from a woman's body than her face, the present study tested the hypothesis that men evaluating a potential short-term mate would give higher priority to information gleaned from her body, relative to her face, than men evaluating a potential long-term mate. Male and female participants (N=375) were instructed to consider dating an opposite sex individual, whose face was occluded by a “face box” and whose body was occluded by a “body box,” as a short-term or long-term mate. With the instruction that only one box could be removed to make their decision about their willingness to engage in the designated relationship with the occluded individual, significantly more men assigned to the short-term, compared to the long-term, mating condition removed the body box. Women's face versus body information choice, in contrast, was unaffected by the temporal dimension of the mating condition. These results suggest that men, but not women, have a condition-dependent adaptive proclivity to prioritize facial cues in long-term mating contexts, but shift their priorities toward bodily cues in short-term mating contexts.     

The social biology of human populations: Spontaneous group formation conforms to evolutionary predictions of adaptive aggregation patterns

Two experiments tested whether city commuter and pedestrian groups conformed with ecological predictions of adaptive group size, age, and sex composition. It was predicted that individuals with the greatest reproductive potential would optimize mating contacts and minimize competitive interference by segregating into small, mixed-sex groups, whereas more vulnerable individuals, too young or old for optimum fertility, would tend to aggregate independently of gender in larger groups, which may offer advantages for foraging and predator avoidance. To maximize reproductive potential, mature males should prefer grouping with young women of high fertility, whereas older women should prefer younger men. In Experiment 1, 2,432 persons in three cities were observed on buses, automobiles, and sidewalks, in yoked observations. As predicted, reproductively immature preschool and grade-school children formed larger groups than mature adults (p < 0.0001) and showed no sex differences in grouping. Elderly adults (with decreased reproductive potential) were also found in larger groups than younger adults (p < 0.01) and also showed no sex differences. Sexually mature men and women grouped more with the opposite sex than in all-male or all-female groups (p < 0.00001). Mature adult men were the least aggregative category (p < 0.01): they tended to be alone or in pairs with women, and all-male groups were conspicuously absent (p < 0.005). These findings were consistent across different socioeconomic levels, ethnicities, and subcultures in our samples (p = NS). In Experiment 2, 475 bus passengers in three cities were observed selecting seatmates in a naturalistic choice paradigm. Only sexually mature adults exhibited a significant preference for the sex of their seatmates (p < 0.0005): Young women chose most often to sit with other women, whereas young adult men more frequently chose seatmates of the opposite sex. Young women were chosen more often as seat partners than all age/sex categories combined (p < 0.0005). Young women chose older partners (p < 0.05), while middle-aged women preferred younger women and men (p < 0.0005) as companions. Results are explained in the context of canalized behaviors arising early in human evolution.     

Mating strategies in two species of dart-poison frogs: a comparative study

Comparative field studies of species of dart-poison frogs in the genus Dendrobates were carried out to test predictions from two hypotheses that attempt to explain female-female competition for mates in species of Dendrobates with male parental care. The sex role reversal hypothesis proposes that males invest so much time and energy in parental care that receptive males are rare relative to receptive females, and females compete to find and mate with receptive males. The parental quality hypothesis proposes that females compete to monopolize the parental effort of particular males, because they potentially suffer a cost when their mates care for the offspring of other females. Comparisons between species with male parental care (Dendrobates leucomelas) and female parental care (Dendrobates histrionicus) contradicted prediction of the sex role reversal hypothesis, but were consistent with predictions of the parental quality hypothesis. Male D. histrionicus did not compete for mates more aggressively than male D. leucomelas, and male D. leucomelas were not more selective about mating than male D. histrionicus. Female D. leucomelas and D. histrionicus were both selective about mating; female D. leucomelas associated with and competed for particular males, whereas female D. histrionicus did not.     

Determinants of mating and sperm‐transfer success in a simultaneous hermaphrodite

The number of mating partners an individual has within a population is a crucial parameter in sex allocation theory for simultaneous hermaphrodites because it is predicted to be one of the main parameters influencing sex allocation. However, little is known about the factors that determine the number of mates in simultaneous hermaphrodites. Furthermore, in order to understand the benefits obtained by resource allocation into the male function it is important to identify the factors that predict sperm‐transfer success, i.e. the number of sperm a donor manages to store in a mate. In this study we experimentally tested how social group size (i.e. the number of all potential mates within a population) and density affect the number of mates and sperm‐transfer success in the outcrossing hermaphroditic flatworm Macrostomum lignano. In addition, we assessed whether these parameters covary with morphological traits, such as body size, testis size and genital morphology. For this we used a method, which allows tracking sperm of a labelled donor in an unlabelled mate. We found considerable variation in the number of mates and sperm‐transfer success between individuals. The number of mates increased with social group size, and was higher in worms with larger testes, but there was no effect of density. Similarly, sperm‐transfer success was affected by social group size and testis size, but in addition this parameter was influenced by genital morphology. Our study demonstrates for the first time that the social context and the morphology of sperm donors are important predictors of the number of mates and sperm‐transfer success in a simultaneous hermaphrodite. Based on these findings, we hypothesize that sex allocation influences the mating behaviour and outcome of sperm competition.     

