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This study examined neural activity during provocation and aggressive responses among people from different social classes. Participants completed the Point Subtraction Aggression Paradigm while undergoing functional magnetic resonance imaging. Compared to high-class participants, low-class participants behaved more aggressively and exhibited greater activity in the orbitofrontal cortex (OFC) during provocation and greater activity in the insula and striatum during aggressive responses. The relationship between social class and aggression was moderated by OFC and anterior cingulate cortex (ACC) activity to provocation; that is, low-class participants behaved more aggressively than high-class participants when OFC/ACC activity was relatively low. However, this difference was not significant when OFC/ACC activity was higher. Our findings suggest that low-class individuals display higher neural sensitivity during social provocation and aggressive responses than high-class individuals. These results promote future research on the relationship between social class and aggression.

Testosterone (T) fluctuates in response to competitive social interactions, with the direction of change typically depending on factors such as contest outcome. Watching a competition may be sufficient to activate T among fans and others who are invested in the outcome. This study explores the change in T associated with vicarious experiences of competition among combat sport athletes viewing a teammate win or lose and assesses how individual differences in social identification with one’s team relates to these patterns of T reactivity. Twenty-six male combat athletes completed a social identity questionnaire on a neutral day. Later, salivary samples (assayed for T) were obtained before and after athletes viewed a video of a teammate engaged in a formal contest. T reactivity to viewing a teammate compete varied among participants in both the magnitude and direction of change, independent of contest outcome. Individual differences in cognitive centrality, a core feature of social identification, showed a strong positive relationship with T reactivity, particularly if their teammate won. Initial findings suggest that dominance-linked androgen responses associated with watching a teammate win a competition might depend on the belief that team membership is central to one’s own identity. These exploratory results in a small sample of combat athletes should be interpreted with caution. Uncovering the role of social group dynamics in influencing T responses to competition is particularly important in light of the evolutionary history of coalitional combat in humans.

Persisting even when the rewards of continued effort are fading is essential for achieving long-term goals, skills, and good health, alike. Yet, we often quit when things get hard. Here, we tested whether augmenting the feeling of control through external measures increases persistence under such discouraging circumstances. In two laboratory experiments, we first induced illusory control by manipulating the base-rate of positive outcomes and then tested the effect of this elevation of participants’ perceived control upon their persistence under diminishing returns and in a competition against a stronger opponent. Induced illusory control significantly enhanced people’s persistence in both of these motivationally challenging situations. Our findings demonstrate that motivation is dependent upon perceived, rather than objective, control, and reveal that this can be leveraged to counteract quitting behavior when things get hard, for instance in rehabilitation, physical activity interventions, or other training settings. Electronic supplementary material The online version of this article (10.3758/s13423-020-01745-4) contains supplementary material, which is available to authorized users.

Despite global efforts to rapidly distribute COVID-19 vaccines, early estimates suggested that 29–35% of the population were hesitant/unwilling to receive them. Countering such vaccine hesitancy is thus an important priority. Across two sets of online studies (total n = 1584) conducted in the UK before (August–October 2020) and immediately after the first effective vaccine was publicly announced (November 10–19, 2020), brief exposure (

Correction to: Nature Human Behaviour https://doi.org/10.1038/s41562-021-01173-x, published online 2 August 2021.In the version of this article initially published, the following authors were omitted from the author list and the Author contributionssection for “investigation” and “writing and editing”: Nandor Hajdu (Institute of Psychology, ELTE Eötvös Loránd University, Budapest,Hungary), Jordane Boudesseul (Facultad de Psicología, Instituto de Investigación Científica, Universidad de Lima, Lima, Perú), RafałMuda (Faculty of Economics, Maria Curie-Sklodowska University, Lublin, Poland) and Sandersan Onie (Black Dog Institute, UNSWSydney, Sydney, Australia & Emotional Health for All Foundation, Jakarta, Indonesia). In addition, Saeideh FatahModares’ name wasoriginally misspelled as Saiedeh FatahModarres in the author list. Further, affiliations have been corrected for Maria Terskova (NationalResearch University Higher School of Economics, Moscow, Russia), Susana Ruiz Fernandez (FOM University of Applied Sciences,Essen; Leibniz-Institut fur Wissensmedien, Tubingen, and LEAD Research Network, Eberhard Karls University, Tubingen, Germany),Hendrik Godbersen (FOM University of Applied Sciences, Essen, Germany), Gulnaz Anjum (Department of Psychology, Simon FraserUniversity, Burnaby, Canada, and Department of Economics & Social Sciences, Institute of Business Administration, Karachi, Pakistan).

Few studies have experimentally manipulated sleep to study its effect on aggressive behavior. The current study examined how reactive aggression was affected by having sleep restricted to 4-hours on a single night, a level of disruption commonly experienced. Both rested and sleep-restricted participants completed the Point Subtraction Aggression Paradigm (PSAP), a laboratory task in which participants seek to earn points, are provoked by a fictitious opponent stealing their points, and may choose to steal points in response. Logistic mixed-effect models were used to investigate the effect of sleep restriction and the role of sex hormones on the odds of choosing to steal. For men, and women in the luteal phase of the menstrual cycle, sleep restriction did not result in significant changes reactive aggression, although the patterns of aggressive behavior appeared less reactive and retaliatory in nature. For women in the follicular phase of the menstrual cycle, sleep restriction was associated with higher levels of reactive aggression. For both men and women in the luteal phase, sleep restriction disrupted an association between hormone change over the task (testosterone and estradiol, respectively) and reactive aggression that was observed in their control participants. In addition, higher testosterone before the PSAP in men was associated with maintaining a high level of stealing over the task. These results indicate a complex dynamic in which sex hormones and sleep interact to predict aggressive behavior in response to provocation.

