Progestin-only birth control (e.g., hormonal IUD) does not contain ethinylestradiol (EE), the synthetic estrogen found in combined hormonal contraceptives (ChCs) (e.g., oral pill). Ethinylestradiol has been linked to relationship jealousy; however, it suppresses testosterone, a hormone implicated in intrasexual competitiveness. This study examined the relationship between contraceptive type and self-reported intrasexual competitiveness and jealousy, with the goal of identifying practical differences among existing groups of contraceptive users. A between-subjects design compared combined hormonal contraceptive users, progestin-only contraceptive users, and non-users on self-reported intrasexual competition and jealousy. Participants (N = 398) reported contraceptive information and then completed Buunk and Fisher’s (Journal of Evolutionary Psychology, 7(1), 37-48, 2009) intrasexual competitiveness scale and Buunk’s (Personality and Individual Differences, 23(6), 997-1006, 1997) jealousy scale. Hormonal contraceptive users reported slightly higher levels of jealousy than non-users (p = .012, η2 = 0.01), but the difference between contraceptive types was not significant (p = .098, η2 = 0.01). Among levonorgestrel users, combined hormonal contraceptive users reported significantly higher jealousy than progestin-only contraceptive users (p = .012, η2 = 0.08), although practical differences were small. No dosage effects of ethinylestradiol on jealousy were found. No relationship between contraceptive type and intrasexual competition was found. Combined-hormonal contraceptive users may experience greater relationship jealousy than non-users and potentially progestin-only users. Differences may only be practically meaningful for specific populations. Further research is necessary to standardize the route of administration and explain the null findings regarding intrasexual competition. Our findings provide a basis for future research that can inform contraceptive choice.
The aim of the study was to determine whether there were any differences in women’s evaluations of facial masculinity, beardedness, body shape and muscularity according to their age and menopausal status. The women assessed warp-modified photographs of a man in which the prominence of his secondary sexual characteristics was altered in three areas of evaluation: physical attractiveness, degree of aggression and social dominance. The material consisted of 122 Polish women, aged 19–70 years (mean age: 45.6 y., SD = 15.1 y.), representing three menopausal stages: premenopause, perimenopause and postmenopause. Significant differences in women’s assessments were found. Both age and menopausal status had a significant impact on the rating of physical attractiveness. Older women rated men with medium and full facial hair as more attractive, while menopausal status had no effect. Postmenopausal women rate V shaped bodies as less attractive. Women’s age had no effect on their ratings of male body shape attractiveness. Older women rated men with light muscularity as more attractive than younger women. No effect on menopausal status was found. There was no significant effect of age nor menopausal status on ratings of aggression and social dominance. The degree of development of the secondary sexual characteristics is an important biological signal to others in the population, as it indicates the biological fitness of the individual. A man with outstanding sexual characteristics is perceived by women as a carrier of ‘good genes’, which indicates his readiness to undertake the parental investment.
Climate variation during the Late Pleistocene and Holocene may have shaped human behavioral evolution through selection on personality-related genetic variants. However, direct evidence for climatically driven selection on behavioral polygenic scores (PGS) remains limited. We tested for climate-linked selection on behavioral PGS using modern global genomes and ancient DNA from Western and Eastern Eurasia. PGS were computed for Extraversion, Agreeableness, and Neuroticism, and temporal trends were modeled with hinge regressions at 12,000 and 19,000 years before present (BP), adjusting for latitude and genomic coverage. In Eastern Eurasia, ancestry components were used to predict trait scores within the Holocene period. In modern populations, all three traits exhibited latitude-associated differentiation, consistent with cold-climate adaptation. In Western Eurasian ancient genomes, Extraversion and Neuroticism declined with sample age before the Last Glacial Maximum (pre-knot slopes ≈ −0.018 and −0.045 to −0.051 SD/kyr), then reversed direction after 12–19k BP (Δβ ≈ +0.036 to +0.104, all p < 0.001), suggesting post-LGM relaxation of selection. Agreeableness showed the complementary trend, increasing before and attenuating after the knots. A latent factor summarizing higher Agreeableness and lower Extraversion/Neuroticism captured these coordinated population-level shifts (Δβ ≈ −0.17, p < 0.001). In Eastern Eurasia, Holocene ancestry components (e.g., Jōmon, Tibetan, Northeast Chinese) predicted trait scores consistent with Arctic adaptation, while latitude effects weakened after accounting for admixture. Both trait-specific and factor-level analyses indicate that Late Pleistocene cold climates intensified selection against Extraversion and Neuroticism while favoring Agreeableness, with Holocene warming leading to a reversal or relaxation of these pressures. These results support a model of climate-driven directional selection on behavioral tendencies across the Late Quaternary.
