Data on donation behavior towards the conservation of migratory species

The data contains 716 individual decisions and responses from a lab-in-field experiment and an exit questionnaire that were conducted in Denmark, Spain, and Ghana. Individuals were initially asked to perform a small effort task (i.e., correctly counting the number of 1's and 0's in a page) to earn money and subsequently asked how much of their earnings they were willing to donate to BirdLife International to conserve Danish, Spanish, and Ghanaian habitats of the Montagu's Harrier, a migratory bird. The data is useful in understanding individual willingness-to-pay to conserve the habitats of the Montagu's Harrier along its flyway and could aid policymakers in having a clearer and more complete idea of support for international conservation. Among other things, the data can be used to look at the effect of individual socio-demographic characteristics and environmental and donation preferences on actual donation behavior.

Typical diet and type of economy do not predict food-sharing behaviors in three Tanzanian societies

Food sharing behavior is a widely observed phenomenon, and it draws attention of scholars interested in finding both proximate and ultimate explanations of such practices. In the current study, we focused on possible socio-economic and environmental food-sharing predictors: type of economy (i.e., immediate-return vs. delayed-return) and typical diet composition (i.e., proportion of proteins and carbohydrates in typical daily caloric intake). We investigated whether members of three societies from Tanzania (N = 177), namely hunter-gatherers (Hadza), pastoralists (Datoga), and agriculturalists (Iraqw) differ with regard to food-sharing patterns in the Dictator Game and reactions to violations of the food-sharing norms in the Ultimatum Game. We found that neither the type of economy nor the typical diet influenced our outcomes. The results indicated, however, that food sharing behavior was positively predicted by certain individual-level characteristics: people of higher strength and lower body fat shared more food, and women were more willing to share food than men.

Hearing Prosocial Stories Increases Hadza Hunter-Gatherers' Generosity in an Economic Game

Folk stories featuring prosocial content are ubiquitous across cultures. One explanation for the ubiquity of such stories is that stories teach people about the local socioecology, including norms of prosociality, and stories featuring prosocial content may increase generosity in listeners. We tested this hypothesis in a sample of 185 Hadza hunter-gatherers. We read participants a story in which the main character either swims with another person (control story) or rescues him from drowning (prosocial story). After hearing the story, participants played a dictator game with dried meat sticks and then were given a recall test of facts presented in the story. There was moderate evidence for a small effect of the prosocial story: participants who heard the prosocial story gave an estimated 0.22 [90% HDI: -0.12-0.57] more meat sticks than those who heard the control story. However, the association between generosity and sex, marital status, and region of residence was stronger; men gave more than women, unmarried participants gave more than married participants, and participants living in a region with more exposure to markets gave more than participants living further from markets. There was no evidence that the prosocial story was more easily recalled than the control story. These results provide some support for the hypothesis that prosocial stories can increase prosociality in listeners, though the effect of hearing a single story is small.

Paranoid thinking and perceived competitive intention

Paranoid thinking, that others are hostile, can be seen even in the general population. Paranoia is considered the expectation that others are competitors who aim to maximize the differences in payoffs rather than maximize their own payoffs. This study examined whether paranoia reflects the irrational belief that others have a competitive intention and is associated with avoiding perceived competition. We recruited 884 US residents via the Internet and conducted a modified Dictator Game, in which monetary allocation was carried out between the Dictator and the Recipient. The Dictator chooses either fair or competitive allocation while selecting the competitive allocation is irrelevant to increasing the Dictator's payoffs. The Recipient decides whether to accept the Dictator's decision or receive sure but low rewards. We found that Recipients with high-level paranoid thinking expected their opponent to select competitive allocation more than those with low levels, even when selecting it was costly for Dictators. Paranoid thinking was not associated with selecting sure rewards or competitive allocations. The results suggest that paranoia reflects the belief that others have a competitive intention but is not related to avoidance behavior against perceived threats and unilateral attacks.

Maladaptive personality traits as predictors of prosocial and trusting behavior in two economic games

BACKGROUND

Dimensional models of personality disorders postulate interpersonal dysfunction as the core feature of personality pathology, and describe maladaptive personality traits that characterize the specific pattern of dysfunction that is experienced. Herein, we examined whether maladaptive traits predict prosocial and trusting behavior, both of which are highly relevant behaviors for interpersonal functioning. Specifically, we examined antagonism as a predictor of prosocial behavior in a dictator game, and suspiciousness as a predictor of trust in the faith game.

