No evidence for inequity aversion in non-human animals: a meta-analysis of accept/reject paradigms.

Disadvantageous inequity aversion (IA), a negative response to receiving less than others, is a key building block of the human sense of fairness. While some theorize that IA is shared by species across the animal kingdom, others argue that it is an exclusively human evolutionary adaptation to the selective pressures of cooperation among non-kin. Essential to this debate is the empirical question of whether non-human animals are averse towards unequal resource distributions.

Acting without considering personal costs signals trustworthiness in helpers but not punishers.

Third-party punishment and helping can signal trustworthiness, but the interpretation of deliberation may vary: uncalculated help signals trustworthiness, but this may not hold for punishment. Using online experiments, we measured how deliberation over personal costs and impacts to targets affected the trustworthiness of helpers and punishers. We expected that personal cost-checking punishers and helpers would be trusted less.

Resolving selfish and spiteful interdependent conflict.

Interdependence occurs when individuals have a stake in the success or failure of others, such that the outcomes experienced by one individual also generate costs or benefits for others. Discussion on this topic has typically focused on positive interdependence (where gains for one individual result in gains for another) and on the consequences for cooperation. However, interdependence can also be negative (where gains for one individual result in losses for another), which can spark conflict.

Paranoia and conspiracy thinking.

Paranoia and conspiracy thinking share many risk factors, such as victimization, poverty and social isolation. They also have many phenomenological features in common, including heightened tendency to attribute negative outcomes to malevolent agents and idiosyncratic pattern detection. Nevertheless, paranoia and conspiracy thinking also differ in key respects.

Third-party punishers do not compete to be chosen as partners in an experimental game.

Third-party punishment is thought to act as an honest signal of cooperative intent and such signals might escalate when competing to be chosen as a partner. Here, we investigate whether partner choice competition prompts escalating investment in third-party punishment. We also consider the case of signalling via helpful acts to provide a direct test of the relative strength of the two types of signals.

No good deed goes unpunished: the social costs of prosocial behaviour.

Performing costly helpful behaviours can allow individuals to improve their reputation. Those who gain a good reputation are often preferred as interaction partners and are consequently better able to access support through cooperative relationships with others. However, investing in prosocial displays can sometimes yield social costs: excessively generous individuals risk losing their good reputation, and even being vilified, ostracised or antisocially punished.

Punishment: one tool, many uses.

Humans are outstanding in their ability to cooperate with unrelated individuals, and punishment - paying a cost to harm others - is thought to be a key supporting mechanism. According to this view, cooperators punish defectors, who respond by behaving more cooperatively in future interactions. However, a synthesis of the evidence from laboratory and real-world settings casts serious doubts on the assumption that the sole function of punishment is to convert cheating individuals into cooperators.

An evolutionary perspective on paranoia.

Paranoia is the most common symptom of psychosis but paranoid concerns occur throughout the general population. Here, we argue for an evolutionary approach to paranoia across the spectrum of severity that accounts for its complex social phenomenology - including the perception of conspiracy and selective identification of perceived persecutors - and considers how it can be understood in light of our evolved social cognition. We argue that the presence of coalitions and coordination between groups in competitive situations could favour psychological mechanisms that detect, anticipate and avoid social threats.

Experimentally induced social threat increases paranoid thinking.

The ability to attribute intentions to others is a hallmark of human social cognition but is altered in paranoia. Paranoia is the most common positive symptom of psychosis but is also present to varying degrees in the general population. Epidemiological models suggest that psychosis risk is associated with low social rank and minority status, but the causal effects of status and group affiliation on paranoid thinking remain unclear.

Helping in humans and other animals: a fruitful interdisciplinary dialogue.

Humans are arguably unique in the extent and scale of cooperation with unrelated individuals. While pairwise interactions among non-relatives occur in some non-human species, there is scant evidence of the large-scale, often unconditional prosociality that characterizes human social behaviour. Consequently, one may ask whether research on cooperation in humans can offer general insights to researchers working on similar questions in non-human species, and whether research on humans should be published in biology journals.

Paranoia and the social representation of others: a large-scale game theory approach.

Current definitions of paranoia include two key components: unfounded ideas of harm and the idea that the harm is intended by others. However, attributions of harmful intent have been poorly studied and mainly using artificial scenarios rather than participation in genuine social interactions where genuine resources are at stake. Using a large non-clinical population (N = 3229) recruited online, we asked people to complete a measure of paranoid ideation before playing a modified Dictator Game, where the 'dictator' can allocate money to the partner (the 'receiver').

Children are sensitive to norms of giving.