Some researchers have suggested that longer eyelashes may serve as a sexually selected cue to underlying immunocompetence, based on findings that individuals with longer eyelashes are rated as more attractive and healthier. Yet no prior research has directly tested whether eyelash morphology is associated with health symptoms or biological markers of immune function. In the present study, participants (N= 163, ages 18–38) provided eyelash samples(measured for total length and lash length-to-eye-width ratio), self-reported health data, saliva samples (assayed for immunoglobulin A and cortisol), and blood samples (assayed for serum lysozyme and lactoferrin). Results indicate no significant associations between eyelash morphology and any of the measures of underlying health and immunocompetence. Together, these findings do not support the hypothesis that eyelash morphology has been sexually selected as a reliable cue of underlying immunocompetence, but that it may provide a cue to age.
T helper (Th) 1 and Th2 cells are crucial in mediating immune responses, with their balance influenced by factors such as age, body mass index (BMI), and estradiol (E2) levels. This study investigates the IFN-γ/IL-10 ratio across different demographic and physiological variables to understand how these factors may interact and impact immune function. Serum levels of E2, IFN-γ, and IL-10 were measured in a community-based cross-sectional study involving 238 women and 143 men in Texas, USA. Participants completed a comprehensive survey on demographics, health status, and reproductive history. Multiple linear regression models assessed the relationships between the IFN-γ/IL-10 cytokine ratio and variables such as age, BMI, and reproductive status, with particular attention to sex differences and menopausal status. The study found that females had a higher IFN-γ/IL-10 cytokine ratio compared to males. The IFN-γ/IL-10 ratio increased with age in both sexes and was positively associated with BMI in females. Estradiol levels were negatively correlated with the IFN-γ/IL-10 ratio, suggesting that higher estrogen levels may shift the balance toward IL-10 dominance. These patterns were consistent across pre- and post-menopausal women, indicating that age, BMI, and E2 levels play similar roles regardless of reproductive status. These findings provide new insights into the dynamic regulation of the IFN-γ/IL-10 balance, particularly highlighting the complex interactions between sex hormones and immune function across the lifespan.
Close female friendships provide emotional security and stress buffering, particularly during emerging adulthood, a life stage marked by heightened competition across life domains (e.g. academics; relationships). Yet, these relationships are also uniquely fragile, especially when status differences emerge between friends. The current study examined women’s emotional and physiological responses to imagined performance differences with a close same-sex friend. Eighty-one undergraduate women (Mage = 20.15) were randomly assigned to one of three conditions: outperform, equal performance, or underperform relative to a close friend in a self-selected life domain. Emotional responses, anticipated friend reactions, and physiological stress, measured via respiratory sinus arrhythmia (RSA), were recorded. As predicted, participants reported the greatest happiness and lowest expectations of negative emotion from their friend in the equal performance condition. RSA decreased significantly during the imagined competition phase, indicating physiological stress, and rebounded during recovery. A marginal interaction between time and hormonal birth control use revealed that naturally cycling women exhibited lower RSA, suggesting higher physiological stress, across all phases compared to those using hormonal contraception. These findings suggest that even hypothetical status differences with close friends can elicit measurable stress responses in women. Because ovulation was not directly assessed and hormonal profiles were not measured, interpretations regarding hormonal status should be viewed as preliminary. Results highlight the social and physiological costs of competition in female friendships and offer insight into the evolved trade-offs women navigate between affiliation and status. Not applicable.