MATERIALS AND METHODS

The study was preregistered and conducted online. The preregistration protocol is available at https://osf.io/er43j . Data and code are available at https://osf.io/2rvbg/ . Participants (N = 445) completed the German version of the Personality Inventory for DSM-5 to measure antagonism and suspiciousness. Additionally, they played the dictator game (more money taken away from another person indicates less prosocial behavior) and the faith game (choosing the sure choice instead of the faith choice indicates less trust). We conducted a linear regression model to test whether antagonism is associated with prosocial behavior in the dictator game and a logistic regression model to test whether suspiciousness predicts selection of the sure choice in the faith game.

RESULTS

As hypothesized, higher levels of antagonism were associated with less prosocial behavior in the dictator game. The remaining hypotheses were not supported, as suspiciousness was not significantly associated with the likelihood of choosing the sure choice in the faith game. Exploratory analyses on participants' estimates of the sure choice amount suggest successful experimental manipulation in the faith game.

CONCLUSIONS

The results on antagonism and prosocial behavior are consistent with those of previous studies that used categorial classification systems of personality disorders or examined non-pathological personality traits. Potential explanations for the non-significant effects of suspiciousness are discussed, including the small size and range of the sure choice payoff and that the anonymity of the game may have precluded suspicious traits from expressing. Future research with higher stakes and known interaction partners is needed to further probe the effects of suspiciousness.

The effect of delay and social distance in the dictator and ultimatum games

The previous research shows that delaying a reward in the dictator game contributes to less generous offers. If the reason for such results is temporal discounting, it can be expected that the effect of delay would be stronger for persons with a higher discounting rate, as well as the analogous pattern should occur in the ultimatum game. The participants of our study took decisions in the dictator and ultimatum game as proposers and responders. We manipulated delay of a reward (from immediate to in 5 years) and social distance (from the closest person to known only by sight). We observed the expected but weak interaction effect between delay and temporal discounting. However, the correlational analyses did not confirm the significant relationship between temporal discounting and decisions taken in dictator and ultimatum games. Moreover, the offers decline with the social distance, both in the dictator and ultimatum game. However, the social distance does not affect the value of the accepted offer in the ultimatum game. Such a discrepancy between donors' behaviour and beneficiaries' expectations may form a subtle but significant failure of the real-world donation markets.

Autism does not Dictate Children's Lack of Sharing in a Prosocial Choice Test

Studies have examined the association between theory of mind (ToM) and prosocial behavior in children with mixed results. A handful of studies have examined prosocial sharing behavior in children with autism, who typically exhibit ToM deficits. Studies using resource allocation tasks have generally failed to find significant differences between the sharing behavior of children with autism and neurotypical children. We presented 18 neurotypical children and 33 children with autism with the Dictator Game. Children had the opportunity to allocate toys in recipient present and absent conditions. Both groups donated more items in the recipient present versus absent condition and chose the prosocial option at above chance levels. Children with autism behave as prosocially as neurotypical children do in this paradigm.

The development of social comparisons and sharing behavior across 12 countries

Humans are social beings, and acts of prosocial behavior may be influenced by social comparisons. To study the development of prosociality and the impact of social comparisons on sharing, we conducted experiments with nearly 2500 children aged 3-12 years across 12 countries across five continents. Children participated in a dictator game where they had the opportunity to share up to 10 of their stickers with another anonymous child. Then, children were randomized to one of two treatments. In the "shared a little" treatment children were told that another child from their school had shared 1 sticker, whereas in the "shared a lot" treatment children were told that another child from their school had shared 6 stickers in the same game. There was a strong increase in baseline sharing with age in all countries and in both treatments. The "shared a lot" treatment had a positive treatment effect in increasing sharing overall, which varied across countries. However, cross-cultural comparisons did not yield expected significant differences between collectivist and individualist countries. Our results provide interesting evidence for the development of sharing behavior by age across the world and show that social information about the sharing of peers is important for children's decision making.

Automatic imitation does not predict levels of prosocial behaviour in a modified dictator game

Automatic imitation refers to the automatic tendency to imitate observed actions. Previous research on automatic imitation has linked it to a wide variety of social cognitive processes and functions, although the evidence is mixed and suggestive. However, no study to date has looked at the downstream behavioural effects of automatic imitation. The current research addresses this gap in the literature by exploring the possible relationship between trait-levels of automatic imitation, as measured by the automatic imitation task (AIT), and explicit prosocial behaviours, as measured by a modified dictator game (DG). Contrary to our expectations, AIT effects did not correlate with DG scores. This conclusion is supported by both equivalence tests and Bayesian analysis. However, we discuss a number of alternative explanations for our results, and caution against strong interpretations from a single study. We further discuss the implications of this finding in relation to the widespread notion that automatic imitation, and self-other control more generally, underlie social cognitive functions.