Recent research suggests that when we lack a sense of control, we are prone to motivational failures and early quitting in competitions. Testosterone, on the other hand, is thought to boost competitiveness. Here we investigate the interaction between these factors, testing the testosterone's potential to enhance persistence in a competition against a stronger opponent, depending on experimentally manipulated perceived control. Healthy participants were administered a single dose of testosterone or placebo. They first underwent a task designed to either induce low or high perceived control and then entered a costly competition against a progressively stronger opponent that they could quit at any time. In the placebo group, men with low perceived control quitted twice as early as those with high perceived control. Testosterone countered this effect, making individuals with low control persist in the competition for as long as those with high perceived control, and did so also despite raising participants' explicit awareness of the opponents' advantage. This psychoendocrinological effect was not modulated by basal cortisol levels, CAG repeat polymorphism of the androgen receptor gene, or trait dominance. Our results provide the first causal evidence that testosterone promotes competitive persistence in humans and demonstrate that this effect depends on the psychological state elicited prior to the competition, broadening our understanding of the complex relationships between testosterone and social behaviors.

Attractiveness judgements influence desires to initiate and maintain romantic relationships. Testosterone also predicts relationship initiation and maintenance; such effects may be driven by the hormone's modulation of attractiveness judgements, but no studies have investigated causal (and situation-dependent) effects of the hormone on these judgements. Using a placebo-controlled cross-over design, our preregistered analyses revealed order- and relationship- dependent effects: single heterosexual men judged the women as more appealing when testosterone was administered first (and placebo second), but marginally less appealing when placebo was administered first (and testosterone second). In a more complex model incorporating the women's attractiveness (as rated by an independent set of observers), however, we show that testosterone increases the appeal of women -but this effect depends upon the men's relationship status and the women's attractiveness. In partnered men (n = 53) who tend to derogate attractive alternatives (by rating them as less appealing), testosterone countered this effect, boosting the appeal of these attractive alternatives. In single men (n = 53), conversely, testosterone increased the appeal of low-attractive women. These differential effects highlight the possibility of a newly discovered mechanism whereby testosterone promotes male sexual reproduction through different routes depending on relationship status, promoting partner up- rather than down-grading when partnered and reducing choosiness when single. Further, such effects were relatively rapid [within 85 (±5) minutes], suggesting a potential non-genomic mechanism of action.

Testosterone is often considered a critical regulator of aggressive behaviour. There is castration/replacement evidence that testosterone indeed drives aggression in some species, but causal evidence in humans is generally lacking and/or—for the few studies that have pharmacologically manipulated testosterone concentrations—inconsistent. More often researchers have examined differences in baseline testosterone concentrations between groups known to differ in aggressiveness (e.g., violent vs non-violent criminals) or within a given sample using a correlational approach. Nevertheless, testosterone is not static but instead fluctuates in response to cues of challenge in the environment, and these challenge-induced fluctuations may more strongly regulate situation-specific aggressive behaviour. Here, we quantitatively summarize literature from all three approaches (baseline, change, and manipulation), providing the most comprehensive meta-analysis of these testosterone-aggression associations/effects in humans to date. Baseline testosterone shared a weak but significant association with aggression (r = 0.054, 95% CIs [0.028, 0.080]), an effect that was stronger and significant in men (r = 0.071, 95% CIs [0.041, 0.101]), but not women (r = 0.002, 95% CIs [−0.041, 0.044]). Changes in T were positively correlated with aggression (r = 0.108, 95% CIs [0.041, 0.174]), an effect that was also stronger and significant in men (r = 0.162, 95% CIs [0.076, 0.246]), but not women (r = 0.010, 95% CIs [−0.090, 0.109]). The causal effects of testosterone on human aggression were weaker yet, and not statistically significant (r = 0.046, 95% CIs [−0.015, 0.108]). We discuss the multiple moderators identified here (e.g., offender status of samples, sex) and elsewhere that may explain these generally weak effects. We also offer suggestions regarding methodology and sample sizes to best capture these associations in future work.

Unlike for men, cues of threat in women's faces have not been well-studied. Although morphological markers, such as facial width-to-height ratio (fWHR) and body mass index (BMI), have been associated with physical threat in men, evidence for these relationships in women is less clear. Further, because women's aggression is typically social rather than physical, it is possible that threat advertisement and assessment mechanisms evolved to track social rather than physical threat in women and thus involve different cues. This possibility has not been readily investigated. Here we present the results of a study involving more than 36,000 judgements of 98 women's faces from 635 independent raters on 12 different threat-related characteristics—one of the most comprehensive analysis of perceptions of threat in women's faces to date. Perceptions of threat/influence in women's faces were related to their actual social but not physical threat. Further, fWHR and BMI did not appear to account for this accuracy. Our results suggest that threat advertisement and assessment in women may track their propensity to socially rather than physically harm others.

