Cooperation in humans: competition between groups and proximate emotions

Understanding the ultimate and proximate mechanisms that favour cooperation remains one of the greatest challenges in the biological and social sciences. A number of theoretical studies have suggested that competition between groups may have played a key role in the evolution of cooperation within human societies, and similar ideas have been discussed for other organisms, especially cooperative breeding vertebrates. However, there is a relative lack of empirical work testing these ideas. Our experiment found, in public goods games with humans, that when groups competed with other groups for financial rewards, individuals made larger contributions within their own groups. In such situations, participants were more likely to regard their group mates as collaborators rather than competitors. Variation in contribution among individuals, either with or without intergroup competition, was positively correlated with individuals' propensity to regard group mates as collaborators. We found that the levels of both guilt and anger individuals experienced were a function of their own contributions and those of their group mates. Overall, our results are consistent with the idea that the level of cooperation can be influenced by proximate emotions, which vary with the degree of intergroup competition.     

Public information for the assessment of quality: a widespread social phenomenon

We propose that the use of public information about the quality of environmental resources, obtained by monitoring the sampling behaviour of others, may be a widespread social phenomenon allowing individuals to make faster, more accurate assessments of their environment. To demonstrate this (i) we define public information and distinguish it from other kinds of social information; (ii) we review empirical work demonstrating the benefits and costs of using public information to estimate food patch quality; (iii) we examine recent work showing that individuals may also be using public information to improve their estimates of the quality of such disparate environmental parameters as breeding patches, opponents and mates; and finally (iv) we suggest avenues of future work to better understand the nature of public information use and when it might be used or ignored. Such work should lead to a more complete understanding of the behaviour of individuals in social aggregations.     

Coevolution of honest signaling and cooperative norms by cultural group selection

Evolution of cooperative norms is studied in a population where individual and group level selection are both in operation. Individuals play indirect reciprocity game within their group and follow second order norms. Individuals are norm-followers, and imitate their successful group mates. Aside from direct observation individuals can be informed about the previous actions and reputations by information transferred by others. A potential donor estimates the reputation of a potential receiver either by her own observation or by the opinion of the majority of others (indirect observation). Following a previous study (Scheuring, 2009) we assume that norms determine only the probabilities of actions, and mutants can differ in these probabilities. Similarly, we assume that individuals follow a stochastic information transfer strategy. The central question is whether cooperative norm and honest social information transfer can emerge in a population where initially only non-cooperative norms were present, and the transferred information was not sufficiently honest.It is shown that evolution can lead to a cooperative state where information transferred in a reliable manner, where generous cooperative strategies are dominant. This cooperative state emerges along a sharp transition of norms. We studied the characteristics of actions and strategies in this transition by classifying the stochastic norms, and found that a series of more and more judging strategies invade each other before the stabilization of the so-called generous judging strategy. Numerical experiments on the coevolution of social parameters (e.g. probability of direct observation and the number of indirect observers) reveal that it is advantageous to lean on indirect observation even if information transfer is much noisier than for direct observation, which is because to follow the majorities’ opinion suppresses information noise meaningfully.     

Calling by Concluding Sentinels: Coordinating Cooperation or Revealing Risk?

Efficient cooperation requires effective coordination of individual contributions to the cooperative behaviour. Most social birds and mammals involved in cooperation produce a range of vocalisations, which may be important in regulating both individual contributions and the combined group effort. Here we investigate the role of a specific call in regulating cooperative sentinel behaviour in pied babblers (Turdoides bicolor). 'Fast-rate chuck' calls are often given by sentinels as they finish guard bouts and may potentially coordinate the rotation of individuals as sentinels, minimising time without a sentinel, or may signal the presence or absence of predators, regulating the onset of the subsequent sentinel bout. We ask (i) when fast-rate chuck calls are given and (ii) what effect they have on the interval between sentinel bouts. Contrary to expectation, we find little evidence that these calls are involved in regulating the pied babbler sentinel system: observations revealed that their utterance is influenced only marginally by wind conditions and not at all by habitat, while observations and experimental playback showed that the giving of these calls has no effect on inter-bout interval. We conclude that pied babblers do not seem to call at the end of a sentinel bout to maximise the efficiency of this cooperative act, but may use vocalisations at this stage to influence more individually driven behaviours.     