Oxytocin amplifies the influence of good intentions on social judgments

Studies have shown that the evolutionarily conserved neuropeptide oxytocin (OT) promotes various prosocial behaviors, yet there are few studies of the effect of OT on social judgments, especially on judgments when the actor's intention and the final outcome are incongruent. In a double-blind, placebo-controlled experiment, participants were asked to play the role of the recipient in a dictator game and to make social judgments about the dictator after intranasal OT administration. To isolate the outcome and the intention of the dictator's allocation, we developed a novel social judgment task in which recipients were told that 50% of the dictators' proposals would be reversed. The results showed that the effect of OT on social judgment was modulated by intention: OT increased goodness ratings only towards dictators with hyperfair intention. Our findings support the affiliative-motivation theory which states that OT enhances the affiliative motivation and recognition of positive-valence social stimuli.

Behavioral and electrophysiological responses to fairness norm violations in antisocial offenders

Antisocial personality disorder is characterized by a stable, lifelong pattern of disregard for and violation of others' rights. Disruptions in the representation of fairness norms may represent a key mechanism in the development and maintenance of this disorder. Here, we investigated fairness norm considerations and reactions to their violations. To examine electrophysiological correlates, we assessed the medial frontal negativity (MFN), an event-related potential previously linked to violations of social expectancy and norms. Incarcerated antisocial violent offenders (AVOs, n = 25) and healthy controls (CTLs, n = 24) acted as proposers in the dictator game (DG) and ultimatum game (UG) and received fair vs. unfair UG offers from either another human (social context) or a computer (non-social context). Results showed that AVOs made lower offers in the DG but not the UG, indicating more rational and strategic behavior. Most importantly, when acting as recipients in the UG, acceptance rates were modulated by social context in CTLs, while AVOs generally accepted more offers. Correspondingly, ERP data indicated pronounced MFN amplitudes following human offers in CTLs, whereas MFN amplitudes in AVOs were generally reduced. The current data suggest intact fairness norm representations but altered reactions to their violation in antisocial personality disorder.

Basal testosterone's relationship with dictator game decision-making depends on cortisol reactivity to acute stress: A dual-hormone perspective on dominant behavior during resource allocation

The dual-hormone hypothesis proposes that testosterone's relationship with status-seeking behavior is moderated by cortisol. However, research testing this hypothesis has focused on basal cortisol; the potential moderating effect of the acute cortisol response to stress has been largely overlooked. The present research investigated the moderating role of cortisol responses to an acute stressor on basal testosterone's link with dominant, status-relevant decision-making. Also, given the multifaceted nature of the response to acute stress, cardiovascular and affective responses to the stressor were examined as alternative moderators of the testosterone-behavior relationship. Participants (N = 112; 56% female) were exposed to a social-evaluative stressor, and their stress responses were measured. Participants subsequently engaged in a one-shot dictator game, wherein they were asked to split money ($10) with a confederate counterpart. The amount of money participants decided to keep for themselves was treated as a metric of dominant status-seeking behavior. For individuals who demonstrated lower cortisol responses to the stressor, basal testosterone was positively associated with more dominant behavior (i.e., keeping more money for oneself), but for those who showed higher cortisol responses, the testosterone-behavior relationship was suppressed. Moreover, other aspects of the stress response (i.e., cardiovascular and affective responses) did not moderate the relationship between basal testosterone and dictator game behavior. These results provide unique support for the dual-hormone hypothesis using markers of stress-induced cortisol change. The findings also suggest that the antagonistic effects of stress on testosterone's role in motivating status-relevant behavior may be specific to cortisol's role in the acute stress response.

Altruistic Behavior Depending on Opponents' Body Weight: An Experimental Approach

BACKGROUND

Obesity is a worldwide public health issue, not only because it is associated with numerous comorbid diseases but also because of its impact on the social level. This study aims to investigate (a) whether altruistic behavior differs between people with obesity and people who are not obese, (b) altruistic behavior toward people who are obese, in particular, women who are obese, and (c) implicit and explicit attitudes toward people with obesity as predictors for divergent altruistic behavior.