Victimized women are thought to have impairments in identifying risk and to have dysfunctional reactions to threatening situations, which increase the risk for revictimization. To investigate possible deficits in revictimized women, we used a method examining women's perceptions of an implicit facial cue of aggressiveness – the facial Width-to-Height Ratio (fWHR). We tested whether revictimized women show impairments in detecting aggressiveness in male faces by neglecting cues of fWHR and choosing a smaller preferred distance to men. Fifty-two revictimized PTSD patients and 52 healthy controls provided ratings of aggressiveness and attractiveness for 65 photographed men and chose their preferred distance towards 11 pictured men. Multiple regression analyses indicated that revictimized women do not show impairments in perceiving and reacting to cues of aggression accurately. Hierarchical linear models, however, indicated that revictimized women rated all men as less aggressive. Revictimized women with histories of intimate partner violence (IPV) rated men with larger fWHRs and higher values of actual aggression to be more attractive than did revictimized women without IPV histories. A reduced appraisal of threat signals as threatening and an attraction to wider-faced and more aggressive men might increase the risk for revictimization.

Individuals with larger facial width-to-height ratios (FWHRs) are judged as more threatening, and engage in more threat-related behavior, than do individuals with smaller FWHRs. Here we identified components of threat potential that are related to the FWHR. In Study 1, the FWHR was correlated positively with physical threat potential (bicep size) in women and with both physical and psychological (anger proneness) threat potential in men. Behavioral aggression was measured in a subset of these participants using the Point Subtraction Aggression Paradigm (costly aggression) and a Money Allocation Task (non-costly aggression). Psychological (but not physical) threat potential predicted non-costly aggression and physical (but not psychological) threat potential predicted costly aggression. In Study 2, a separate set of participants judged the anger proneness, strength, or aggressiveness of male participants photographed in Study 1. Participants' judgements of all three characteristics were associated with the FWHR, and there were sex differences in how aggressiveness was conceptualized (for women, aggressiveness was associated with anger proneness, for men, aggressiveness was associated with strength). These results are consistent with the hypothesis that the FWHR may be an adaptation to cue the threat potential of men.

The central aim of this study was to investigate hormones as a predictor of individual vulnerability or resiliency on emotion processing tasks following one night of sleep restriction. The restriction group was instructed to sleep 3 a.m.–7 a.m. (13 men, 13 women in follicular phase, 10 women in luteal phase of menstrual cycle), and a control group slept 11 p.m.–7 a.m. (12 men, 12 follicular women, 12 luteal women). Sleep from home was verified with actigraphy. Saliva samples were collected on the evening prior to restriction, and in the morning and afternoon following restriction, to measure testosterone, estradiol, and progesterone. In the laboratory, event-related potentials (ERPs) were recorded during presentation of images and faces to index neural processing of emotional stimuli. Compared to controls, sleep-restricted participants had a larger amplitude Late Positive Potential (LPP) ERP to positive vs neutral images, reflecting greater motivated attention towards positive stimuli. Sleep-restricted participants were also less accurate categorizing sad faces and exhibited a larger N170 to sad faces, reflecting greater neural reactivity. Sleep-restricted luteal women were less accurate categorizing all images compared to control luteal women, and progesterone was related to several outcomes. Morning testosterone in men was lower in the sleep-restricted group compared to controls; lower testosterone was associated with lower accuracy to positive images, a greater difference between positive vs neutral LPP amplitude, and lower accuracy to sad and fearful faces. In summary, women higher in progesterone and men lower in testosterone were more vulnerable to the effects of sleep restriction on emotion processing tasks. This study highlights a role for sex and sex hormones in understanding individual differences in vulnerability to sleep loss., Highlights • Sex and sex hormones play a role in individual differences in vulnerability to sleep loss. • Women higher in progesterone and men lower in testosterone were more vulnerable to the effects of sleep restriction on emotion processing tasks. • One night of sleep restriction was associated with lower testosterone in men. • Sleep-restricted participants showed greater motivated attention towards positive picture stimuli compared to rested controls. • Sleep-restricted participants were less accurate categorizing sad faces and exhibited a larger N170 ERP to sad faces, reflecting greater neural reactivity.

Recent research on testosterone and risk-taking behavior is beginning to focus on the role of context-dependent changes in testosterone. Extending this research, our study investigated the association between testosterone reactivity to competitive outcomes and risk-taking in the context of a video game based competition. The study also examined whether self-construal moderated this relationship. Results indicated that a rise in testosterone during competition did not predict subsequent risk-taking behavior. However, a rise in testosterone during competition predicted subsequent risk-taking behaviors within winners with independent self-construals. Nevertheless, results did not reveal an association between basal testosterone and risk-taking, nor did competitive outcomes modulate a differential testosterone response. Overall, we treat these findings as preliminary, as there were multiple analyses conducted and effect sizes were relatively small. We discuss these results in the context of recent animal findings that testosterone facilitates success at future competitions after winning a competition, as well as recent research suggesting self-construal moderates associations between testosterone and aggression.

