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Income inequality generates and amplifies incentives, particularly incentives for individuals to elevate or maintain their status, with important consequences for the individuals involved and aggregate outcomes for their societies [R. G. Wilkinson, K. E. Pickett, Annu. Rev. Sociol. 35, 493–511 (2009)]. Economically unequal environments intensify men’s competition for status, respect, and, ultimately, mating opportunities, thus elevating aggregate rates of violent crime and homicide [M. Daly, M. Wilson, Evolutionary Psychology and Motivation (2001)]. Recent evidence shows that women are more likely to post “sexy selfies” on social media and that they spend more on beautification in places where inequality is high rather than low [K. R. Blake, B. Bastian, T. F. Denson, et al., Proc. Natl. Acad. Sci. U.S.A. 115, 8722–8727 (2018)]. Here we test experimentally for causal links between income inequality and individual self-sexualization and status-related competition. We show that manipulating income inequality in a role-playing task indirectly increases women’s intentions to wear revealing clothing and that it does so by increasing women’s anxiety about their place in the social hierarchy. The effects are not better accounted for by wealth/poverty than by inequality or by modeling anxiety about same-sex competitors in place of status anxiety. The results indicate that women’s appearance enhancement is partly driven by status-related goals.

Because sexual attraction is a key driver of human mate choice and reproduction, we descriptively assess relative sex differences in the level of attraction individuals expect in the aesthetic, resource, and personality characteristics of potential mates. As a novelty we explore how male and female sexual attractiveness preference changes across age, using a dataset comprising online survey data for over 7,000 respondents across a broad age distribution of individuals between 18 and 65 years. In general, we find that both males and females show similar distribution patterns in their preference responses, with statistically significant sex differences within most of the traits. On average, females rate age, education, intelligence, income, trust, and emotional connection around 9 to 14 points higher than males on our 0–100 scale range. Our relative importance analysis shows greater male priority for attractiveness and physical build , compared to females, relative to all other traits. Using multiple regression analysis, we find a consistent statistical sex difference (males relative to females) that decreases linearly with age for aesthetics , while the opposite is true for resources and personality , with females exhibiting a stronger relative preference, particularly in the younger aged cohort. Exploring non-linearity in sex difference with contour plots for intelligence and attractiveness across age (mediated by age) indicates that sex differences in attractiveness preferences are driven by the male cohort (particularly age 30 to 40) for those who care about the importance of age, while intelligence is driven by females caring relatively more about intelligence for those who see age as very important (age cohort 40 to 55). Overall, many of our results indicate distinct variations within sex at key life stages, which is consistent with theories of selection pressure. Moreover, results also align with theories of parental investment, the gender similarities hypothesis, and mutual mate choice–which speaks to the fact that the broader discipline of evolutionary mate choice research in humans still contains considerable scope for further inquiry towards a unified theory, particularly when exploring sex-difference across age.

The links between fitness, health, sexual signals and mate choice are complex and subject to ongoing study. In 1999, von Schantz et al. made the valuable suggestion that oxidative stress may be an important missing piece of this complex puzzle. Their suggestion has been enthusiastically tested, with over 300 studies citing their paper, but most effort has concerned carotenoid-based (and to a lesser extent melanin-based) visual signals, predominantly in birds and fishes. Today, we know a great deal more about oxidative stress and related physiology, in both a pathological and regulatory sense, than we did in 1999. We revisit von Schantz et al.'s predictions and, more importantly, highlight novel mechanisms that could link oxidative stress with a range of energetically demanding signals, greatly increasing the scope from visual signalling systems that are usually discussed and nearly always tested. In particular, we argue that differences between individuals in their ability to regulate physiology related to oxidative stress may be an important factor influencing the production of sexual signals and the costs that are incurred from investment.

