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Investigations of women’s same-sex relationships present a paradoxical pattern, with women generally disliking competition, yet also exhibiting signs of intrasexual rivalry. The current article leverages the historical challenges faced by female ancestors to understand modern women’s same-sex relationships. Across history, women were largely denied independent access to resources, often depending on male partners’ provisioning to support themselves and their children. Same-sex peers thus became women’s primary romantic rivals in competing to attract and retain relationships with the limited partners able and willing to invest. Modern women show signs of this competition, disliking and aggressing against those who threaten their romantic prospects, targeting especially physically attractive and sexually uninhibited peers. However, women also rely on one another for aid, information, and support. As most social groups were patrilocal across history, upon marriage, women left their families to reside with their husbands. Female ancestors likely used reciprocal altruism or mutualism to facilitate cooperative relationships with nearby unrelated women. To sustain these mutually beneficial cooperative exchange relationships, women may avoid competitive and status-striving peers, instead preferring kind, humble, and loyal allies. Ancestral women who managed to simultaneously compete for romantic partners while forming cooperative female friendships would have been especially successful. Women may therefore have developed strategies to achieve both competitive and cooperative goals, such as guising their intrasexual competition as prosociality or vulnerability. These historical challenges make sense of the seemingly paradoxical pattern of female aversion to competition, relational aggression, and valuation of loyal friends, offering insight into possible opportunities for intervention.

Here, we present a mechanistically grounded theory detailing a novel function of the behavioral immune system (BIS), the psychological system that prompts pathogen avoidance behaviors. We propose that BIS activity allows the body to downregulate basal inflammation, preventing resultant oxidative damage to DNA and promoting longevity. Study 1 investigated the relationship between a trait measure of pathogen avoidance motivation and in vitro and in vivo proinflammatory cytokine production. Study 2 examined the relationship between this same predictor and DNA damage often associated with prolonged inflammation. Results revealed that greater trait pathogen avoidance motivation predicts a) lower levels of spontaneous (but not stimulated) proinflammatory cytokine release by peripheral blood mononuclear cells (PBMCs), b) lower plasma levels of the proinflammatory cytokine interleukin-6 (IL-6), and c) lower levels of oxidative DNA damage. Thus, the BIS may promote health by protecting the body from the deleterious effects of inflammation and oxidative stress.

People tend to befriend others similar to themselves, generating a pattern called homophily. However, existing studies on friendship patterns often rely on surveys that assess the perspective of relatively few participants on their friendships but do not measure actualized friendship patterns. Here, we used data from a large Slovakian online social network to assess the role of gender, age, and body mass index (BMI) in same-gender online connections among more than 400,000 users. We found that age and BMI homophily occurred in both men’s and women’s same-gender connections, but somewhat more strongly among men’s. Yet, as women diverged in BMI, their connections were less likely to be reciprocated. We discuss how the evolutionary legacy of men’s coalitional competition (e.g., warfare) and women’s mating competition or recruitment of allocare providers might contribute to these patterns in modern same-gender relationships. For example, men’s engagement in physical activities may lead to similar formidability levels among their same-gender peers. Altogether, our findings highlight the importance of trait similarity to same-gender friendship patterns.

The current investigation examined whether women’s perceptions of the sex ratio (ratio of women to men) in the local population influence their body dissatisfaction and weight loss motivations. A higher ratio of women to men in a given population signifies a relative abundance of same-sex mating competitors, intensifying female intrasexual competition. Five studies ( N  = 1,776) tested the hypotheses that women’s perceptions of a female-skewed sex ratio would correspond to increased feelings of intrasexual competitiveness and perceptions of unfavorable mating prospects, which would, in turn, be associated with heightened body dissatisfaction and weight loss motivations. Among university and community women (Studies 1and 2), perceptions of a female-skewed sex ratio corresponded to greater intrasexual competitiveness, increased body dissatisfaction, and increased dieting inclinations. Among single women, assessments of a female-skewed sex ratio corresponded to perceptions of unfavorable mating prospects, increased romantic pressure to alter their appearance, and higher body dissatisfaction (Study 3). Studies 4 and 5 experimentally manipulated perceived sex ratio. Women in the female-skewed condition felt less satisfied with their weights and shapes, but only if they believed the manipulation (Study 4). In Study 5, using a within-subjects design, women who evaluated a male-skewed (vs. female-skewed) dating profile array subsequently desired to lose less weight. Findings suggest women’s perceptions of their social environments may contribute to body image and dieting motivations.