Previous research indicates that men’s testosterone levels, or personality and contextual variables known to influence testosterone levels, predict men’s attributions of social and personality characteristics from faces. However, the correlational nature of many of these past findings precludes our ability to establish causal pathways. Here, across two pharmacological challenge experiments, we examined the extent to which testosterone reduced men’s perceptions of trustworthiness from emotionally-neutral faces (Experiment 1, N = 30, within-subjects design) or sensitivity to dominance from men’s faces that varied in characteristically dominant shape (Experiment 2, N = 117, between-subjects design). Results from Experiment 1 showed that administration of testosterone did not significantly lower men’s perceptions of trustworthiness. An unexpected order effect (i.e., drug x order of administration interaction) showed that trustworthiness ratings were higher after testosterone, but only if men received testosterone on the first day and placebo on the second day; importantly, this effect was directionally opposite to that reported in the literature and to that predicted for the present study. Experiment 2 demonstrated that dominance perceptions did not vary as a function of whether men received testosterone or placebo. Supplementary analyses with linear mixed effects generally support the main findings across experiments, but also provide more nuanced details involving exploratory individual difference variables. Results from the present experiments provide important information to a growing body of research examining testosterone and complex social processes, and may help inform future research on the topic.

Costly punishment is thought to have evolved because it promotes cooperation and the equitable sharing of resources, but the costs associated with punishment – for both the punisher and the punished – limit the efficiency of this enforcement system in economic interactions. Reputation may also guide decision-making, but this information is not always available (e.g., in interactions involving strangers). Across several bargaining studies, we provide evidence of an efficient and flexible "threat-based" bargaining system that can influence the division of resources without the need for costly punishment and reputational information. We found that participants, without prompting, dynamically adjusted bargaining based on the perceived threat-potential (resource holding power and aggressiveness) of the bargaining partner, giving larger offers to individuals who appeared more threatening. These effects of perceived threat-potential were strongest among participants who were most vulnerable to harm in physical contests (women vs men and weaker men vs stronger men), despite that offers were made on-line and anonymously to photographs of the individuals rather than in face-to-face interactions. These results may reflect an overgeneralization of a real-world threat heuristic that allows low threat individuals to extract resources when possible, while avoiding physical retaliation and harm, and high threat individuals to appropriate larger shares of a resource through static facial cues of threat rather than by physically expressing their propensity to punish. Previously, researchers have highlighted the monetary advantages of attractiveness (the "beauty premium"), but the effects of threat either trumped, devalued, or were equivalent to those of attractiveness.

Background Although traditional wisdom suggests that baseline levels of testosterone (T) promote aggressive behavior, decades of research have produced findings that have been largely weak and inconsistent. However, more recent experimental work suggests that exogenous administration of T rapidly potentiates amygdala and hypothalamus responses to angry facial expressions. Notably, these brain regions are rich in androgen receptors and play a key role in modulating aggressive behavior in animal models. Methods The present experiment extends this work by examining whether acutely increasing T potentiates aggressive behavior in men. In a double-blind, placebo-controlled, between-subject design, healthy adult men ( n = 121) were administered either T or placebo, and subsequently engaged in a well-validated decision-making game that measures aggressive behavior in response to social provocation. In light of prior correlational research, we also assessed the extent to which T's effects on aggressive behavior would depend on variability in trait dominance and/or trait self-control. Results Exogenous T on its own did not modulate aggressive behavior. However, T's effects on aggression were strongly influenced by variation in trait dominance and trait self-control. Specifically, T caused an increase in aggressive behavior, but only among men scoring relatively high in trait dominance or low in trait self-control. Conclusions These findings are the first to demonstrate that T can rapidly (within 60 minutes) potentiate aggressive behavior, but only among men with dominant or impulsive personality styles.

A contribution to a special issue on Hormones and Human Competition.The ease of measuring steroids in saliva has led to an increase in investigating their role in competition and aggression in laboratory settings and using behavioral measures of aggression. We review here the Point-Subtraction-Aggression-Paradigm (PSAP) as a measure of costly aggression and we compare and contrast the PSAP to other aggression measures. We describe our use of the PSAP, highlighting how it can be modified to investigate a broad array of experimental questions. We review studies that have investigated neuroendocrine function and the PSAP, and we conclude that across studies the relationship between fluctuations in testosterone and PSAP aggression scores are directionally positive, and are likely specific to men. Investigations of other neuroendocrine measures and the PSAP are fewer, limiting conclusions that can be drawn for other hormones. We provide two versions of the PSAP that can be used with E-PRIME® software for researchers interested in this measure for their laboratories.

Facial width-to-height ratio (fWHR) is correlated with a number of aspects of aggressive behavior in men. Observers appear to be able to assess aggressiveness from male fWHR, but implications for interpersonal distance preferences have not yet been determined. This study utilized a novel computerized stop-distance task to examine interpersonal space preferences of female participants who envisioned being approached by a man; men's faces photographed posed in neutral facial expressions were shown in increasing size to mimic approach. We explored the effect of the men's fWHR, their behavioral aggression (measured previously in a computer game), and women's ratings of the men's aggressiveness, attractiveness, and masculinity on the preferred interpersonal distance of 52 German women. Hierarchical linear modelling confirmed the relationship between the fWHR and trait judgements (ratings of aggressiveness, attractiveness, and masculinity). There were effects of fWHR and actual aggression on the preferred interpersonal distance, even when controlling statistically for men's and the participants' age. Ratings of attractiveness, however, was the most influential variable predicting preferred interpersonal distance. Our results extend earlier findings on fWHR as a cue of aggressiveness in men by demonstrating implications for social interaction. In conclusion, women are able to accurately detect aggressiveness in emotionally neutral facial expressions, and adapt their social distance preferences accordingly.