Trade-offs between growth, reproduction, and lifespan constrain animal life histories, leading to evolutionary diversification of life history cycles in different environments. In female mammals, gestation and lactation are expected to impose the major costs of reproduction, driving reproductive trade-offs, although mating also requires interactions with males that could themselves influence life history. Here we show that a male’s presence by itself leads to lifelong alterations in life history in female mice. Housing C57BL/6J female mice with sterilized males early in life led to an increase in body weight, an effect that persisted across life even when females were later allowed to produce pups. We found that those females previously housed with sterile males also showed enhanced late-life offspring production when allowed to reproduce, indicating that earlier mating can influence subsequent fecundity. This effect was the opposite to that seen in females previously housed with intact males, which showed the expected trade-off between early-life and late-life reproduction. However, housing with a sterile male early in life came at a cost to lifespan, which was observed in the absence of females ever undergoing fertilization. Endocrinologically, mating also permanently reduced the concentration of circulating prolactin, a pituitary hormone influencing maternal care. Changes in hormone axes that influence reproduction could therefore help alter life history allocation in response to opposite-sex stimuli. Our results demonstrate that mating itself can increase growth and subsequent fecundity in mammals, and that responses to sexual stimuli could account for some lifespan trade-offs normally attributed to pregnancy and lactation.

Biomedical and clinical sciences are experiencing a renewed interest in the fact that males and females differ in many anatomic, physiological, and behavioural traits. Sex differences in trait variability, however, are yet to receive similar recognition. In medical science, mammalian females are assumed to have higher trait variability due to estrous cycles (the ‘estrus-mediated variability hypothesis’); historically in biomedical research, females have been excluded for this reason. Contrastingly, evolutionary theory and associated data support the ‘greater male variability hypothesis’. Here, we test these competing hypotheses in 218 traits measured in >26,900 mice, using meta-analysis methods. Neither hypothesis could universally explain patterns in trait variability. Sex bias in variability was trait-dependent. While greater male variability was found in morphological traits, females were much more variable in immunological traits. Sex-specific variability has eco-evolutionary ramifications, including sex-dependent responses to climate change, as well as statistical implications including power analysis considering sex difference in variance. Males and females differ in appearance, physiology and behavior. But we do not fully understand the health and evolutionary consequences of these differences. One reason for this is that, until recently, females were often excluded from medical studies. This made it difficult to know if a treatment would perform as well in females as males. To correct this, organizations that fund research now require scientists to include both sexes in studies. This has led to some questions about how to account for sex differences in studies. One reason females have historically been excluded from medical studies is that some scientists assumed that they would have more variable responses to a particular treatment based on their estrous cycles. Other scientists, however, believe that males of a given species might be more variable because of the evolutionary pressures they face in competing for mates. Better understanding how males and females vary would help scientists better design studies to ensure they provide accurate answers. Now, Zajitschek et al. debunk both the idea that males are more variable and the idea that females are more variable. To do this, Zajitschek et al. analyzed differences in 218 traits, like body size or certain behaviors, among nearly 27,000 male and female mice. This showed that neither male mice nor female mice were universally more different from other mice of their sex across all features. Instead, sex differences in how much variation existed in male or female mice depended on the individual trait. For example, males varied more in physical features like size, while females showed more differences in their immune systems. The results suggest it is particularly important to consider sex-specific variability in both medical and other types of studies. To help other researchers better design experiments to factor in such variability, Zajitschek et al. created an interactive tool that will allow scientists to look at sex-based differences in individual features among male or female mice.

Previous research finds that both men and women perceive sexualized women as lacking in certain human qualities such as mental capacity and moral status. The mechanism underlying this effect, however, is unclear. The present two studies test how appearance-based judgements affect the degree to which a broad sample of women are objectified. In Study 1 (N = 279), full-body images of women wearing different clothing outfits were rated by male and female participants on perceived attractiveness, sexual intent and age. In Study 2, male and female participants (N = 1,695) viewed these same images from Study 1 and rated them on two dimensions of objectification (agency and patiency). We analyzed associations between these dimensions of objectification and the averaged appearance-based perceptions from Study 1. We find that women perceived as more open to casual sex are attributed less mental capacity and less moral status. We also find that participants tend to associate attractiveness with greater mental and moral status in women, but we find only limited evidence that perceived age influences objectification. Our findings suggest that although positive attractiveness biases may mitigate the amount a woman is objectified, greater female objectification may be prompted by observers' negative stereotypes of promiscuous women.