The value of constant surveillance in a risky environment

In risky environments, where threats are unpredictable and the quality of information about threats is variable, all individuals face two fundamental challenges: balancing vigilance against other activities, and determining when to respond to warning signals. The solution to both is to obtain continuous estimates of background risk, enabling vigilance to be concentrated during the riskiest periods and informing about the likely cost of ignoring warnings. Human surveillance organizations routinely produce such estimates, frequently derived from indirect cues. Here we show that vigilant individuals in an animal society (the pied babbler, Turdoides bicolor) perform a similar role. We ask (i) whether, in the absence of direct predator threats, pied babbler sentinels react to indirect information associated with increased risk and whether they communicate this information to group mates; (ii) whether group mates use this information to adjust their own vigilance, and whether this influences foraging success; and (iii) whether information provided by sentinels reduces the likelihood of inappropriate responses to alarm calls. Using playback experiments, we show that: (i) sentinels reacted to indirect predator cues (in the form of heterospecific alarm calls) by giving graded surveillance calls; (ii) foragers adjusted their vigilance in reaction to changes in surveillance calls, with substantial effects on foraging success; and (iii) foragers reduced their probability of responding to alarm calls when surveillance calls indicated lowered risk. These results demonstrate that identifying attacks as they occur is only part of vigilance: equally important is continuous surveillance providing information necessary for individuals to make decisions about their own vigilance and evasive action. Moreover, they suggest that a major benefit of group living is not only the increased likelihood of detecting threats, but a marked improvement in the quality of information available to each individual.     

Florida Scrub-Jays Compensate for the Sentinel Behavior of Flockmates

Sentinel coordination requires that individuals react to the sentinel behavior of others. Previous work showed that Florida scrub‐jays are sentinels more often when given supplemental food. Here we measured how birds in pairs reacted when their mates were fed. Scrub‐jays were sentinels less when their mates were fed, demonstrating compensation. Indirect evidence suggests that this compensatory decrease in sentinel behavior was smaller than the increase in sentinel behavior by their mates. In addition, males in newly established groups were sentinels less often.     

Do great tits assess rivals by combining direct experience with information gathered by eavesdropping?

Animals frequently use signals that travel further than the spacing between individuals. For every intended recipient of a given signal there are likely to be many other individuals that receive information. Eavesdropping on signalling interactions between other individuals provides a relatively cost-free method of assessing future opponents or mates. Male great tits (Parus major) extract relative information from such interactions between individuals unknown to them. Here, we show that male great tits can take information gathering a stage further and obtain more information about a previously unencountered intruder, by the hitherto unknown capability of combining information gathered by eavesdropping with that derived from their own direct interaction with an individual. Prior experience with an intruder (A) was achieved by subjecting a focal male to different levels of intrusion simulated using interactive playback. This intruder (A) then took part in a simulated interaction with an unknown male (B) outside the territorial boundary of the focal males. In response to subsequent intrusion by the second male (B), focal males showed low song output in response to males that had lost to a male that the subject was able to beat. Males of known high quality, or those about which information was ambiguous, elicited a high level of song output by focal males. We discuss the implications of this finding for the evolution of communication and social behaviour.     

You're not my type: Do conservatives have a bias for seeing long-term mates?

When choosing a mate, humans favour genetic traits (attractiveness, high sex drive) for short-term relationships and parental traits (warmth, high status) for long-term relationships. These preferences serve to maximise fitness of future offspring. But this model neglects the role of social norms in shaping evolved mating strategies. For example, in conservative cultures, individuals are likely to face costs such as punishment for short-term mating. Here we show that conservatives over-perceive some mates' suitability as long-term partners. Study 1 found that conservatives were less likely to use a short-term strategy that was distinctive from their long-term strategy. Study 2 showed that conservatives over-perceived hypothetical mates as long-term investing partners, despite their lack of commitment-compatible traits. Conservatism was measured at the regional- (India, USA, UK) and individual-level. Our results demonstrate how social norms may bias behaviour. We anticipate our findings to be a starting point for more sophisticated models, drawing on developments from evolutionary and social psychology.     