Burnout is a pandemic and costly public health problem. Studies link leadership and peer behavior to burnout, but explanations are constrained to proximate mechanisms. Evolutionary models describe depression as an ancient appeasement response to avert dangerous physical conflict with higher-ranking group members and coalitions. In turn, psychometric research consistently finds high construct overlap between burnout and depression. This shared phenomenology suggests that burnout in response to workplace social stressors reflects appeasement. The purpose of the current study is to test the relationship between rank and competition related variables and burnout. Participants (N = 256) completed an online survey comprised of burnout and rank-related variables. Domineering leadership, self-perceived low rank, negative workgroup gossip, and perceptions of physical vulnerability predicted burnout. Negative workgroup gossip mediated the relationship between dominant leaders and burnout. Results suggest that occupational burnout may be rooted in an ancient appeasement response to powerful individuals and coalitions. Clarifying evolutionary mechanisms of burnout can inform prevention and treatment, while deepening our understanding of burnout as a construct.
Moral decision-making often involves interpersonal interactions in which individuals seek to influence others’ moral judgments. The present hyperscanning study aimed to examine whether the alignment of moral decision-making style (emotional vs. cognitive) between two individuals modulates neural and autonomic synchronization during a moral persuasion task. Fourteen pairs of individuals were categorized as either homologous (same style) or heterologous (different styles) based on their responses to a real-life moral dilemma. During the task, one individual (Pder) attempted to persuade the other (Pdee) of the superiority of their own moral justification, while EEG activity across five frequency band (delta, theta, alpha, gamma and beta) and autonomic signals (SCL, HR, HRV) were simultaneously recorded. Neural and physiological synchrony was analyzed using a dissimilarity index based on Euclidean distance. EEG results revealed no significant differences between homologous and heterologous pairs, although dissimilarity in the delta band was significantly higher in frontal regions than in temporo-central and parieto-occipital areas. In contrast, autonomic results revealed greater SCL dissimilarity in heterologous pairs, indicating reduced emotional synchrony when moral styles diverge. These findings suggest that, while cortical synchrony may be more strongly shaped by the task demands and structure, shared moral orientations may promote greater peripheral affective alignment.
Psychology and social science research offer some promising work in the field of decision-making science. However, given the qualitative nature of much of this research, understanding some physiological bases of decision-making may assist by providing more objectivity. The purpose of this study, therefore, was to explore hormonal and neurophysiological biomarkers of stress relative to strategic decision making, with and without an accompanying exercise stress. Twenty-one competitive male chess players were recruited to this study. On two separate occasions prefrontal cortex (a brain region involved in executive decision making which is sensitive to stress) hemodynamics were measured while participants played a standardized game of chess against a computer bot, once after exposure to a physical stressor (experimental condition) and once without (control condition). Participant’s stress hormones (testosterone and cortisol) were also measured in the morning of each test and immediately prior to the game of chess. Participants were more likely to win under experimental conditions. Interestingly, there was no difference between conditions for baseline testosterone and cortisol concentrations, and the exercise protocol did not elicit a hormonal change. However, significant differences were observed for prefrontal cortex hemodynamics following the physical stressor (vs. control condition), and changes in prefrontal cortex hemodynamics were observed as games progressed (p ≤ 0.034). Our results speculatively suggest several independent pathways exist to explain how stress affects decision making. This work opens several vistas for future research exploring decision making using neurohormonal/physiological biomarkers.