Hierarchy, the relative ranking of individuals with respect to status or other social dimensions, is ubiquitous across human social groups. However, relatively little is known about the biological factors that may promote or inhibit mobility in status hierarchies. Prominent theoretic perspectives suggest that concentrations of testosterone in the bloodstream fluctuate dynamically in anticipation of and in response to social challenges, serving to promote behaviors aimed at gaining/maintaining status. This chapter reviews studies that have directly examined the extent to which endogenous, competition-induced surges in testosterone predicted subsequent competitiveness and aggressiveness. Studies suggest that testosterone surges promote competitiveness, but that this effect is complex and depends on several factors. More consistent was evidence that testosterone surges predicted subsequent aggressive behavior. Testosterone–behavior links were also specific to men, suggesting that surges in this hormone may serve different functions, or may promote alternative behavioral strategies for gaining and maintaining status, in women.

Little is known about the neurobiological pathways through which testosterone promotes aggression or about the people in whom this effect is observed. Using a psychopharmacogenetic approach, we found that testosterone increases aggression in men ( N = 308) with select personality profiles and that these effects are further enhanced among those with fewer cytosine-adenine-guanine (CAG) repeats in exon 1 of the androgen receptor (AR) gene, a polymorphism associated with increased AR efficiency. Testosterone’s effects were rapid (~30 min after administration) and mediated, in part, by subjective reward associated with aggression. Testosterone thus appears to promote human aggression through an AR-related mechanism and to have stronger effects in men with the select personality profiles because it more strongly upregulates the subjective pleasure they derive from aggression. Given other evidence that testosterone regulates reward through dopaminergic pathways, and that the sensitivity of such pathways is enhanced among individuals with the personality profiles we identified, our findings may also implicate dopaminergic processes in testosterone’s heterogeneous effects on aggression.

Variation in the facial width-to-height ratio (fWHR) maps onto a number of behavioral and psychological traits among men (e.g., aggression, unethical behavior, negotiation performance). Importantly, observer judgments of many of these traits also correlate strongly with the fWHR, suggesting that it may represent an honest cue to dominance and status. It has been speculated that the relationship between fWHR and these behavioral traits is due to pubertal testosterone concurrently shaping facial structure and traits linked to social dominance. Others, however, have provided some initial, although inconsistent, evidence that circulating testosterone levels in adulthood may underlie associations between the fWHR and behavioral displays. Here, we provide a more powerful test of the second model by examining the relationship between fWHR, baseline testosterone, and competition-induced testosterone reactivity, across seven diverse samples of men (total N= 780). We also report a further analysis including data published previously, for a total sample of 1041 men. Analysis of our individual samples, in addition to an internal meta-analysis, demonstrated no significant positive relationship between fWHR and baseline testosterone, or fWHR and three measures of competition-induced testosterone reactivity. We discuss potential reasons for previous discrepancies, and suggest avenues for future research.

The social heuristic hypothesis posits that human cooperation is an intuitive response that is expressed especially under conditions of time-constraint. Conversely, it proposes that for individuals given an opportunity for reflection, cooperation is more likely to be curtailed by an optimizing process calibrated to maximize individual benefit in a given situation. Notably, the steroid hormone testosterone has also been implicated in intuitive decision-making, including both prosocial and anti-social behaviors, with effects strongest in men with particular dispositional characteristics. This raises the possibility that increased testosterone may augment the effects predicted by the social heuristic hypothesis, particularly among men higher in specific dispositional characteristics (dominance, impulsivity, independent self-construal: high risk for testosterone-induced antisocial behavior). Here, in a testosterone administration study with a relatively large sample of men (N = 400), we test this possibility in a double-blind, placebo-controlled paradigm, with men randomly assigned to play a one-shot public goods game either under time-pressure (forced intuition) or with a time delay (forced reflection). Results revealed that within the placebo group, time-pressure (versus forced delay) increased cooperation among low risk men, but decreased cooperation among high risk men. Testosterone further moderated this pattern by abolishing the time-pressure effect in low risk men and—in high risk men—reversing the effect by selectively reducing offers (compared to placebo) under forced delay. This is the first evidence that testosterone and personality can interact with time-pressure and delay to predict human cooperation.

Contribution to Special Issue on Fast effects of steroids. It is well documented that testosterone concentrations change rapidly within reproductively relevant contexts (e.g., competition, mate-seeking). It has been argued that such rapid changes in testosterone may serve to adaptively fine-tune ongoing and/or future social behaviour according to one's social environment. In this paper, we review human correlational and experimental evidence suggesting that testosterone fluctuates rapidly in response to competition and mate-seeking cues, and that such acute changes may serve to modulate ongoing and/or future social behaviours (e.g., risk-taking, competitiveness, mate-seeking, and aggression). Some methodological details, which limit interpretation of some of this human work, are also discussed. We conclude with a new integrative model of testosterone secretion and behaviour, the Fitness Model of Testosterone Dynamics. Although we focus primarily on human aggression in this review, we also highlight research on risk-taking, competitiveness, and mate-seeking behaviour.

Snap judgements of threat based on exposure to the human face were likely maintained throughout history because they facilitated survival when encountering strangers. If an evolved adaptation, then such judgements should rely on static facial cues that are not masked by facial hair, as may have been the case for our ancestors. We show that the facial width-to-height ratio (FWHR) is not obscured by facial hair and that it reliably and consistently cues observers' (n=56) judgements of aggression, but not of masculinity, in bearded ( r =.59) and in non-bearded ( r =.66) versions of the same male faces. The high reliability of the FWHR irrespective of facial hair and the evidence that judgements of threat based on the FWHR have some accuracy, suggests our perceptual system may have evolved to be sensitive to the FWHR along with the perceptual bias to extract information preferentially from the upper-face.