Hidden altruism in a real-world setting

Concerns for reputation can promote cooperative behaviour. Individuals that behave cooperatively stand to benefit if they gain in influence, status or are more likely to be chosen as interaction partners by others. Most theoretical and empirical models of cooperation predict that image score will increase with cooperative contributions. Individuals are therefore expected to make higher contributions when observed by others and should opt to make contributions publicly rather than privately, particularly when contributions are higher than average. Here, however, I find the opposite effect. Using data from an online fundraising website, I show that donors are more likely to opt for anonymity when making extremely low and extremely high donations. Mid-range donations, on the other hand, are typically publicized. Recent work has shown that extremely generous individuals may be ostracized or punished by group members. The data presented here suggest that individuals may hide high donations to avoid these repercussions.     

Cooperating in the face of uncertainty: a consistent framework for understanding the evolution of cooperation

The evolution of cooperative behaviour, whereby individuals enhance the fitness of others at an apparent cost to themselves, represents one of the greatest paradoxes of evolution. Individuals that engage in such cooperative behaviour can, however, be favoured by natural selection if cooperative actions confer higher fitness than alternative actions. To understand the evolution of cooperative behaviour, the direct and indirect genetic benefits that individuals accrue in the present and future must be summed - this can be accomplished without any reference to the colorful vocabulary typically associated with studies of cooperation. When benefits are accrued indirectly through relatives or directly in the future individuals must be able to assess and enhance their probability of accruing those benefits and behave accordingly. We suggest that, in the same way that studies of kin recognition systems improved our understanding of how individuals assess and enhance their probability of accruing indirect benefits, studies of various forms of inheritance and reciprocation recognition systems will improve our understanding of how individuals assess and enhance their probability of accruing future benefits. Recognizing the parallel between studies of indirect fitness and future fitness, at multiple levels of analysis, will move us toward a simpler and more consistent framework for understanding the evolution of cooperative behaviour.     

When cooperation begets cooperation: the role of key individuals in galvanizing support

Life abounds with examples of conspecifics actively cooperating to a common end, despite conflicts of interest being expected concerning how much each individual should contribute. Mathematical models typically find that such conflict can be resolved by partial-response strategies, leading investors to contribute relatively equitably. Using a case study approach, we show that such model expectations can be contradicted in at least four disparate contexts: (i) bi-parental care; (ii) cooperative breeding; (iii) cooperative hunting; and (iv) human cooperation. We highlight that: (a) marked variation in contributions is commonplace; and (b) individuals can often respond positively rather than negatively to the contributions of others. Existing models have surprisingly limited power in explaining these phenomena. Here, we propose that, although among-individual variation in cooperative contributions will be influenced by differential costs and benefits, there is likely to be a strong genetic or epigenetic component. We then suggest that selection can maintain high investors (key individuals) when their contributions promote support by increasing the benefits and/or reducing the costs for others. Our intentions are to raise awareness in—and provide testable hypotheses of—two of the most poorly understood, yet integral, questions regarding cooperative ventures: why do individuals vary in their contributions and when does cooperation beget cooperation?     

Meerkat helpers do not specialize in particular activities

Differences in the relative contributions of individual helpers to cooperative activities in vertebrate societies are sometimes interpreted as evidence of functional specialization and have been compared with the incipient subcaste systems found in some social insects. However, it is not yet clear whether some helpers specialize in particular tasks throughout their life span or whether variation in cooperative behaviour represents a temporary, age-related polyethism. We describe the development of cooperative behaviour in female helpers in meerkats, Suricata suricatta, an obligately cooperative mammal where young produced by the dominant female are reared by up to 30 helpers. Using a combination of field experiments and long-term records of the development of individuals, we investigated whether particular helpers specialize in particular activities. In the first year of life, variation in body weight affected overall levels of involvement in cooperative behaviour as well as relative contributions to different activities, generating contrasting activity profiles between light and heavy helpers. However, the effects of body weight disappeared by the second year of life, and individual differences in foraging success became the principal factor affecting contributions to cooperative behaviour. Contributions to different cooperative activities were positively correlated across individuals, with some helpers consistently contributing more than others to all cooperative activities. Our study provides no evidence that meerkat helpers specialize in particular cooperative activities.     

