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. In this article, we explain when negative interdependence is likely to arise and, crucially, the role played by (mis)perception in shaping an individual's understanding of their interdependent relationships. We argue that, owing to the difficulty in accurately perceiving interdependence with others, individuals might often be mistaken about the stake they hold in each other's outcomes, which can spark needless, resolvable forms of conflict. We then discuss when and how reducing misperceptions can help to resolve such conflicts. We argue that a key mechanism for resolving interdependent conflict, along with better sources of exogenous information, is to reduce reliance on heuristics such as stereotypes when assessing the nature of our interdependent relationships.

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. Individuals invested more in third-party helping than third-party punishment and invested more in both signals when observed compared to when investments would be unseen. We found no clear effect of partner choice (over and above mere observation) on investments in either punishment or helping. Third-parties who invested more than a partner were preferentially chosen for a subsequent Trust Game although the preference to interact with the higher investor was more pronounced in the help than in the punishment condition. Third-parties who invested more were entrusted with more money and investments in third-party punishment or helping reliably signalled trustworthiness. Individuals who did not invest in third-party helping were more likely to be untrustworthy than those who did not invest in third-party punishment. This supports the conception of punishment as a more ambiguous signal of cooperative intent compared to help.

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. We contend that the answer to both of these questions is yes. Most importantly, social behaviour in humans and other species operates under the same evolutionary framework. Moreover, we highlight how an open dialogue between different fields can inspire studies on humans and non-human species, leading to novel approaches and insights. Biology journals should encourage these discussions rather than drawing artificial boundaries between disciplines. Shared current and future challenges are to study helping in ecologically relevant contexts in order to correctly interpret how payoff matrices translate into inclusive fitness, and to integrate mechanisms into the hitherto largely functional theory. We can and should study human cooperation within a comparative framework in order to gain a full understanding of the evolution of helping.

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.

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. However, an alternative possibility exists: individuals may be more likely to punish atypical behaviour, because the cost of punishment generally increases with the number of individuals that are punished. We used a public goods game with third-party punishment to test whether punishment of defectors was reduced when defecting was typical, as predicted if punishment is responsive to norm violation. The cost of punishment was fixed, regardless of the number of players punished, meaning that it was not more costly to punish typical, relative to atypical, behaviour. Under these conditions, atypical behaviour was not punished more often than typical behaviour. In fact, most punishment was targeted at defectors, irrespective of whether defecting was typical or atypical. We suggest that the reduced punishment of defectors when they are common might often be explained in terms of the costs to the punisher, rather than responses to norm violators.

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. Conversely, impact deliberation was expected to increase the perceived trustworthiness of punishers but not helpers. Replicating previous work, we found that refraining from checking the personal cost of helping signals trustworthiness (although evidence for observers trusting uncalculating over calculating helpers was mixed). This did not extend to punishment: only uncalculating non-punishers were more trustworthy than cost-checking non-punishers. Impact deliberation results were mixed: deliberation affected the trust and trustworthiness of non-helpers more than helpers and no conclusive results were found for punishment. These results show that deliberation differentially affects assessments of those who help or punish others.

A positive effect of flowers rather than eye images in a large-scale, cross-cultural dictator game.

People often consider how their behaviour will be viewed by others, and may cooperate to avoid gaining a bad reputation. Sensitivity to reputation may be elicited by subtle social cues of being watched: previous studies have shown that people behave more cooperatively when they see images of eyes rather than control images. Here, we tested whether eye images enhance cooperation in a dictator game, using the online labour market Amazon Mechanical Turk (AMT). In contrast to our predictions and the results of most previous studies, dictators gave away more money when they saw images of flowers rather than eye images. Donations in response to eye images were not significantly different to donations under control treatments. Dictator donations varied significantly across cultures but there was no systematic variation in responses to different image types across cultures. Unlike most previous studies, players interacting via AMT may feel truly anonymous when making decisions and, as such, may not respond to subtle social cues of being watched. Nevertheless, dictators gave away similar amounts as in previous studies, so anonymity did not erase helpfulness. We suggest that eye images might only promote cooperative behaviour in relatively public settings and that people may ignore these cues when they know their behaviour is truly anonymous.