METHODS

An experimental approach called the dictator game was applied. In total, 168 participants of normal weight were asked to divide a monetary reward between themselves and two opponents, one person who was obese and one with normal weight. In addition, participants' implicit and explicit attitudes toward people with obesity as well as other sociodemographic data were assessed.

RESULTS

We found that altruistic behavior did not differ between obese and nonobese opponents (t(166) = -0.57, p = 0.71), nor did we find less altruistic attitudes toward women with obesity (t(85) = -0.03, p = 0.39). Linear regression models show less altruistic behavior among people with stronger explicit antifat attitudes (p = 0.015). However, although we found that participants held implicit attitudes toward people with obesity, these attitudes did not predict altruistic behavior toward people with obesity.

CONCLUSION

Although numerous studies reported discrimination toward people with obesity in several areas of life, we did not find discrimination in form of less altruistic behavior toward people with obesity. Moreover, although we found implicit antifat attitudes among the participants, these attitudes did not predict altruistic behavior toward people of divergent weight groups. Therefore, future research should investigate more intensively the diverse facets of discrimination toward people with obesity, if and to what extent implicit antifat attitudes have a quantifiable impact on the stigmatization and or discrimination process, and the hypotheses in a more hidden way, since manipulation check revealed that the majority of participants anticipated the underlying idea of the dictator game.

Empathy and altruistic behavior in antisocial violent offenders with psychopathic traits

Deficiencies in empathic functioning are considered a core characteristic of violent behavior. Enhancing empathy in aggressive populations may thus represent a promising intervention target. Hence, the aims of the present work were two-fold: First, we wanted to thoroughly assess empathic competencies and second, we aimed to investigate effects of an empathy induction on experienced empathy levels and prosocial behavior in a sample of violent offenders relative to matched controls. Empathy was assessed using both self-report as well as objective measures. For the empathy induction, participants were presented with empathy inducing and control videos. To assess the effects of the empathy induction on behavior, participants played a dictator game indicative of prosocial behavior after every video. Violent offenders showed no systematic impairment in empathy measures. Despite lower shares in the dictator game across conditions, the empathy induction led to a substantial increase in prosocial behavior in both groups. Importantly, high psychopathy scores were distinctively associated with lower self-reported empathy levels, an attenuated affective responsiveness to the empathy induction, and less altruistic behavior. Treatment programs aiming to improve empathy should take individual characteristics into account and may be applied to distinctive subgroups rather than to violent offenders per se.

Feel good, do good? Subjective well-being and sharing behavior among children

The current study examined the association between children's subjective well-being (SWB) and their sharing behavior. School children (second and fifth graders) were interviewed in private and had an opportunity to share candy with a recipient under one of two between-participants conditions: Perceived-High Obligation (a recipient in poverty) and Perceived-Low Obligation (a temporarily needy recipient). Results provide initial evidence of an increased association between SWB and sharing decisions with age; whereas SWB was not significantly correlated with the incidence of sharing by younger children (second graders), it was a positive predictor of sharing behavior among fifth graders. Manipulating the perceived obligation to share (by emphasizing the causes beyond the recipient's need), we found that higher levels of SWB were linked to sharing only in the Perceived-Low Obligation condition. Children with lower SWB behaved as expected by the norm and shared to a similar degree as children with higher SWB when sharing felt obligatory. However, when sharing was less obligatory, higher levels of SWB were linked to higher levels of sharing.

Dissociable roles of glucocorticoid and noradrenergic activation on social discounting

People often exhibit prosocial tendencies towards close kin and friends, but generosity decreases as a function of increasing social distance between donor and recipient, a phenomenon called social discounting. Evidence suggests that acute stress affects prosocial behaviour in general and social discounting in particular. We tested the causal role of the important stress neuromodulators cortisol (CORT) and noradrenaline (NA) in this effect by considering two competing hypotheses. On the one hand, it is possible that CORT and NA act in concert to increase generosity towards socially close others by reducing the aversiveness of the cost component in costly altruism and enhancing the emotional salience of vicarious reward. Alternatively, it is equally plausible that CORT and NA exert dissociable, opposing effects on prosocial behaviour based on prior findings implicating CORT in social affiliation, and NA in aggressive and antagonistic tendencies. We pharmacologically manipulated CORT and NA levels in a sample of men (N = 150) and found that isolated hydrocortisone administration promoted prosocial tendencies towards close others, reflected in an altered social discount function, but this effect was offset by concurrent noradrenergic activation brought about by simultaneous yohimbine administration. These results provide inceptive evidence for causal, opposing roles of these two important stress neuromodulators on prosocial behaviour, and give rise to the possibility that, depending on the neuroendocrine response profile, stress neuromodulator action can foster both tend-and-befriend and fight-or-flight tendencies at the same time.