Previous experiences shape adaptive mate preferences

Existing models of mate choice assume that individuals haveperfect knowledge of their own ability to attract a mate andcan adjust their preferences accordingly. However, real animalswill typically be uncertain of their own attractiveness. A potentiallyuseful source of information on this is the feedback from previousencounters with potential mates. Here, we develop a dynamicmodel of mutual mate choice in which both males and femalesare initially ignorant of their own attractiveness. Individualssequentially sample potential mates and retain some informationabout the outcome of these encounters (e.g., the number of timesthey are accepted or rejected). We use a simplified processof mutation and selection to evolve an adaptive strategy formate choice under these conditions. The stable strategy we findis the one in which individuals are sensitive to this previousexperience, adjusting their mate preferences according to theinterest received from members of the opposite sex. In general,experiences of rejection tend to reduce choosiness, whereasexperiences of acceptance tend to increase it. Sensitivity toprevious experiences allows individuals to exercise a prudentmate-choice strategy in which their preferences are graduallytuned to their prospects on the mating market. This flexibilityis based on simple rules and does not require sophisticatedcognitive abilities. Our basic predictions can be tested insystems where both males and females are choosy, and it is possibleto manipulate the level of interest shown by potential mates.     

The effect of energy reserves on social foraging: hungry sparrows scrounge more

Animals often use alternative strategies when they compete for resources, but it is unclear in most cases what factors determine the actual tactic followed by individuals. Although recent models suggest that the internal state of animals may be particularly important in tactic choice, the effects of state variables on the use of alternative behavioural forms have rarely been demonstrated. In this study, using experimental wind exposure to increase overnight energy expenditure, we show that flock-feeding house sparrows (Passer domesticus) with lowered energy reserves increase their use of scrounging (exploiting others' food findings) during their first feed of the day. This result is in accordance with the prediction of a state-dependent model of use of social foraging tactics. We also show that scrounging provides less variable feeding rates and patch finding times than the alternative tactic. These latter results support the theoretical assumption that scrounging is a risk-averse tactic, i.e. it reduces the risk of immediate starvation. As the level of energy reserves predicts the use of social foraging tactics, we propose that selection should favour individuals that monitor the internal state of flock mates and use this information to adjust their own tactic choice.     

Variation in contributions to teaching by meerkats

Recent evidence from cooperative insect, bird and mammal societies has challenged the assumption that teaching is restricted to humans. However, little is known about the factors affecting the degree to which individuals in such societies contribute to teaching. Here, I examine variation in contributions to teaching in meerkats, where older group members teach pups to handle difficult prey. I show that investment in teaching varies with characteristics of pups, helpers, groups and ecological conditions. Although prior experience in caring for pups did not significantly influence teaching behaviour, younger helpers, which were still investing in growth, contributed less to teaching than older individuals. This suggests that, in common with other cooperative activities, contributions to teaching vary with the costs experienced by individual group members. However, in contrast to other forms of helping in meerkats, I detected no effects of nutritional state on teaching, suggesting that it carries relatively low costs. In species where individuals can potentially gain direct or indirect fitness benefits from facilitating learning in others, low costs divided among multiple group members may help tip the balance towards selection for teaching.     

Males adjust their signalling behaviour according to experience of male signals and male–female signal duets

Sexual signals are conspicuous sources of information about neighbouring competitors, and species in which males and females signal during pair formation provide various sources of public information to which individuals can adjust their behaviour. We performed two experiments with a duetting vibrational insect, Enchenopa binotata treehoppers (Hemiptera: Membracidae), to ask whether males adjust their signalling behaviour according to (1a) their own experience of competitors' signals, (1b) how females adjust their mate preferences on the basis of their experience of male signals (described in prior work), and/or (2) their own experience of female response signals to competitors' signals. We presented males with synthetic male signals of different frequencies and combinations thereof for 2 weeks. We recorded males a day after their last signal exposure, finding that (1a) male signal rate increased in response to experience of attractive competitors, but that (1b) male signal frequency did not shift in a manner consistent with how females adjust their mate preferences in those experience treatments. Second, we presented males with different male–female duets for 2 weeks, finding that (2) male signal length increased from experience of female duets with attractive competitors. Males thus make two types of adjustment according to two sources of public information: one provided by experience of male signals and another by experience of female responses to male signals. Signalling plasticity can generate feedback loops between the adjustments that males and females make, and we discuss the potential consequences of such feedback loops for the evolution of communication systems.     