This study experimentally tested the impact of perceived physical resemblance on ascriptions of close relationships between individuals. Following kin selection theory, if physical resemblance is a proxy for genetic relatedness, it is adaptive to act altruistically toward similar-looking individuals who may share genes in common, yet select dissimilar-appearing romantic partners to avoid mating that may result in inbreeding depression or lack of offspring diversity. Participants were shown sets of paired facial photos of two persons varying in physical resemblance to one another, who were labeled as being either friends, siblings, or romantic partners. Raters evaluated the closeness of each pair’s relationship based on their pictures. Another set of raters was shown the same pairs of photos without relationship labels and was asked to evaluate how likely they thought the pairs were siblings, friends, or romantic partners, respectively. Across all conditions, pairs exhibiting greater perceived physical resemblance were rated as having closer/higher-quality relationships and were more likely thought to be siblings or friends, but were less likely seen as romantic partners. Similar patterns were found when participants (n = 526) were asked about their own personal relationships; generally, ratings of both perceived physical and behavioral similarity were positively associated with perceived relationship closeness across all relationship types, even when controlling for factors such as relationship length and residence distance. In line with kin selection theory, participants ascribed closer relationships to those who appeared more genetically related but were less likely to identify similar-looking pairs as being romantic partners.
Aggressive behavior is influenced by genetic factors, but findings in behavioral genetics remain inconsistent due to heterogeneous study samples. This study aims to investigate the relationship between aggression traits and polymorphisms of AR, HTR2A, and OXTR genes in a monoethnic sample of Armenian university students, and to compare the results with previously studied African and Siberian populations. The study included 231 Armenian students. Aggression levels were assessed using the Buss-Perry Aggression Questionnaire and proactive/reactive aggression scales. Genetic analysis focused on the OXTR-rs53576, HTR2A-rs6311, and AR(CAG)n polymorphisms. The distribution of alleles was examined, and associations between genetic variations and aggression traits were analyzed, considering sex differences and gene–gene interactions. Men exhibited significantly higher levels of physical (p = 2.8e-8), proactive (p = 2.8e-8), and reactive aggression (p = 0.015), while hostility was more pronounced in women (p = 0.033). In women, OXTR-rs53576 interacted with AR(CAG)n to influence reactive aggression (p = 0.015). In men, AR(CAG)n independently affected physical aggression (p = 0.003), and its interaction with OXTR-rs53576 also influenced physical aggression (p = 0.005). Combined analysis revealed that AR(CAG)n and OXTR-rs53576 interactions were associated with verbal aggression (p = 0.008), anger (p = 0.035), and reactive aggression (p = 0.029). Our findings suggest that genetic variations in AR and OXTR contribute to individual differences in aggression, with sex-specific effects and gene–gene interactions playing a significant role. In a comparative context, Armenians demonstrate intermediate levels of aggression between highly egalitarian and patriarchal societies, reinforcing the importance of both genetic and sociocultural factors in the expression of aggression.
This study examines the complex dynamics of father-daughter relationships, focusing on how life history factors are associated with paternal behaviors towards daughters. Drawing on Life history Theory and the Daughter-Guarding hypothesis, the research investigates how these factors contribute to father-daughter interactions, such as attachment, protection, support, and control received from fathers. Two surveys were conducted: one with 120 daughters aged 18–21 (Study 1) and another with 120 fathers (Study 2), both recruited through online platforms. Study 1 examined the relationship from the daughters’ perspective, while Study 2 explored it from the fathers’ perspective. Fathers with higher education and stable financial backgrounds showed stronger attachment, support, and protection to their daughters. Additionally, daughters’ self-perceived attractiveness was associated with paternal behaviors, suggesting that attractive daughters were more likely to receive support, protection, and develop stronger attachments to their fathers. The findings emphasize the need for further research into the relationships of these factors, particularly across diverse cultural and socioeconomic backgrounds, to better understand their role in shaping father-daughter relationships and the potential effects on female development.