Differential Fairness Decisions and Brain Responses After Expressed Emotions of Others in Boys with Autism Spectrum Disorders

Little is known about how emotions expressed by others influence social decisions and associated brain responses in autism spectrum disorders (ASD). We investigated the neural mechanisms underlying fairness decisions in response to explicitly expressed emotions of others in boys with ASD and typically developing (TD) boys. Participants with ASD adjusted their allocation behavior in response to the emotions but reacted less unfair than TD controls in response to happiness. We also found reduced brain responses in the precental gyrus in the ASD versus TD group when receiving happy versus angry reactions and autistic traits were positively associated with activity in the postcentral gyrus. These results provide indications for a role of precentral and postcentral gyrus in social-affective difficulties in ASD.

Friend versus foe: Neural correlates of prosocial decisions for liked and disliked peers

Although the majority of our social interactions are with people we know, few studies have investigated the neural correlates of sharing valuable resources with familiar others. Using an ecologically valid research paradigm, this functional magnetic resonance imaging study examined the neural correlates of prosocial and selfish behavior in interactions with real-life friends and disliked peers in young adults. Participants (N = 27) distributed coins between themselves and another person, where they could make selfish choices that maximized their own gains or prosocial choices that maximized outcomes of the other. Participants were more prosocial toward friends and more selfish toward disliked peers. Individual prosociality levels toward friends were associated negatively with supplementary motor area and anterior insula activity. Further preliminary analyses showed that prosocial decisions involving friends were associated with heightened activity in the bilateral posterior temporoparietal junction, and selfish decisions involving disliked peers were associated with heightened superior temporal sulcus activity, which are brain regions consistently shown to be involved in mentalizing and perspective taking in prior studies. Further, activation of the putamen was observed during prosocial choices involving friends and selfish choices involving disliked peers. These findings provide insights into the modulation of neural processes that underlie prosocial behavior as a function of a positive or negative relationship with the interaction partner.

From good institutions to generous citizens: Top-down incentives to cooperate promote subsequent prosociality but not norm enforcement

What makes people willing to pay costs to help others, and to punish others' selfishness? Why does the extent of such behaviors vary markedly across cultures? To shed light on these questions, we explore the role of formal institutions in shaping individuals' prosociality and punishment. In Study 1 (N=707), American participants who reported living under higher quality cooperation-enforcing institutions (police and courts) gave significantly more in a Dictator Game (DG), but did not punish significantly more in a Third-Party Punishment Game (TPPG). In Study 1R (N=1705), we replicated the positive relationship between reported institutional quality and DG giving observed in Study 1. In Study 2 (N=516), we experimentally manipulated institutional quality in a repeated Public Goods Game with a centralized punishment institution. Consistent with the correlational results of Study 1 and 1R, we found that centralized punishment led to significantly more prosociality in a subsequent DG compared to a no-punishment control, but had no significant direct effect on subsequent TPPG punishment (only an indirect effect via increased DG giving). Thus we present convergent evidence that the quality of institutions one is exposed to "spills over" to subsequent prosociality but not punishment. These findings support a theory of social heuristics, suggest boundary conditions on spillover effects of cooperation, and demonstrate the power of effective institutions for instilling habits of virtue and creating cultures of cooperation.

Human Cooperation and Its Underlying Mechanisms

Cooperation is a uniquely human behavior and can be observed across cultures. In order to maintain cooperative behavior in society, people are willing to punish deviant behavior on their own expenses and even without any personal benefits. Cooperation has been object of research in several disciplines. Psychologists, economists, sociologists, biologists, and anthropologists have suggested several motives possibly underlying cooperative behavior. In recent years, there has been substantial progress in understanding neural mechanisms enforcing cooperation. Psychological as well as economic theories were tested for their plausibility using neuroscientific methods. For example, paradigms from behavioral economics were adapted to be tested in the magnetic resonance imaging (MRI) scanner. Also, related brain functions were modulated by using transmagnetic brain stimulation (TMS). While cooperative behavior has often been associated with positive emotions, noncooperative behavior was found to be linked to negative emotions. On a neural level, the temporoparietal junction (TPJ), the striatum, and other reward-related brain areas have been shown to be activated by cooperation, whereas noncooperation has mainly been associated with activity in the insula.