Consistent individual differences in cooperative behaviour in meerkats (Suricata suricatta)

Although recent models for the evolution of personality, using game theory and life‐history theory, predict that individuals should differ consistently in their cooperative behaviour, consistent individual differences in cooperative behaviour have rarely been documented. In this study, we used a long‐term data set on wild meerkats to quantify the repeatability of two types of cooperative care (babysitting and provisioning) within individuals and examined how repeatability varied across age, sex and status categories. Contributions to babysitting and provisioning were significantly repeatable and positively correlated within individuals, with provisioning more repeatable than babysitting. While repeatability of provisioning was relatively invariant across categories of individuals, repeatability of babysitting increased with age and was higher for subordinates than dominants. These results provide support for theoretical predictions that life‐history trade‐offs favour the evolution of consistent individual differences in cooperative behaviour and raise questions about why some individuals consistently help more than others across a suite of cooperative behaviours.     

Common knowledge promotes cooperation in the threshold public goods game by reducing uncertainty

Recent work suggests that an important cognitive mechanism promoting coordination is common knowledge—a heuristic for representing recursive mental states. Yet, we know little about how common knowledge promotes coordination. We propose that common knowledge increases coordination by reducing uncertainty about others' cooperative behavior. We examine how common knowledge increases cooperation in the context of a threshold public goods game, a public good game in which a minimum level of contribution—a threshold—is required. Across three preregistered studies (N = 5580), we explored how varying (1) the information participants had regarding what their group members knew about the threshold and (2) the threshold level affected contributions. We found that participants were more likely to contribute to the public good when there was common knowledge of the threshold than private knowledge. Participants' predictions about the number of group members contributing to the public good and their certainty ratings of those predictions mediated the effect of information condition on contributions. Our results suggest that common knowledge of the threshold increases public good contributions by reducing uncertainty around other people's cooperative behavior. These findings point to the influential role of common knowledge in helping to solve large-scale cooperation problems.     

Monitoring of group mates in relation to their behavior in mandrills

Primates are known to have considerable knowledge about the social relationships that link their group mates and are likely to derive this information from observing the social interactions that occur in their social group. They may, therefore, be hypothesized to pay particular attention to the social interactions involving group mates. In this study, we evaluated how the attention captive mandrills (Mandrillus sphinx) devote to their group mates was modulated by the behavior of the latter. Mandrills looked most frequently at foraging individuals and least frequently at sleeping individuals. Mandrills also looked at grooming individuals more than at individuals that were simply sitting in contact. Grooming dyads were looked at regardless of the social rank and kinship of the individuals involved. These results contribute to our understanding of how primates obtain their social knowledge.     

Cooperative sentinel calling? Foragers gain increased biomass intake

Many foraging animals face a fundamental tradeoff between predation and starvation. In a range of social species, this tradeoff has probably driven the evolution of sentinel behavior, where individuals adopt prominent positions to watch for predators while groupmates forage. Although there has been much debate about whether acting as a sentinel is a selfish or cooperative behavior, far less attention has focused on why sentinels often produce quiet vocalizations (hereafter known as "sentinel calls") to announce their presence. We use observational and experimental data to provide the first evidence that group members gain an increase in foraging success by responding to these vocal cues given by sentinels. Foraging pied babblers (Turdoides bicolor) spread out more, use more exposed patches, look up less often, and spend less time vigilant in response to sentinel calling. Crucially, we demonstrate that these behavioral alterations lead to an increase in biomass intake by foragers, which is likely to enhance survival. We argue that this benefit may be the reason for sentinel calling, making it a truly cooperative behavior.