Male cleaner wrasses adjust punishment of female partners according to the stakes.

Punishment is an important deterrent against cheating in cooperative interactions. In humans, the severity of cheating affects the strength of punishment which, in turn, affects the punished individual's future behaviour. Here, we show such flexible adjustments for the first time in a non-human species, the cleaner wrasse (Labroides dimidiatus), where males are known to punish female partners. We exposed pairs of cleaners to a model client offering two types of food, preferred 'prawn' items and less-preferred 'flake' items. Analogous to interactions with real clients, eating a preferred prawn item ('cheating') led to model client removal. We varied the extent to which female cheating caused pay-off reduction to the male and measured the corresponding severity of male punishment. Males punished females more severely when females cheated during interactions with high value, rather than low value, model clients; and when females were similar in size to the male. This pattern may arise because, in this protogynous hermaphrodite, cheating by similar-sized females may reduce size differences to the extent that females change sex and become reproductive competitors. In response to more severe punishment from males, females behaved more cooperatively. Our results show that punishment can be adjusted to circumstances and that such subtleties can have an important bearing on the outcome of cooperative interactions.

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. Specifically, paranoid thoughts tend to be held in isolation and involve perceptions of harm to the self. Conspiracy beliefs, on the other hand, are shared by others and involve the perception of collective rather than personal harm. We discuss the similarities and differences between paranoia and conspiracy thinking and outline fruitful avenues for future research.

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. As a consequence, people frequently try to downplay their prosocial actions or hide them from others. In this review, we explore when and why investments in prosocial behaviour are likely to yield social costs. We propose two key features of interactions that make it more likely that generous individuals will incur social costs when: (a) observers infer that helpful behaviour is motivated by strategic or selfish motives; and (b) observers infer that helpful behaviour is detrimental to them. We describe how the cognition required to consider ulterior motives emerges over development and how these tendencies vary across cultures - and discuss how the potential for helpful actions to result in social costs might place boundaries on prosocial behaviour as well as limiting the contexts in which it might occur. We end by outlining the key avenues and priorities for future research.

Synchronous provisioning increases brood survival in cooperatively breeding pied babblers.

1. Behavioural synchrony typically involves trade-offs. In the context of foraging, for example, synchrony may be suboptimal when individuals have different energy requirements but yield net benefits in terms of increased foraging success or decreased predation risk. 2. Behavioural synchrony may also be advantageous when individuals collaborate to achieve a common goal, such as raising young. For example, in several bird species, provisioners synchronize nest-feeding visits. However, despite the apparent prevalence of provisioning synchrony, it is not known whether it is adaptive or what its function might be. 3. Here, we propose a novel explanation for provisioning synchrony: it increases brood survival by decreasing the number of temporally separate nest visits and accordingly the chance that the nest will be detected by predators. Using cooperatively breeding pied babblers, we showed experimentally that provisioners synchronized nest visits by waiting for another provisioner before returning to the nest. Brood survival increased with provisioning synchrony. Provisioners were more likely to synchronize feeding visits for older nestlings as they were louder and possibly more conspicuous to predators. Finally, provisioners in large groups were more likely to wait for other provisioners and synchronized a higher proportion of all visits than those in smaller groups. Thus, provisioning synchrony may be one mechanism by which large groups increase brood survival in this species. 4. This study highlights a novel strategy that birds use to increase the survival of young and demonstrates the advantages of coordinated behaviour in social species.

Higher reproductive skew among birds than mammals in cooperatively breeding species.

While competition for limited breeding positions is a common feature of group life, species vary widely in the extent to which reproduction is shared among females ('reproductive skew'). In recent years, there has been considerable debate over the mechanisms that generate variation in reproductive skew, with most evidence suggesting that subordinates breed when dominants are unable to prevent them from doing so. Here, we suggest that viviparity reduces the ability of dominant females to control subordinate reproduction and that, as a result, dominant female birds are more able than their mammal counterparts to prevent subordinates from breeding. Empirical data support this assertion. This perspective may increase our understanding of how cooperative groups form and are stabilized in nature.