What motivates people to act against their own self-interest? In men, what seems to be irrational decision-making in the short-term may be explained by other long-term benefits; thus retaliation may not be motivated by tangible costs, but instead intangible psychological variables (e.g., status threats). In contrast, there is evidence that women are more sensitive to tangible costs than are men. In Experiment 1, using the Point Subtraction Aggression Paradigm (PSAP), we tested the prediction that in men, the frequency of provocation, and not the monetary loss (tangible cost), would be associated with retaliation, whereas women would be sensitive to the tangible costs. In keeping with the prediction, women (n = 80) who incurred greater tangible costs (irrespective of frequency) retaliated with more costly punishment, whereas men (n = 90) who were provoked more frequently (irrespective of tangible costs) retaliated with more costly punishment. In Experiment 2, we directly investigated whether women were more sensitive to threats to resources and men were more sensitive to threats to status, as suggested by the results of Experiment 1. Women's (n = 53) retaliation was greater when they reported it to be a means to protect their resources, and men's (n = 35) retaliation was greater when they reported it to be a means to protect their status. Thus, these results identify psychological variables that guide retaliation that is costly to the actor. Consistent with evolutionary perspectives, concerns about status appear to drive costly retaliatory behavior more so in men than in women.

The facial width-to-height ratio (fWHR) is associated with a range of behaviours in men, but little is known about the underlying psychological mechanisms. We tested whether psychopathic personality traits were related to fWHR and mediated the link between this metric and cheating behaviour. Participants (146 men, 76 women) completed the Psychopathic Personality Inventory-Revised and rolled dice to determine the number of ballots allowed for entry into a lottery for a cash prize. Men’s willingness to cheat (entering more ballots than permitted) and their extent of cheating (number of additional ballots) was associated positively with fearless dominance and fWHR. Further, in men, fearless dominance was correlated with fWHR and mediated the relationship between fWHR and willingness to cheat, but not the extent of cheating. In women, there were no differences in fWHR or in personality traits between cheaters and non-cheaters. Psychopathic personality traits may thus underlie some fWHR-behaviour relationships in men.

Like other animals, humans are sensitive to facial cues of threat. Recent evidence suggests that we use this information to dynamically calibrate competitive decision-making over resources, ceding more to high-threat individuals (who appear more willing/able to retaliate) and keeping more from low-threat individuals. Little is known, however, about the biological factors that support such threat assessment and decision-making systems. In a pre-registered, double-blind, placebo-controlled, cross-over testosterone administration study ( n = 118 men), we show for the first time that testosterone reduces the effects of threat on decision-making: participants ceded more resources to high-threat (versus low-threat) individuals (replicating the ‘threat premium’), but this effect was blunted by testosterone, which selectively reduced the amount of resources ceded to those highest in threat. Thus, our findings suggest that testosterone influences competitive decision-making by recalibrating the integration of threat into the decision-making process.

Few studies have investigated the influence of changes in testosterone on subsequent competitive, antagonistic behavior in humans. Further, little is known about the extent to which such effects are moderated by personality traits. Here, we collected salivary measures of testosterone before and after a rigged competition. After the competition, participants were given the opportunity to act antagonistically against the competitor (allocate a low honorarium). We hypothesized that changes in testosterone throughout the competition would predict antagonistic behavior such that greater increases would be associated with the allocation of lower honorariums. Further, we investigated the extent to which personality traits related to psychopathy (fearless dominance, FD; self-centered impulsivity, SCI; and coldheartedness) moderated this relationship. In men (n=104), greater increases in testosterone and greater FD were associated with more antagonistic behavior, but testosterone concentrations did not interact with personality measures. In women (n=97), greater FD and SCI predicted greater antagonistic behavior, but there were no significant endocrine predictors or interactions with personality measures. In a secondary set of analyses, we found no support for the dual-hormone hypothesis that the relationship between baseline testosterone concentrations and behavior is moderated by cortisol concentrations. Thus, results are consistent with previous findings that in men, situation-specific testosterone reactivity rather than baseline endocrine function is a better predictor of future antagonistic behavior. The results are discussed with respect to the Challenge Hypothesis and the Biosocial Model of Status, and the possible mechanisms underlying the independent relations of testosterone and personality factors with antagonistic behavior.

A contribution to a special issue on Hormones and Human Competition. Since Archer's (2006) influential meta-analysis, there has been a major increase in the number of studies investigating the effect of competition outcome on testosterone reactivity patterns in humans. Despite this increased research output, there remains debate as to whether competition outcome modulates testosterone concentrations. The present paper examines this question using a meta-analytic approach including papers published over the last 35years. Moreover, it provides the first meta-analytic estimate of the effect of competition outcome on testosterone concentrations in women. Results from a meta-analysis involving 60 effect sizes and >2500 participants indicated that winners of a competition demonstrated a larger increase in testosterone concentrations relative to losers (D=0.20)-an effect that was highly heterogeneous. This 'winner-loser' effect was most robust in studies conducted outside the lab (e.g., in sport venues) (D=0.43); for studies conducted in the lab, the effect of competition outcome on testosterone reactivity patterns was relatively weak (D=0.08), and only found in studies of men (D=0.15; in women: D=-0.04). Further, the 'winner-loser' effect was stronger among studies in which pre-competition testosterone was sampled earlier than (D=0.38, after trim and fill correction) rather than within (D=0.09) 10min of the start of the competition. Therefore, these results also provide important insight regarding study design and methodology, and will be a valuable resource for researchers conducting subsequent studies on the 'winner loser' effect.

