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Parental Investment and Sexual Selection

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... Beyond the role of disgust mechanisms to predict the adoption of different solutions to mate shortages, we also replicate several established effects. First, due to the greater obligatory parental investment required by women compared to men (Trivers, 1972), women likely have a greater disgust sensitivity than men do (Al-Shawaf et al., 2015;Crosby et al., 2020;Tybur et al., 2009). We seek to replicate these sex differences in disgust. ...
... We seek to replicate these sex differences in disgust. Alternatively, given the robust sex differences in mating psychology (Buss & Schmitt, 1993;Trivers, 1972), we expect to replicate sex differences in the appeal of these solutions from previous research (Jonason et al., 2020). Men should be more willing to lower their standards for short-term mates given the potential reproductive benefits ancestral men could have amassed through opportunistic matings, whereas because of the higher costs women may face for making mating mistakes, they should be more willing to abstain than men. ...
Article
When people cannot find desirable mating prospects, they may abstain, lower their standards, or travel farther to solve this mate shortage. We examined people's (N = 306) willingness to adopt these three solutions to mating shortages in relation to individual differences in disgust in men and women and for long-term and short-term partners. Those with more sexual disgust were more willing to abstain during a shortage of short-term mates and were less willing to lower their standards and to travel farther for short-term partners. Pathogen and moral disgust were associated with choosing to travel farther in the long-term contexts for men only. Our findings support the idea that how people evaluate costs and benefits in mating is expressed in their personality.
... We also find an increase in inflammatory response and a reduction in mites in autumn, which appears to be a better season for lizards generally and also probably better for production of offspring by females (Clopton and Gold 1993;Jackson and Bateman 2018;Argaez et al. 2020). Perhaps gonadal development in males is less expensive than in females and they can face that cost in a less favorable season (Trivers 1972;French and Moore 2007;Hayward and Gillooly 2011). ...
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We present the first study that compares phenological variation in parasite load and inflammatory response in a lizard with asynchronous male and female gonadal cycles. Other studies have used many species with seasonal and synchronous reproductive cycles, in which it is difficult to decouple the effects of internal and external factors that can affect parasite abundance in each sex. Species with asynchronous reproductive cycles provide the opportunity to study the effects of seasonality and reproductive condition separately, but few studies have documented variation in parasite abundance in these species. We made an extensive comparison of parasite load and inflammatory response of the lizard Sceloporus torquatus, a species with asynchronous reproductive cycles, throughout its active period. We hypothesized that the parasite load would be higher in the period of maximum gonadal activity for each sex, negatively related to body condition and inflammatory response. Our results partially support the hypothesis; males had more parasites in summer than in spring and autumn, while females had more parasites in spring and summer than in autumn; however, we do not find a relationship between parasite load, body condition and inflammatory response. Our results indicated that host-parasite interactions are complex and depend upon both environmental and internal factors. Therefore, longer-term studies may provide a more comprehensive picture of host-parasite dynamics in populations of wild lizards.
... In one chapter, Mayr (1972) tackled the important question of what exactly discriminates sexual selection from natural selection, an issue still debated today. In a book review, Williams (1973) offered the prescient observation that Trivers's (1972) chapter on parental investment and sexual selection was among "what may be the most permanently valuable part of the book" (p. 788)-in retrospect, a vast understatement. ...
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How do women's sexual interests change across their ovulatory cycles? This question is one of the most enduring within the human evolutionary behavioral sciences. Yet definitive, agreed-upon answers remain elusive. One empirical pattern appears to be robust: Women experience greater levels of sexual desire and interest when conceptive during their cycles. But this pattern is not straightforward or self-explanatory. We lay out multiple possible, broad explanations for it. Based on selectionist reasoning, we argue that the conditions that give rise to sexual interests during conceptive and non-conceptive phases are likely to differ. Because conceptive and non-conceptive sex have distinct functions, the sexual interests during conceptive and non-conceptive phases are likely to have different strategic ends. We discuss provisional evidence consistent with this perspective. But the exact nature of women's dual sexuality, if it exists, remains unclear. Additional empirical research is needed. But perhaps more crucially, this topic demands additional theory that fruitfully guides and interprets future empirical research.
... Females and males face fundamentally different biological, socio-economic, institutional, and cultural constraints (Trivers 1972;. During stochastic shocks like the Covid-19 pandemic, male and female differences may be further illuminated by historically socialised gender roles (Chan et al., 2020). ...
