Adaptive Human Behavior and Physiology最新文献

Purpose

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.

Methods

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.

Results

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.

Conclusion

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.

Purpose

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.

Methods

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.

Results

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.

Conclusion

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.

Background

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.

Methods

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.

Results

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.

Conclusions

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.

Purpose

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.

Methods

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

Results indicate no significant associations between eyelash morphology and any of the measures of underlying health and immunocompetence.

Conclusion

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.

Purpose

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.

Methods

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.

Results

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.

Conclusion

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.

Purpose

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.

Methods

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.

Results

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).

Conclusion

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.