Competence and prosociality of the person being helped are important indicators for ensuring a return on help, as reciprocity would not be possible if the person being helped lacked either the competence or the inclination to reciprocate in the future. A previous study that measured compassion using a Likert scale found that the controllability of the cause of the difficulty and the level of the sufferer’s prosociality independently influenced the degree of compassion. In this study, we aimed to examine how the probability of reciprocity affects physiological responses (such as heart rate), as well as psychological responses, to the suffering of others. Participants’ heart rates were monitored while they watched a video of a man monologuing about his difficulty. Compassion was also measured using a Likert scale. In Study 1, we investigated the effect of the controllability of the difficulty on heart rate. In Study 2, we provided participants with additional information about the prosociality of the man in the video. Controllability affected compassion ratings, replicating the results of previous studies. Although participants’ heart rates decreased when they learned that the man was suffering, the controllability of the cause did not influence the degree of decline. The results suggest that people experience compassion at a physiological level, while the controllability of the difficulty (i.e., a cue for reciprocity) is processed subjectively and reflected only in consciously reported psychological measures, which may reflect the evolutionary history of compassion.
Infectious diseases have posed an existential threat to humans throughout history, resulting in a complex system of evolved psychological and behavioral mechanisms designed to help mitigate infection. Given that food consumption represents a significant route through which humans can be exposed to illness-causing pathogens, further research into the relationship between disease avoidance motivations and novel food avoidance (i.e., food neophobia) is warranted. Across three studies (total N = 736), we investigated the relationship between trait disease avoidance motivation (assessed by the Perceived Vulnerability to Disease scale) and food neophobia. Results from each of the three studies indicated that greater dispositional germ aversion significantly predicted greater food neophobia, whereas the relationship between dispositional perceived infectability and food neophobia was positive but more variable across the studies. Additionally, Study 3 revealed that while greater dispositional food neophobia predicted greater likelihood of avoiding foreign foods, experimentally priming disease threat was not associated with food choice. Lastly, an internal meta-analysis revealed that both germ aversion and perceived infectability were both uniquely positively associated with food neophobia. Limitations, conceptual issues, and avenues for future research are discussed.
Research using system integrity theory (SIT) has shown that more intelligent men have higher-quality semen, which is puzzling because although reproductive capability should predict fertility, more intelligent men have fewer children. The current research addresses this puzzle by highlighting the distinct obligate and facultative outcomes that emerge when SIT is integrated with life history theory (LHT) and evolutionary novelty theory (ENT). Specifically, we propose that SIT accounts for more rigidly obligate physiological traits whereas LHT encompasses both obligate traits and flexibly facultative behaviors and, thus, permits the ENT-driven expectation that brighter individuals would act in evolutionarily novel ways—e.g., slower reproduction despite possessing capacities for faster reproduction. We examined this logic using another obligate reproductive trait: the timing of puberty. Based on our proposed synthesis of SIT, LHT, and ENT, we tested the prediction that more intelligent people would experience puberty earlier and yet have sex later, engage in less sexual activity, and have fewer children using two nationally representative and generationally distinct samples from the NCDS and Add Health. Data across both samples confirmed that higher intelligence predicted earlier puberty and indicators of slower reproduction over and above several potential confounds, thus constituting a robust validation of our propositions. Findings are discussed with regards to the importance of considering the interplay between obligate and facultative traits, particularly when opposing directions might occur due to evolutionarily novel preferences associated with intelligence, as well as in the context of evolutionary mismatch in modern settings. Future directions inspired by this novel synthesis are offered.
Purpose Uric acid (UA), the end product of purine metabolism, serves as a potent deoxidant of the brain. UA may therefore be related to psychological activities that are culturally endorsed and normatively promoted, insofar as such activities would require high levels of cortical processing, and thus, gradually expose the brain to a greater oxidation risk. We tested this analysis in Japan, a society that values interdependence of the self with others. Methods Middle-aged Japanese adults ( N = 243) were tested twice for the serum UA concentration, with five years in-between. Moreover, an assortment of measures assessing culturally sanctioned traits (those related to interdependence) and culturally non-sanctioned traits (those related to independence) were collected. Results We found that the baseline levels of interdependence predicted an increase in the UA in the next five years. In contrast, there was no such effect for independence. Moreover, the effect of interdependence on the UA increase was mediated by cognitive effort in various domains (such as work, finance, and social relations), suggesting that the culturally sanctioned traits increased cognitive effort devoted to mundane everyday activities, which in turn, predicted the UA to increase over time. Notably, baseline UA levels did not affect changes in psychological traits. Conclusion Interpreting these results in light of UA’s role as a potent antioxidant for brain tissues, we propose that higher UA levels may support metabolically demanding actions aligned with culturally sanctioned practices, particularly those associated with interdependence in the Japanese context.