... An important stimulus for this belated blossoming was the publication of Sexual Selection and the Descent of Man, 1871Man, -1971, an edited volume celebrating the centenary of Darwin's opus (Campbell, 1972). This compendium included chapters by such luminaries as Loren Eiseley, George Gaylord Simpson, Theodosius Dobzhansky, and Ernst Mayr, but in a review in Science, George Williams (1973) proposed that "Parental investment and sexual selection" by the relatively unknown Robert Trivers (1972) was one of two chapters that would turn out to be "the most permanently valuable part of the book" (p. 788). ...
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Darwin’s theory of sexual selection provides a useful framework for understanding the behavior of stepparents. A non-human animal whose new mate has dependent young may kill, ignore, or adopt the predecessor’s progeny. The third option has been interpreted as courtship (“mating effort”), and whether selection favors such investment over killing or ignoring the young apparently depends on aspects of the species-typical ecology and demography. The tripartite categorization of responses is a simplification, however, There is variability both within and between species along a continuum from rejection to “full adoption.” The average stepparent invests less than the average birth parent, but more than nothing. Human stepparents have often been found to kill young children at higher rates than birth parents, but stepparental infanticide cannot plausibly be interpreted as a human adaptation, both because it is extremely rare and because it is almost certainly more likely to reduce the killer’s fitness than to raise it. How sexual selection theory remains relevant to human stepparenting is by suggesting testable hypotheses about predictors of the variability in stepparental investment.
... Previous studies focused mainly on men, investigating how they may change their behavioral manifestation to attract a potential mate (Tifferet et al., 2012;Gao et al., 2017;Bongard et al., 2019). This is probably because, due to parental investment theory (Trivers, 1972), men are supposed to be a less investing sex, and hence, less choosy about a potential partner. In this view, men must court their female partners more, performing more signaling. ...
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The signaling theory suggests that creativity may have evolved as a signal for mates. Indeed, its aesthetic value might not have been necessary for survival, but it could have helped to attract a mate, fostering childbearing. If we consider creativity as such a signal, we should expect it will be enhanced in the context related to sexual selection. This hypothesis was tested mainly for men. However, both men and women display physical and mental traits that can attract a mate. Previous studies showed that women can be more creative during their peak fertility. We advanced these findings in the present study, applying reliable measures of menstrual cycle phases (examining saliva and urine samples) and the highly recommended within-subject design. We also introduced and tested possible mediators of the effect. We found women's ideas to be more original during ovulation compared to non-fertile phases of the ovulatory cycle. The results are discussed in the context of signaling theory and alternative explanations are considered.
... In polygynous groups containing a single adult male and multiple females, the resident male is expected to invest considerable time and energy in monopolizing resident females' matings, so as to increase his reproductive success. Theoretically, males should be able to monopolize copulations when the number of resident females is small and females come into estrus at different times (Clutton-Brock, 1989;Trivers, 1972). However, this is not always the case (Isvaran & Clutton-Brock, 2007). ...
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Adult males living in a one-male multi-female social group are expected to try to monopolize copulations with resident females to increase reproductive fitness. Gibbons have traditionally been described as living in monogamous groups, with the sole resident adult male assumed to sire all of the group's offspring. Here, we used microsatellite analyses and behavioral observations to examine rates of extra-group paternity (EGP) over 16 years in a population of crested gibbons (Nomascus concolor) that form stable and long-term one-male two-female social units. Forty percent of offspring (N = 14) were sired by extra-group males. To understand this high level of EGP, we tested whether inbreeding avoidance was related to EGP. Females who engaged in EGP did not show larger pairwise relatedness with their resident male compared to females who did not engage in EGP. Nevertheless, the standardized heterozygosity of EGP offspring was significantly higher than for offspring sired by the group's resident male. These results provide partial support for the inbreeding avoidance hypothesis. It appears that resident male crested gibbons are unable to monopolize resident females' matings. Our results indicate that long-term social partners are often distinct from sexual partners in this population. Clearly, the breeding system of crested gibbons is more flexible than previously thought, indicating a need for integrating long-term behavioral data and genetic research to re-evaluate gibbon social and sexual relationships derived from concepts of monogamy and pair-bonding.
... In support of this idea, Bateman (1948) demonstrated how discriminating mate choice in females could produce greater reproductive variance in males and so encourage greater short-term mating effort. Trivers (1972) later provided an explanation for sex differences in sexual selection dynamics, which was based on variance in obligatory parental investment: the sex that devotes more resources to parental investment (typically females) is more discriminating in their mate choice and the less investing sex (typically males) devotes more energy to short-term reproductive effort and engages in more direct, risky, and potentially lethal intrasexual rivalry. Among the less investing sex, there is higher reproductive variability, the influence of sexual selection is stronger, and the development of conspicuous sexual characters is more apparent. ...