Depression, anxiety, and loneliness have long been recognized as global mental health concerns. To temporarily relieve psychological distress, self-soothing behavior is common, including engagement in sexual behaviors that are linked to positive mental well-being. Considering the COVID-19 pandemic further exacerbated many mental health ailments alongside physical distancing regulations, we specifically examined online sexual behavior via the use of emergent digital sexual technologies, or sextech. In a 2019 study of 8004 American adults, we assessed whether people experiencing higher anxiety, depression, and/or loneliness were more likely to engage in sextech use. Furthermore, we examined whether anxiety or depression mediated the association between loneliness and sextech use, as loneliness is one contributor to anxiety and depression. People with higher anxiety and depression were more likely to engage in sextech. However, those who were more lonely were less likely to engage with sextech, suggesting the aforementioned patterns were not due to lack of social connection. Our findings suggest people with mental health struggles may be drawn to interactive, digital forms of sexual behavior as a means of alleviating symptoms through distraction or self-soothing. This insight offers an important pathway for expanding the scope of mental health interventions, particularly as technology becomes increasingly prevalent and accessible in everyday life.

Research on women's competition, indirect aggression, and gossip has uncovered a perplexing pattern: women deny their own competitiveness and gossip, but openly acknowledge that of other women. The current investigation proposed one solution to this paradox: women's unawareness of their competitive and malicious motivations grants a competitive advantage in female intrasexual reputation competition. Gossipers who express concern for their targets can preserve their own social desirability while simultaneously transmitting information that harms their target's reputation. Two online studies tested this theory by examining the prevalence and efficacy of concern motivations within gossip. Study 1 tested the prediction that women would assert greater concern relative to malicious motivations for gossiping by comparing male and female participants' perceptions of their own and others' social conversation motivations. Indeed, compared to men, women endorsed stronger concern motivations and lower reputation-harming motivations when gossiping. Moreover, women were especially likely to assert benevolent intentions when discussing same-sex peers compared to men, suggesting these motivations characterize women's gossip about same-sex rivals. Study 2 tested the competitive efficacy of ostensible concern motivations. Male and female participants evaluated female gossipers and their targets across three hypothetical gossip scenarios. The framing of the gossiper's statement was experimentally manipulated such that she delivered her information with concern, with malice, or neutrally. Consistent with predictions, gossip delivered with concern enhanced perceptions of the gossiper's trustworthiness, interpersonal desirability, and romantic desirability compared to gossip delivered neutrally or maliciously. Taken together, these findings suggest women's belief in their prosocial motivations for gossiping is a socially advantageous strategy for female intrasexual reputation competition.

When standing, intrinsic ankle stiffness is smaller when measured using large perturbations, when sway size is large, and when background torque is low. However, there is a large variation in individual intrinsic ankle stiffness. Here we determine if individual variation has consequences for postural control. We examined the relationship between ankle stiffness, ankle torque and body sway across different individuals. Ankle stiffness was estimated in 19 standing participants by measuring torque responses to small, brief perturbations. Perturbation sizes of 0.2 & 0.9 degrees (both lasting 140 ms) measured short- and long-range stiffness respectively, while participants either stood quietly on a fixed platform or were imperceptibly tilted to reduce stability (0.1 Hz sinusoid; 0.2 & 0.4 deg). The spontaneous body sway component (natural random relatively rapid postural adjustments) and background ankle torque were averaged from sections immediately before perturbations. The results show that, first, intrinsic ankle stiffness is positively associated with ankle torque, and that this relationship is stronger for long-range stiffness. Second, intrinsic ankle stiffness is negatively associated with body sway, but, in contrast to the relationship with torque, this relationship is stronger for short-range stiffness. We conclude that high short-range intrinsic ankle stiffness is associated with reduced spontaneous sway, although the causal relationship between these two parameters is unknown. These results suggest that, in normal quiet standing where sway is very small, the most important determinant of intrinsic ankle stiffness may be stillness. In less stable conditions, intrinsic ankle stiffness may be more dependent on ankle torque.