Seeking a Sex‐Specific Coolidge Effect in a Simultaneous Hermaphrodite

In polygamous mating systems, a capability to discriminate against familiar mates may be beneficial to both sexes. Polyandrous females, for instance, may enhance the odds of finding sires with optimal genetic compatibility or high genetic quality by mating with multiple different males; polygynous males, in addition, may more efficiently invest their limited ejaculates across multiple (rather than single) females. The Coolidge effect facilitates this kind of mate discrimination, as sexual motivation declines across consecutive copulations with a familiar partner but resurrects with a novel mate. In simultaneous hermaphrodites, we expect the Coolidge effect to show sex role‐dependent patterns and vary with previous sex‐specific mating activity. Using the promiscuous hermaphroditic sea slug Chelidonura sandrana, we investigated (1) whether sexual motivation indeed declines when repeatedly exposed to familiar partners, (2) whether the Coolidge effect occurs in a sex‐specific manner and (3) whether ejaculation is strategic with respect to partner familiarity. We found neither mating latency, nor penis intromission duration, mating propensity or the frequency of sex role alternations to vary significantly with treatments. Furthermore, slugs did not donate larger ejaculates to novel than to familiar partners. Partner novelty thus elicited no detectable response in sexual motivation or mating effort in C. sandrana. We suggest that the sea slugs' promiscuous mating system in often large mating aggregations makes mate discrimination based on novelty obsolete in comparison with more relevant criteria such as partner body size or mating history.     

Effects of age and regular exercise on muscle strength and endurance

Twenty male and 20 female non-professional tennis players were classified into two different age groups (n = 10 per group): young active men (30.4 +/- 3.3 years), young active women (27.5 +/- 4.3 years), elderly active men (64.4 +/- 3.7 years), and elderly active women (65.3 +/- 4.5 years). These individuals were matched (n = 10 per group) according to sex, age, height and mass to sedentary individuals of the same socio-economical background: young sedentary men (29.2 +/- 3.4 years), young sedentary women (25.6 +/- 4.4 years), elderly sedentary men (65.2 +/- 3.2 years) and elderly sedentary women (65.6 +/- 4.4 years). An isokinetic dynamometer was used to measure the strength of the knee extensors and flexors (two separate occasions) and the endurance of the extensors. Vastus lateralis electromyogram (EMG) was measured concomitantly. Significant sex, age and exercise effects (P less than 0.001) were observed for peak torque of both muscle groups. The effect of age on extensor strength was more pronounced at high speeds where men were also able to generate larger relative torques than women. No age or sex effects were noted for muscle endurance. However, muscles of active individuals demonstrated a greater resistance to fatigue than those of sedentary individuals. In conclusion, men were found to be stronger than women, age was associated with a decrease in muscle strength, but not of muscle endurance, and tennis players were stronger and had muscles that were more resistant to fatigue than their sedentary pairs in both age groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Linking dispersal and marriage in humans: Life history data from Oakham,Massachusetts, USA (1750–1850)

Despite the emphasis on inbreeding avoidance and competition for mates in explaining primate dispersal, little is known about how dispersal and mating interconnect in humans. I examine the link between dispersal and marriage using life history data from Oakham, MA (1750–1850). I find that dispersal status, timing, and destination were linked to marital status, timing, and spouse's place of origin. Men, unmarried individuals, and individuals with spouses from Oakham were less likely to disperse than their counterparts. Individuals with spouses from Oakham also married earlier than others. For women, dispersal and marriage often coincided, and women were more likely to disperse to their spouses' town of origin than were men. Although dispersal coincided with marriage in at least two-thirds of dispersal events, the majority of cases were inconsistent with both inbreeding avoidance and mating competition explanations. Where one of these explanations was still plausible, dispersal seemed more likely linked to competition for mates than to inbreeding, with resource availability also likely shaping dispersal, and male control of resources contributing to sex biases in dispersal.