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ObjectiveA growing body of research has begun investigating the relationship between hormones and female competitiveness. Many researchers have focused on the effect of the menstrual cycle and hormonal contraceptives. Despite many attempts at understanding hormone-behavior associations, contradictory findings have made it difficult to determine the existence of true effects. The aim of the current research was to use a robust methodological design to investigate the effect of fertility probability on four competitive orientations in naturally cycling women and hormonal contraceptive users.MethodsUsing a longitudinal diary study with over 3,900 observations from 21 countries, we explore the effect of fertility probability on four self-report competitive orientations after controlling for menstruation: self-developmental competition, hyper competitiveness, competition avoidance, and lack of interest toward competition.ResultsUsing Bayesian estimation for ordinal mixed models, we found that fertility probability was associated with an increase in self-development competitiveness amongst naturally cycling women but not hormonal contraceptive users. We also found weak evidence that hormonal contraceptive users show reduced interest in competing compared to naturally cycling women. There were no other robust effects of fertility or hormonal contraceptive use.ConclusionsThese results suggest that fertility probability is associated with increased fluctuations in self-development competitive motivation and that hormonal contraceptives interfere with this effect. This research contributes to the growing body of literature suggesting that hormonal contraceptives may influence psychology and behavior by disrupting evolved hormonal mechanisms.

Does dieting intensify during Spring? Previous research suggests that body dissatisfaction is seasonal and peaks during Summer. Extending these findings to seasonal dieting, we contend that individuals' apprehensions about heightened Summertime body dissatisfaction motivate Springtime dieting. To detect seasonal dieting, we examined the seasonal frequencies of 69 dieting hashtags within a database of 564 million tweets originating from the United States and spanning eight calendar years (2012-19). In total, we detected 628,355 dieting hashtags. Of these, 30% occurred during Spring, 20% during Autumn/Fall, and 25% during each of Summer and Winter. During Spring, there were ~64,000 additional dieting hashtags compared with Autumn/Fall, and ~32,000 additional hashtags compared with Summer and Winter. Of the nine most common dieting hashtags that together accounted for 96% of the total, all nine peaked during Spring (ps 0.0001). This Spring-centric pattern was apparent for both appearance-oriented diets (e.g., "atkins" and "weightwatchers") and ostensibly non-appearance-oriented diets (e.g., "vegan" and "glutenfree"), suggesting that non-appearance-oriented diets might nonetheless be co-opted for appearance-oriented purposes. In conclusion, we found credible evidence that dieting intensifies during Spring. Future research should examine whether eating disorders and muscle dysmorphia also intensify during Spring because dieting is intrinsic to both these conditions.

High economic inequality has been identified as a key factor in fuelling political polarization, but the underlying psychological mechanisms behind this phenomenon are not well understood. We propose that economic inequality threatens people's experience of social order and control, leading them to adopt moralistic mindsets – yet this mindset may sow divisions in society. Using data from social media, a multinational survey across 41 regions around the world, and an experimental approach, our work shows that economic inequality is associated with the use of moral language online, harsher moral judgments, and a desire for clearer social and moral rules in society. Together these findings demonstrate that economic inequality is linked to the tendency to see the world through a moral lens. Understanding how societal structures impact our moral perspectives may help us bridge the growing divisions between people and foster a more united society.

The distribution of financial resources, and especially the magnitude of inequalities in resource distributions, exert profound effects on individual behavior. Evolutionary theorists have proposed that these associations may stem from the influence of inequality on mating competition (e.g., Daly & Wilson, 1988, 1990; Daly, 2016). Mating markets are subject to fluctuating supply and demand, often creating competition between and within the sexes. For instance, as income inequality increases, poorer men are less able to attract mates using their financial resources (Brooks, Blake, & Fromhage, 2022), limiting their reproductive success and motivating competition among men. Such ecologies account for the association between economic inequality and misogynistic Incel ideology in the United States (Brooks, Russo-Batterham, & Blake, 2022). In this pre-registration, we propose to use pre-existing Gender Harmony Project data to investigate how poor mating market conditions affect the beliefs of men and women concerning gender. Specifically, we look at both genders' beliefs regarding precarious manhood and zero-sum gender equality, and gender self-construal discrepancies under conditions of economic inequality, and as a function of gender and SES.

Evolutionary psychologists argue that infidelity benefits men by increasing their offspring quantity, but the benefits of infidelity to women are the subject of intense debate. The two leading theories both focus on quality: The good genes (GG) hypothesis posits infidelity evolved in women to pair the better genes of an affair partner with the paternal investment of a primary partner, whereas the mate-switching (MS) hypothesis argues women’s affairs help them trade to a more desirable primary partner. Minimal empirical work has been done to contrast these theories, and they share major challenges: The paradigm undergirding them is in question, and alternative hypotheses are gaining empirical traction. In this context, we plan to test the MS and GG hypotheses against each other and their alternatives. Both theories explicitly predict that women will perceive their affair partners as more desirable, but they make different predictions as to how. Our planned study is an online survey of men and women recently engaged in affairs, using four Likert-style instruments designed to measure how desirable they find their mates. If the focus of the mainstream debate is justified, and women are indeed “cheating up,” women, more than men, should find their extra-pair mate more desirable than their in-pair mate on at least one scale. Different scales are expected to exhibit this preference depending on whether women’s affairs are to obtain genes or a new mate. Results of this study will forward the debate regardless, either by challenging its assumptions or by distinguishing its frontrunners.