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Dominant theorizing and research surrounding the operation of intersexual selection in evolutionary psychology tends to be guided by an adaptationist framework and aligned with models of sexual selection involving direct benefits (e.g., parental care) and indirect "good gene" and condition-dependent benefits. In this way, evolutionary psychologists more often espouse Alfred Russel Wallaces' utilitarian viewpoint that traits become attractive because they honestly signal vigor and vitality, which gives priority to natural selection. In doing so, Darwin's esthetic perspective originally articulated in The Descent of Man and alternative models of sexual selection (e.g., Fisherian runaway), are given less consideration. This is despite some informative reviews on the topic in evolutionary psychology. In the current conceptual analysis, we discuss the potential of Prum's Lande-Kirkpatrick (LK) null model of sexual selection to help make sense of some of the mixed evidence regarding the links between attractive traits and purported markers of phenotypic and genetic condition. We then consider how the implications of the LK null model can help to shift theoretical assumptions and guide future work in evolutionary psychology on intersexual selection.
... In addition, maternal care in mammals may limit space use and exploration in females (Barnett & 117 McEwan, 1973;Sherry & Hampson, 1997;Trivers, 1972). With few exceptions (Costa et countered that sex differences in spatial behavior might be a byproduct of sex differences in 126 androgens rather than an adaptation based on reproductive strategies (i.e., the androgen spill-over 127 hypothesis). ...
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Sex differences in vertebrate spatial abilities are typically interpreted under the adaptive specialization hypothesis, which posits that male reproductive success is linked to larger home ranges and better navigational skills. The androgen spillover hypothesis counters that enhanced male spatial performance may be a byproduct of higher androgen levels. Animal groups that include species where females are expected to outperform males based on life-history traits are key for disentangling these hypotheses. We investigated the association between sex differences in reproductive strategies, spatial behavior, and androgen levels in three species of poison frogs. We tracked individuals in natural environments to show that contrasting parental sex roles shape sex differences in space use, where the sex performing parental duties shows wider-ranging movements. We then translocated frogs from their home areas to test their navigational performance and found that the caring sex outperformed the non-caring sex only in one out of three species. In addition, males across species displayed more explorative behavior than females. Furthermore, androgen levels correlated with explorative behavior and homing accuracy. Our findings suggest that poison frog reproductive strategies shape space use patterns but not navigational performance, providing counterevidence to the prevailing view of adaptive sex differences in spatial abilities.
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Background Early women's marriage is associated with adverse outcomes for mothers and their offspring, including reduced human capital and increased child undernutrition and mortality. Despite preventive efforts, it remains common in many populations and is often favored by cultural norms. A key question is why it remains common, given such penalties. Using an evolutionary perspective, a simple mathematical model was developed to explore women's optimal marriage age under different circumstances, if the sole aim were to maximize maternal or paternal lifetime reproductive fitness (surviving offspring).Methods The model was based on several assumptions, supported by empirical evidence, regarding relationships between women's marital age and parental and offspring outcomes. It assumes that later marriage promotes women's autonomy, enhancing control over fertility and childcare, but increases paternity uncertainty. Given these assumptions, optimal marriage ages for maximizing maternal and paternal fitness were calculated. The basic model was then used to simulate environmental changes or public health interventions, including shifts in child mortality, suppression of women's autonomy, or promoting women's contraception or education.ResultsIn the basic model, paternal fitness is maximized at lower women's marriage age than is maternal fitness, with the paternal optimum worsening child undernutrition and mortality. A family planning intervention delays marriage age and reduces child mortality and undernutrition, at a cost to paternal but not maternal fitness. Reductions in child mortality favor earlier marriage but increase child undernutrition, whereas ecological shocks that increase child mortality favor later marriage but reduce fitness of both parents. An education intervention favors later marriage and reduces child mortality and undernutrition, but at a cost to paternal fitness. Efforts to suppress maternal autonomy substantially increase fitness of both parents, but only if other members of the household provide compensatory childcare.Conclusion Early women's marriage maximizes paternal fitness despite relatively high child mortality and undernutrition, by increasing fertility and reducing paternity uncertainty. This tension between the sexes over the optimal marriage age is sensitive to ecological stresses or interventions. Education interventions seem most likely to improve maternal and child outcomes, but may be resisted by males and their kin as they may reduce paternal fitness.
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