Altruistic sharing behavior in children: Role of theory of mind and inhibitory control

This study aimed to assess altruistic sharing behavior in children aged 3 to 5, 6 to 8, and 9 to 11 years and to explore the involvement of potential cognitive mechanisms, namely theory of mind (ToM) and inhibitory control. A total of 158 children completed a dictator game with stickers as incentives. ToM was evaluated using a false belief task in preschoolers and the Strange Story Test in school-age children. Inhibitory control was assessed in preschoolers with the Day-Night task and in older children with the Stroop Color-Word Test. The result was that 48.10% of children aged 3 to 5 years decided to share, and the percentage rose significantly with increasing age. The difference in altruism level in children who decided to share among the three age groups was nonsignificant. These results suggest that mechanisms underlying the decision to share or not and altruistic behavior may be different. No significant linear relations were found between cognitive processes (i.e., ToM and inhibitory control) and sharing behavior. Surprisingly, 9- to 11-year-olds who shared 3 of 10 stickers performed worse in inhibitory control than did those who shared any other number of stickers. In conclusion, the proportion of children who decided to share, but not the level of altruism, increased with age. ToM was not involved in altruistic sharing, whereas inhibitory control may play a role when deciding how much to share.

What do we expect from a beauty? Facial attractiveness of the opposite sex gives rise to discrepancies in males' anticipation and demand

Facial attractiveness plays a significant role in social interactions and the effect of beauty premium is frequently observed. Previous studies showed that observing attractive counterparts would alleviate one's sense of unfairness. However, the mechanism underlying this phenomenon remained to be clarified. In this study, male participants were engaged in a modified Dictator game as recipients and their electroencephalograms were recorded. They were convinced that anonymous females who vary in facial attractiveness played as dictators. An outcome anticipation stage was implemented before proposed offers were presented and we focused on the cognitive process of subjective anticipation. A less negative Stimulus-preceding negativity was observed in the attractive face condition, suggesting that subjects paid less anticipatory attention toward proposed offers, and subjective expectation toward fair ones was weakened when beauties played as dictators. Thus, this study provides additional neural evidences for the beauty premium effect and suggests a reasonable explanation for this commonly reported phenomenon.

Using crowdsourced online experiments to study context-dependency of behavior

We use Mechanical Turk's diverse participant pool to conduct online bargaining games in India and the US. First, we assess internal validity of crowdsourced experimentation through variation of stakes ($0, $1, $4, and $10) in the Ultimatum and Dictator Game. For cross-country equivalence we adjust the stakes following differences in purchasing power. Our marginal totals correspond closely to laboratory findings. Monetary incentives induce more selfish behavior but, in line with most laboratory findings, the particular size of a positive stake appears irrelevant. Second, by transporting a homogeneous decision situation into various living conditions crowdsourced experimentation permits identification of context effects on elicited behavior. We explore context-dependency using session-level variation in participants' geographical location, regional affluence, and local social capital. Across "virtual pools" behavior varies in the range of stake effects. We argue that quasi-experimental variation of the characteristics people bring to the experimental situation is the key potential of crowdsourced online designs.

A neural signature of fairness in altruism: a game of theta?

In the dictator game, a proposer can share a certain amount of money between himself or herself and a receiver, who has no opportunity of influencing the offer. Rational choice theory predicts that dictators keep all money for themselves. But people often are offering money to receivers, despite their opportunity to maximize their own profit and therefore showing altruistic behavior. In this study, we investigated the influence of the altruism of the dictator, the anonymity of the decision and the income of the receiver on the offer made by a dictator. Additionally, we were interested in the influence of midfrontal theta activity prior to the offer, indicating the upcoming decision. The height of the offer made by the dictator was dependent on all variables investigated: Altruism of the dictator led to higher offers and income of the receiver led to higher offer the poorer the receivers are. The anonymity of the decision had two effects, depending on the altruism of the dictator, with higher offers for highly altruistic dictators, when they were not observed, and lower offers for less altruistic dictators in this condition. Finally, midfrontal theta activity predicts upcoming fair offers, maybe indicating altruistic motivation or empathy on physiological basis.

Testosterone dynamics and psychopathic personality traits independently predict antagonistic behavior towards the perceived loser of a competitive interaction

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.