Biological predictors of human dominance are hotly contested, with far-reaching implications for psychological sex differences and the placement of men and women in the social hierarchy. Most investigations have focused on dominance in men and testosterone, with diminished attention paid to dominance in women and other biological mechanisms. Investigating biological influences on other routes to status attainment popular among women—such as via prestige in addition to dominance—have also been neglected. Here, I examined whether status seeking via prestige and via dominance covaried with fertility probability in a citizen science project spanning 14 countries and 4 world regions. Across 4,179 observations, participants tracked their menstrual cycle characteristics, motivation for prestige and dominance, dominance contest outcomes, and three domains of self-esteem. Self-esteem is predicted by status within a group and helps individuals navigate social hierarchies. Bayesian mixed models controlling for menstruation indicated that the motivation to obtain status via prestige but not dominance peaked when conception was most likely, as did dominance contest losses and two self-esteem domains. Fertility appears to reorient female psychology toward prestige-based strategies to success, enhancing women’s desire for social capital through influence and admiration but not through fear, coercion, or intimidation. These insights fundamentally advance the understanding of the biological correlates of status seeking among women. They further suggest that fertility motivates not only mating competition but gaining rank and positive regard in social hierarchies.

Differences in attitudes on social issues such as abortion, immigration, and sex are hugely divisive, and understanding their origins is among the most important tasks facing human behavioural sciences. Despite the clear psychological importance of parenthood and the motivation to provide care for children, researchers have only recently begun investigating their influence on social and political attitudes. Because socially conservative values ostensibly prioritize safety, stability, and family values, we hypothesized that being more invested in parental care might make socially conservative policies more appealing. Studies 1 (pre-registered; n=376) and 2 (n=1,913) find novel evidence of conditional experimental effects of a parenthood prime, such that people who engaged strongly with a childcare manipulation showed an increase in social conservatism. Study 2 also finds evidence that this effect is mediated by increases in parental care motivation. Study 3 (n=2,610, novel data from 10 countries) and 4 (n=426,444, World Values Survey data) find evidence that both parenthood and parental care motivation are associated with increased social conservatism around the globe. Further, most of the positive association globally between age and social conservatism is accounted for by parenthood. These findings support the hypothesis that parenthood and parental care motivation increase social conservatism.

Salivary steroid immunoassays are widely used in psychoneuroendocrinological studies of menstrual cycle phase, puberty, and menopause. Though manufacturers advertise their assays as suitable, they have not been rigorously validated for these purposes. We collated data from eight menstrual cycle studies across >1,200 women and >9,500 time points. Seven studies collected saliva and one collected serum. All assayed estradiol and progesterone and had an independent measure of cycle phase (LH-surge, menstrual onset). In serum, cycle phase measures strongly predicted steroid concentrations. In saliva, cycle phase poorly predicted estradiol values, which showed an upward bias compared to expectations from serum. For salivary progesterone, predictability from cycle phase was mixed. Widely used enzyme-linked assays performed poorly, while LC-MS/MS performed better. Imputing the population-average serum steroid changes from cycle phase may yield more valid values of hormonal changes for an independent person than directly assessing their hormone levels using salivary immunoassays.

Economic inequality brings multiple adverse consequences. These range from decreased trust in government, increased drug abuse and violence, and decreased societal cohesion. If and how economic inequality impacts online behaviors has received less attention. Here, we use a corpus of 6 million race tweets posted between 2012 and 2018 to determine the frequency and sentiment of tweets containing ethnic epithets and slurs across all 52 US states. Informed by Integrated Threat Theory, we tested whether inequality increased the use of slurs on social media for the purpose of denigrating other ethnic groups. Consistent with this, we found that states with greater inequality predicted increased use of racial epithets used to denigrate other groups. However, we also found that more unequal locales were positively correlated with increased use of ethnic words used in a positive way (potentially toward other ingroup members). As such, while inequality is correlated with more prejudicial behavior on social media, it may also increase the salience of ethnic group identity more broadly. Implications and future directions are discussed.

Women are more likely than men to be sexualized, objectified, and dehumanized. Female sex workers experience stigma and violence associated with these judgements at far higher rates than other women. Here, we use a pre-registered experimental design to consider which aspects of sex work – the level of sexual activity, earned income, or perceived autonomy of the work – drive dehumanization. A first group of participants (N = 217) rated 80 vignettes of women varying by full-time employment, hobbies and interests on humanness. These ratings were subtracted from the ratings of a second group of participants (N = 774) who rated these same vignettes which additionally described a part-time job, hobby or activity that varied in sexual activity, income earned and autonomy over one’s actions. We find that women and especially men dehumanize women they believe are engaging in penetrative sex. We also find that women’s autonomy of, but not their income from, their sexual activity increases dehumanization. Our findings suggest that opposition to women’s ability to pursue casual sex and generalizations about the exploitative conditions of sex work may drive the harshest negative prejudice towards female sex workers and, by similar mechanisms, women’s sexuality in general.