The facial width-to-height ratio (FWHR) is the width of the face divided by the height of the upper face. There is mixed evidence for the hypothesis that the FWHR is a cue of threat and dominance in the human face. We conducted a systematic review and meta-analyses of all peer-reviewed studies (and 2 unpublished studies) to estimate the magnitude of the sex difference in the FWHR, and the magnitude of the relationship between the FWHR and threatening and dominant behaviours and perceptions. Studies were eligible for inclusion if the authors reported an analysis involving the FWHR. Our analyses revealed that the FWHR was larger in men than in women (d¯ = .11, n = 10,853), cued judgements of masculinity in men (r¯ = .35, n of faces = 487; n of observers = 339), and was related to body mass index (r¯ = .31, n = 2,506). Further, the FWHR predicted both threat behaviour in men (r¯ = .16, n = 4,603) and dominance behaviour in both sexes (r¯ = .12, n = 948) across a variety of indices. Individuals with larger FWHRs were judged by observers as more threatening (r¯ = .46, n of faces = 1,691; n of observers = 2,076) and more dominant (r¯ = .20, n of faces = 603; n of observers = 236) than those with smaller FWHRs. Individuals with larger FWHRs were also judged as less attractive (r¯ = -.26, n of faces = 721; n of observers = 335), especially when women made the judgements. These findings provide some support for the hypothesis that the FWHR is part of an evolved cueing system of intra-sexual threat and dominance in men. A limitation of the meta-analyses on perceptions of threat and dominance were the low number of stimuli involving female and older adult faces.

What motivates people to act against their own self-interest? In men, what seems to be irrational decision-making in the short-term may be explained by other long-term benefits; thus retaliation may not be motivated by tangible costs, but instead intangible psychological variables (e.g., status threats). In contrast, there is evidence that women are more sensitive to tangible costs than are men. In Experiment 1, using the Point Subtraction Aggression Paradigm (PSAP), we tested the prediction that in men, the frequency of provocation, and not the monetary loss (tangible cost), would be associated with retaliation, whereas women would be sensitive to the tangible costs. In keeping with the prediction, women (n = 80) who incurred greater tangible costs (irrespective of frequency) retaliated with more costly punishment, whereas men (n = 90) who were provoked more frequently (irrespective of tangible costs) retaliated with more costly punishment. In Experiment 2, we directly investigated whether women were more sensitive to threats to resources and men were more sensitive to threats to status, as suggested by the results of Experiment 1. Women's (n = 53) retaliation was greater when they reported it to be a means to protect their resources, and men's (n = 35) retaliation was greater when they reported it to be a means to protect their status. Thus, these results identify psychological variables that guide retaliation that is costly to the actor. Consistent with evolutionary perspectives, concerns about status appear to drive costly retaliatory behavior more so in men than in women.

Variation in the facial width-to-height ratio (face ratio) is associated with judgments of aggression and of trustworthiness made by observers when viewing men's faces. Although judgments of aggression and of trustworthiness are correlated, they represent distinct constructs. We thus investigated the hypothesis that judgments of aggression share stronger associations with the face ratio than judgments of trustworthiness, and that judgments of aggression mediate the link between the face ratio and trustworthiness. Across 4 separate studies, involving 129 observers rating subsets of 141 photographs (original photographs of individuals who provided consent for their use) of clean-shaven (65 faces), unshaved (22 faces), or digitized male faces (54 faces; digitized faces were creating using facial modeling software), this hypothesis was supported. The correlations between the face ratio and judgments of aggression were moderate to strong in all 4 studies (rs =.45 to.70). Reaction time was measured in Study 4: Participants judged aggression faster than trustworthiness; thus, temporal precedence also supports the hypothesis that aggression mediates the link between the face ratio and trustworthiness. Sensitivity to the face ratio may therefore be part of a perceptual mechanism specialized to assess aggressiveness rather than trustworthiness in others, likely because of the greater necessity for rapid judgments of aggressive potential than trustworthiness. (PsycINFO Database Record (c) 2014 APA, all rights reserved). Language: en

Biological models have typically framed sexual orientation in terms of effects of variation in fetal androgen signaling on sexual differentiation, although other biological models exist. Despite marked sex differences in facial structure, the relationship between sexual orientation and facial structure is understudied. A total of 52 lesbian women, 134 heterosexual women, 77 gay men, and 127 heterosexual men were recruited at a Canadian campus and various Canadian Pride and sexuality events. We found that facial structure differed depending on sexual orientation; substantial variation in sexual orientation was predicted using facial metrics computed by a facial modelling program from photographs of White faces. At the univariate level, lesbian and heterosexual women differed in 17 facial features (out of 63) and four were unique multivariate predictors in logistic regression. Gay and heterosexual men differed in 11 facial features at the univariate level, of which three were unique multivariate predictors. Some, but not all, of the facial metrics differed between the sexes. Lesbian women had noses that were more turned up (also more turned up in heterosexual men), mouths that were more puckered, smaller foreheads, and marginally more masculine face shapes (also in heterosexual men) than heterosexual women. Gay men had more convex cheeks, shorter noses (also in heterosexual women), and foreheads that were more tilted back relative to heterosexual men. Principal components analysis and discriminant functions analysis generally corroborated these results. The mechanisms underlying variation in craniofacial structure--both related and unrelated to sexual differentiation--may thus be important in understanding the development of sexual orientation.