Selection has led to the evolution of a variety of different mating strategies, each adapted to different competitive challenges. But what happens if the competitive challenges depend on the social environment? Here we discuss and review examples of socially cued anticipatory plasticity: irreversible developmental tactics in which resource allocation during the juvenile stage is altered to develop an appropriate phenotype for the competitive or mate choice environment that an individual encounters when mature. There are numerous theoretical and empirical examinations of the role of the social environment on the strength and direction of selection. However, only a handful of empirical studies examine how the social environment affects juvenile allocation and whether such tactics are adaptive. The goal of this review is to synthesize current knowledge about socially cued anticipatory plasticity, including the sensory modalities that individuals use to predict the adult competitive and mating environment. We then outline the various factors that are necessary for the evolution of socially cued anticipatory plasticity and discuss how this can affect phenotypic evolution. We conclude by suggesting some directions that future studies should take in order to understand how social variation can alter selection and the evolution of development.

Phenotypically plastic mating behavior may allow males to modify their reproductive behavior to suit the prevailing social conditions, but we do not know if males only react to immediate social stimuli or change their inherent mate preferences according to their social history. Here we examine the effect of social experiences on the subsequent reproductive behavior of male guppies under standard conditions, allowing us to distinguish the effect of past and immediate social conditions. Males experienced experimental conditioning periods during which they interacted with three females, either of variable size or of similar size. Females arrived either simultaneously or consecutively. In subsequent standard assays, only males that had experienced females of variable size preferentially courted large females. Further, males exposed to sequential female arrival courted subsequent females more vigorously than males that had experienced simultaneous female arrival. In contrast, males did not alter their coercive mating attempts in relation to their recent social history. These results demonstrate that males use past experiences to modify their subsequent reproductive behavior rather than reacting only to immediate stimuli, and reveal the sophisticated ways in which males alter their reproductive tactics to suit the social environment and maximize fitness across changing selective landscapes.

Human mate choice research often concerns sex differences in the importance of traits such as physical attractiveness and social status. A growing number of studies indicate that cues to social context, including other people who appear in stimulus photographs, can alter that individual's attractiveness. Fewer studies, however, consider judgements of traits other than physical attractiveness, such as wealth. Here we manipulate the presence/absence of other people in photographs of target models, and test the effects on judgments of both attractiveness and earnings (a proxy for status). Participants (N = 2044) rated either male or female models for either physical attractiveness or social/economic status when presented alone, with same sex others or with opposite sex others. We collectively refer to this manipulation as 'social context'. Male and female models received similar responses for physical attractiveness, but social context affected ratings of status differently for women and men. Males presented alongside other men received the highest status ratings while females presented alone were given the highest status ratings. Further, the status of females presented alongside a male was constrained by the rated status of that male. Our results suggests that high status may not directly lead to high attractiveness in men, but that status is more readily attributed to men than to women. This divide in status between the sexes is very clear when men and women are presented together, possibly reflecting one underlying mechanism of the modern day gender gap and sexist attitudes to women's economic participation. This adds complexity to our understanding of the relationship between attractiveness, status, and sex in the light of parental investment theory, sexual conflict and economic theory.

Most research on life span and aging has been based on captive populations of short-lived animals; however, we know very little about the expression of these traits in wild populations of such organisms. Because life span and aging are major components of fitness, the extent to which the results of many evolutionary studies in the laboratory can be generalized to natural settings depends on the degree to which the expression of life span and aging differ in natural environments versus laboratory environments and whether such environmental effects interact with phenotypic variation. We investigated life span and aging in Telostylinus angusticollis in the wild while simultaneously estimating these parameters under a range of conditions in a laboratory stock that was recently established from the same wild population. We found that males live less than one-fifth as long and age at least twice as rapidly in the wild as do their captive counterparts. In contrast, we found no evidence of aging in wild females. These striking sex-specific differences between captive and wild flies support the emerging view that environment exerts a profound influence on the expression of life span and aging. These findings have important implications for evolutionary gerontology and, more generally, for the interpretation of fitness estimates in captive populations.