People across societies engage in costly sharing, but the extent of such sharing shows striking cultural variation, highlighting the importance of local norms in shaping generosity. Despite this acknowledged role for norms, it is unclear when they begin to exert their influence in development. Here we use a Dictator Game to investigate the extent to which 4- to 9-year-old children are sensitive to selfish (give 20%) and generous (give 80%) norms.

Exploring the trade-off between quality and fairness in human partner choice.

Partner choice is an important force underpinning cooperation in humans and other animals. Nevertheless, the mechanisms individuals use to evaluate and discriminate among partners who vary across different dimensions are poorly understood. Generally, individuals are expected to prefer partners who are both able and willing to invest in cooperation but how do individuals prioritize the ability over willingness to invest when these characteristics are opposed to one another? We used a modified Dictator Game to tackle this question.

Exploring the Motivations for Punishment: Framing and Country-Level Effects.

Identifying the motives underpinning punishment is crucial for understanding its evolved function. In principle, punishment of distributional inequality could be motivated by the desire to reciprocate losses ('revenge') or by the desire to reduce payoff asymmetries between the punisher and the target ('inequality aversion'). By separating these two possible motivations, recent work suggests that punishment is more likely to be motivated by disadvantageous inequality aversion than by a desire for revenge.

Power Asymmetries and Punishment in a Prisoner's Dilemma with Variable Cooperative Investment.

In many two-player games, players that invest in punishment finish with lower payoffs than those who abstain from punishing. These results question the effectiveness of punishment at promoting cooperation, especially when retaliation is possible. It has been suggested that these findings may stem from the unrealistic assumption that all players are equal in terms of power.

The proximate-ultimate confusion in teaching and cooperation.

Kline does an admirable job of extending the functionalist framework developed by comparative researchers to help understand the function and form of human teaching. Functionalist approaches consider the adaptive value and underlying mechanisms of behaviour as separate but complementary questions, avoiding the conflation of ultimate and proximate explanations that has long hindered research on teaching and other forms of cooperation.

Competitive helping in online giving.

Unconditional generosity in humans is a puzzle. One possibility is that individuals benefit from being seen as generous if there is competition for access to partners and if generosity is a costly-and therefore reliable-signal of partner quality [1-3]. The "competitive helping" hypothesis predicts that people will compete to be the most generous, particularly in the presence of attractive potential partners [1].

Third-party punishers are rewarded, but third-party helpers even more so.

Punishers can benefit from a tough reputation, where future partners cooperate because they fear repercussions. Alternatively, punishers might receive help from bystanders if their act is perceived as just and other-regarding. Third-party punishment of selfish individuals arguably fits these conditions, but it is not known whether third-party punishers are rewarded for their investments.

Why humans might help strangers.

Humans regularly help strangers, even when interactions are apparently unobserved and unlikely to be repeated. Such situations have been simulated in the laboratory using anonymous one-shot games (e.g.

The effect of power asymmetries on cooperation and punishment in a prisoner's dilemma game.

Recent work has suggested that punishment is detrimental because punishment provokes retaliation, not cooperation, resulting in lower overall payoffs. These findings may stem from the unrealistic assumption that all players are equal: in reality individuals are expected to vary in the power with which they can punish defectors. Here, we allowed strong players to interact with weak players in an iterated prisoner's dilemma game with punishment.

The reputation of punishers.

Punishment is a potential mechanism to stabilise cooperation between self-regarding agents. Theoretical and empirical studies on the importance of a punitive reputation have yielded conflicting results. Here, we propose that a variety of factors interact to explain why a punitive reputation is sometimes beneficial and sometimes harmful.

Dictator Game Giving: The Importance of Descriptive versus Injunctive Norms.

Human behaviour is influenced by social norms but norms can entail two types of information. Descriptive norms refer to what others do in this context, while injunctive norms refer to what ought to be done to ensure social approval. In many real-world situations these norms are often presented concurrently meaning that their independent effects on behaviour are difficult to establish.

Defectors, not norm violators, are punished by third-parties.

Punishment of defectors and cooperators is prevalent when their behaviour deviates from the social norm. Why atypical behaviour is more likely to be punished than typical behaviour remains unclear. One possible proximate explanation is that individuals simply dislike norm violators.

Genetic monogamy despite variable ecological conditions and social environment in the cooperatively breeding apostlebird.

Mating strategies may be context-dependent and may vary across ecological and social contexts, demonstrating the role of these factors in driving the variation in genetic polyandry within and among species. Here, we took a longitudinal approach across 5 years (2006-2010), to study the apostlebird (Struthidea cinerea), an Australian cooperatively breeding bird, whose reproduction is affected by ecological "boom and bust" cycles. Climatic variation drives variation in the social (i.