Women's preferences for masculine-looking male faces are inconsistent across studies, with some studies finding a positive relationship between masculinity and attractiveness and others finding a negative relationship or no association. One possible reason for this inconsistency is that the perception of masculinity is also associated with perceptions of aggression, which may be viewed as particularly costly to women (aggressive individuals are more likely to experience injury or death). Based on the proposal that women's preference for masculinity is in conflict with their aversion for aggression in male faces, we hypothesized that the bivariate associations between perceptions of masculinity and attractiveness would be weak or negative, but would be positive and significantly stronger after controlling statistically for perceptions of aggression. Across three studies involving three sets of faces ( n = 25, 54, 24) and five sets of raters ( n = 29, 30, 26, 16, 10), this hypothesis was supported with the average correlation between perceptions of masculinity and attractiveness ( r = −.09) reversing in direction and substantially increasing in magnitude after perceptions of aggression were controlled statistically ( r = .35). Perceived masculinity may thus involve both attractive and unattractive components, and women's preferences for masculinity may involve weighing its relative costs and benefits.

The role of sleep deprivation in aggressive behavior has not been systematically investigated, despite a great deal of evidence to suggest a relationship. We investigated the impact of 33 h of sleep loss on endocrine function and reactive aggression using the Point Subtraction Aggression Paradigm (PSAP) task. PSAP performance was assessed in 24 young men and 25 women who were randomly assigned to a sleep deprivation or control condition. Sleep deprivation lowered reactive aggression and testosterone (but not cortisol) in men, and disrupted the positive relationship between a pre-post PSAP increase in testosterone and aggression that was evident in rested control men. While women increased aggression following provocation as expected, no influence of sleep deprivation was found. This is the first experimental study to demonstrate that sleep deprivation lowers reactive aggression in men. Testosterone, but not cortisol, played a role in the relationship between sleep and reactive aggression in men.

The facial width-to-height ratio (face ratio), is a sexually dimorphic metric associated with actual aggression in men and with observers' judgements of aggression in male faces. Here, we sought to determine if observers' judgements of aggression were associated with the face ratio in female faces. In three studies, participants rated photographs of female and male faces on aggression, femininity, masculinity, attractiveness, and nurturing. In Studies 1 and 2, for female and male faces, judgements of aggression were associated with the face ratio even when other cues in the face related to masculinity were controlled statistically. Nevertheless, correlations between the face ratio and judgements of aggression were smaller for female than for male faces (F(1,36) = 7.43, p = 0.01). In Study 1, there was no significant relationship between judgements of femininity and of aggression in female faces. In Study 2, the association between judgements of masculinity and aggression was weaker in female faces than for male faces in Study 1. The weaker association in female faces may be because aggression and masculinity are stereotypically male traits. Thus, in Study 3, observers rated faces on nurturing (a stereotypically female trait) and on femininity. Judgements of nurturing were associated with femininity (positively) and masculinity (negatively) ratings in both female and male faces. In summary, the perception of aggression differs in female versus male faces. The sex difference was not simply because aggression is a gendered construct; the relationships between masculinity/femininity and nurturing were similar for male and female faces even though nurturing is also a gendered construct. Masculinity and femininity ratings are not associated with aggression ratings nor with the face ratio for female faces. In contrast, all four variables are highly inter-correlated in male faces, likely because these cues in male faces serve as "honest signals".

Social exclusion increases aggressive behaviour, and the possible neuroendocrine underpinnings of the effect are largely unknown. Here, we examined the extent to which testosterone and cortisol responses to social exclusion would predict subsequent reactive aggression. Men were randomly assigned to a social exclusion (SE) or inclusion (SI) condition of ‘Cyberball’, a computer ball-toss game. Aggression was then measured using the Point Subtraction Aggression Paradigm (PSAP). Saliva was collected at three points for the measurement of testosterone and cortisol. Regression analyses indicated that testosterone concentrations 10-min into the PSAP (controlling for pre- and post-Cyberball testosterone) were positively correlated with aggressive behaviour, irrespective of SI/SE. Post hoc analyses for the conditions separately, however, suggested the relationship was stronger for SI men ( R 2 change = 13.3%, F 1, 29 = 5.28, p = 0.03) than for SE men ( R 2 change = 1.8%, F 1, 26 = 0.49, p = 0.49). Aggressive behaviour was also positively correlated with cortisol concentrations 10-min into the PSAP (controlling for pre- and post-Cyberball cortisol) irrespective of SE/SI. When both hormones were included in the regression model, the interaction of baseline ‘Cortisol’ × ‘Testosterone’ × ‘Experimental Group’ approached significance ( R 2 change = 5.4%, F 1, 55 = 3.53, p = 0.07), but no significant effects were observed in either group alone. The findings add to evidence that individual differences in state neuroendocrine function map onto variability in human social behaviour.