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. Instead, punishment often prompts retaliation and punishment decisions frequently stem from competitive, rather than deterrent motives. Punishment decisions often reflect the desire to equalise or elevate payoffs relative to targets, rather than the desire to enact revenge for harm received or to deter cheats from reoffending in future. We therefore suggest that punishment also serves a competitive function, where what looks like spiteful behaviour actually allows punishers to equalise or elevate their own payoffs and/or status relative to targets independently of any change in the target's behaviour. Institutions that reduce or remove the possibility that punishers are motivated by relative payoff or status concerns might offer a way to harness these competitive motives and render punishment more effective at restoring cooperation.

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. Our hypothesis makes testable predictions about the environments in which paranoia should be most common as well as the developmental trajectory of paranoia across the lifespan. We suggest that paranoia should not solely be viewed as a pathological symptom of a mental disorder but also as a part of a normally-functioning human psychology.

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. We examined whether relative social status and perceived group affiliation, respectively, affect live paranoid thinking using two large-N (N = 2030), pre-registered experiments. Interacting with someone from a higher social rank or a political out-group led to an increase in paranoid attributions of harmful intent for ambiguous actions. Pre-existing paranoia predicted a general increase in harmful intent attribution, but there was no interaction with either type of social threat: highly paranoid people showed the same magnitude of increase as non-paranoid people, although from a higher baseline. We conclude social threat in the form of low social status and out-group status affects paranoid attributions, but ongoing paranoia represents a lowered threshold for detecting social threat rather than an impaired reactivity to it.

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'). Participants were allocated to the role of receiver or of an uninvolved observer; and evaluated to what extent they believed dictator decisions were motivated by (i) self-interest or (ii) harmful intent. All participants attributed more harmful intent to unfair as opposed to fair dictators. Paranoia had a positive effect on harmful intent attribution, for both fair and unfair dictators. Paranoia did not interact with attributions of self-interest. Importantly, highly paranoid participants attributed equally strong harmful intent to the dictator in the observer role as in the receiver role. This challenges the assumption that paranoia is mainly due to an exaggerated sense of personalised threat and suggests instead that paranoia involves a negative social representations of others.

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. Additionally, we varied whether children were told how much other children give (descriptive norm) or what they should give according to an adult (injunctive norm). Results showed that children generally gave more when they were exposed to a generous norm. However, patterns of compliance varied with age. Younger children were more likely to comply with the selfish norm, suggesting a licensing effect. By contrast, older children were more influenced by the generous norm, yet capped their donations at 50%, perhaps adhering to a pre-existing norm of equality. Children were not differentially influenced by descriptive or injunctive norms, suggesting a primacy of norm content over norm format. Together, our findings indicate that while generosity is malleable in children, normative information does not completely override pre-existing biases.

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. Choosers evaluated partners varying in quality (proxied by wealth) and fairness, in conditions when wealth was relatively stable or liable to change. When both partners were equally fair (or unfair), choosers typically preferred the richer partner. Nevertheless, when asked to choose between a rich-stingy and a poor-fair partner, choosers prioritized fairness over wealth-with this preference being particularly pronounced when wealth was unstable. The implications of these findings for real-world partner choice are discussed.

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. Nevertheless, these findings have not consistently replicated across different studies. Here, we suggest that considering country of origin-previously overlooked as a possible source of variation in responses-is important for understanding when and why individuals punish one another. We conducted a two-player stealing game with punishment, using data from 2,400 subjects recruited from the USA and India. US-based subjects punished in response to losses and disadvantageous inequality, but seldom invested in antisocial punishment (defined here as punishment of non-stealing partners). India-based subjects, on the other hand, punished at higher levels than US-based subjects and, so long as they did not experience disadvantageous inequality, punished stealing and non-stealing partners indiscriminately. Nevertheless, as in the USA, when stealing resulted in disadvantageous inequality, India-based subjects punished stealing partners more than non-stealing partners. These results are consistent with the hypothesis that variation in punitive behavior varies across societies, and support the idea that punishment might sometimes function to improve relative status, rather than to enforce cooperation.