Social feedback plays a pivotal role in human interactions, significantly impacting psychological and behavioral processes. This study explored the effect of different types of social feedback on neurophysiological function in the context of psychosocial stress and performance. Thirty-nine healthy adults underwent a modified version of the Trier Social Stress Test, in which they prepared and gave five short speeches, each associated with a different social feedback condition: No Feedback, (NoF), Neutral Feedback (NF), Annoyed Feedback (AF), Bored Feedback (BF), and Positive Feedback (PF). Data on electroencephalography (EEG), heart rate (HR), and electrodermal activity (SCL) were collected during the speech preparation phase and following social feedback. HR and SCL were significantly lower in the AF and BF conditions compared to the NoF and NF conditions. Furthermore, EEG data showed higher gamma band activity in the posterior region of interest compared to frontal and central areas; this activity increased from the NoF to the PF, NF, and BF conditions, peaking before declining in the AF condition. Beta band activity was higher in central and posterior regions than in the frontal area and increased from NoF to NF before decreasing in the BF and AF conditions. These results illustrate how social feedback may or may not induce psychosocial stress depending on its valence and identify some potential neurophysiological correlates of adaptive and maladaptive performance under stress.
Purpose:People can judge others' ages from face images somewhat accurately and tend to rateyounger adults' faces as more attractive than older adults' faces. However, individual diff erences inthe strength of this preference for younger adult faces have also been reported, whereby peopleborn to older parents (i.e., people whose parents were older when the participant was born) showedweaker preferences for younger adult faces. However, work showing this pattern of results used facestimuli in which cues of age were experimentally manipulated using computer-graphics methods andmany researchers have recently raised concerns about how well fi ndings obtained using such stimuligeneralise to ratings of natural (i.e., unmanipulated) face images. Methods:In light of the above, we tested whether people born to older parents showed weakerpreferences for younger faces when rating the attractiveness of natural (i.e., unmanipulated) faceimages. Results:Although our analyses demonstrated that participants generally showed strong preferencesfor younger adult faces, the strength of these preferences was not signifi cantly correlated withparental age at birth. Conclusions:Thus, our results do not support the proposal that parental age at birth infl uencespreferences for facial cues of age.
The present study aimed to investigate the extent to which violent intergroup conflict may be associated with human life history trajectories. We examined life histories in a postconflict socioecology (Bosnia and Herzegovina and Kosovo: N = 699) and compared them with a control condition (Serbia: N = 628) using the network analysis approach. Participants from the postconflict environment had higher number of children and reproduction planning, followed by lower age of first reproduction which suggest accelerated life histories. Network analysis showed that fertility and mating-related events in the control ecology were relatively independent from childhood environmental conditions, while fertility itself was positively associated with current socioeconomic status. In contrast, fertility and mating were linked with childhood economic family status and stability of the environment in the postconflict condition; current socioeconomic status was only related to childhood economic status in this network. Short-term mating and the onset of sexual behavior were more strongly positively related to the age of first reproduction in the postconflict socioecology, compared to the control socioecology. Fertility was positively associated with long-term mating and pregnancy planning, and negatively linked with the age of first reproduction in both ecological conditions. Obtained findings are discussed within the theoretical frameworks of fast-slow continuum in life history trajectories and predictive adaptive response hypothesis. The results provide insights into how intergroup conflict may affect human life history dynamics and highlights the fruitfulness of using the network approach to analyze life history trajectories.
