What's in it for me? Self-regard precludes altruism and spite in chimpanzees

Sensitivity to fairness may influence whether individuals choose to engage in acts that are mutually beneficial, selfish, altruistic, or spiteful. In a series of three experiments, chimpanzees (Pan troglodytes) could pull a rope to access out-of-reach food while concomitantly pulling another piece of food further away. In the first study, they could make a choice that solely benefited themselves (selfishness), or both themselves and another chimpanzee (mutualism). In the next two experiments, they could choose between providing food solely for another chimpanzee (altruism), or for neither while preventing the other chimpanzee from receiving a benefit (spite). The main result across all studies was that chimpanzees made their choices based solely on personal gain, with no regard for the outcomes of a conspecific. These results raise questions about the origins of human cooperative behaviour.     

Sequential Tool Use in Great Apes

Sequential tool use is defined as using a tool to obtain another non-food object which subsequently itself will serve as a tool to act upon a further (sub)goal. Previous studies have shown that birds and great apes succeed in such tasks. However, the inclusion of a training phase for each of the sequential steps and the low cost associated with retrieving the longest tools limits the scope of the conclusions. The goal of the experiments presented here was, first to replicate a previous study on sequential tool use conducted on New Caledonian crows and, second, extend this work by increasing the cost of retrieving a tool in order to test tool selectivity of apes. In Experiment 1, we presented chimpanzees, orangutans and bonobos with an out-of-reach reward, two tools that were available but too short to reach the food and four out-of-reach tools differing in functionality. Similar to crows, apes spontaneously used up to 3 tools in sequence to get the reward and also showed a strong preference for the longest out-of reach tool independently of the distance of the food. In Experiment 2, we increased the cost of reaching for the longest out-of reach tool. Now apes used up to 5 tools in sequence to get the reward and became more selective in their choice of the longest tool as the costs of its retrieval increased. The findings of the studies presented here contribute to the growing body of comparative research on tool use.     

Chimpanzee social intelligence: selfishness,altruism, and the mother–infant bond

To better understand the human mind from an evolutionary perspective, a great deal of research has focused on the closest living relative of humans, the chimpanzee, using various approaches, including studies of social intelligence. Here, I review recent research related to several aspects of social intelligence, including deception, understanding of perception and intention, social learning, trading, cooperation, and regard for others. Many studies have demonstrated that chimpanzees are proficient in using their social intelligence for selfish motives to benefit from their interactions with others. In contrast, it is not yet clear whether chimpanzees engage in prosocial behaviors that benefit others; however, chimpanzee mother–infant interactions indicate the possibility of such behaviors. Therefore, I propose that chimpanzees possess rudimentary traits of human mental competence not only in terms of theory of mind in a broader sense but also in terms of prosociality involving regard for others. Mother–infant interactions appear to be particularly important to understanding the manifestation of social intelligence from an evolutionary perspective.     

Tactical use of unimodal and bimodal communication by chimpanzees, Pan troglodytes

Do chimpanzees tailor their communication in accordance with the attentional status of a human observer? We presented 57 chimpanzees with three experimental conditions in randomized order: an experimenter offered a banana to the focal subject (Focal), to a cagemate of the focal subject (In-Cage) and to a chimpanzee in an adjacent cage (Adjacent) while a second experimenter recorded the first and second responses of the focal subject in all three conditions. The chimpanzees' behaviour was mostly visual or bimodal in the Focal condition, changing to auditory behaviour or disengagement in the In-Cage and Adjacent conditions. Thus, with no explicit training and on their first trials in all instances, the chimpanzees tactically deployed their communicative behaviours in the visual and auditory domains in accordance with the manipulated attentional and intentional status of a human observer.     

An Evolutionary Model of Cooperation,Fairness and Altruistic Punishment in Public Good Games

We identify and explain the mechanisms that account for the emergence of fairness preferences and altruistic punishment in voluntary contribution mechanisms by combining an evolutionary perspective together with an expected utility model. We aim at filling a gap between the literature on the theory of evolution applied to cooperation and punishment, and the empirical findings from experimental economics. The approach is motivated by previous findings on other-regarding behavior, the co-evolution of culture, genes and social norms, as well as bounded rationality. Our first result reveals the emergence of two distinct evolutionary regimes that force agents to converge either to a defection state or to a state of coordination, depending on the predominant set of self- or other-regarding preferences. Our second result indicates that subjects in laboratory experiments of public goods games with punishment coordinate and punish defectors as a result of an aversion against disadvantageous inequitable outcomes. Our third finding identifies disadvantageous inequity aversion as evolutionary dominant and stable in a heterogeneous population of agents endowed initially only with purely self-regarding preferences. We validate our model using previously obtained results from three independently conducted experiments of public goods games with punishment.     

Fairness expectations and altruistic sharing in 15-month-old human infants

Human cooperation is a key driving force behind the evolutionary success of our hominin lineage. At the proximate level, biologists and social scientists have identified other-regarding preferences--such as fairness based on egalitarian motives, and altruism--as likely candidates for fostering large-scale cooperation. A critical question concerns the ontogenetic origins of these constituents of cooperative behavior, as well as whether they emerge independently or in an interrelated fashion. The answer to this question will shed light on the interdisciplinary debate regarding the significance of such preferences for explaining how humans become such cooperative beings. We investigated 15-month-old infants' sensitivity to fairness, and their altruistic behavior, assessed via infants' reactions to a third-party resource distribution task, and via a sharing task. Our results challenge current models of the development of fairness and altruism in two ways. First, in contrast to past work suggesting that fairness and altruism may not emerge until early to mid-childhood, 15-month-old infants are sensitive to fairness and can engage in altruistic sharing. Second, infants' degree of sensitivity to fairness as a third-party observer was related to whether they shared toys altruistically or selfishly, indicating that moral evaluations and prosocial behavior are heavily interconnected from early in development. Our results present the first evidence that the roots of a basic sense of fairness and altruism can be found in infancy, and that these other-regarding preferences develop in a parallel and interwoven fashion. These findings support arguments for an evolutionary basis--most likely in dialectical manner including both biological and cultural mechanisms--of human egalitarianism given the rapidly developing nature of other-regarding preferences and their role in the evolution of human-specific forms of cooperation. Future work of this kind will help determine to what extent uniquely human sociality and morality depend on other-regarding preferences emerging early in life.     

Could sexual selection have made us psychological altruists?

Psychological altruism (being motivated by the needs of others) has a tendency to produce behaviour that is costly in evolutionary terms. How, then, could the capacity for psychological altruism evolve? One suggestion is that it is the result of sexual selection. There are, however, two problems that face such an account: first, it is not clear that the resulting behaviour would be altruistic in the relevant sense, and second, it does not seem to fit with key features of our actual helping behaviour. I will argue that both of these problems can be avoided if we adopt a modular account of desire formation.     

Recipients affect prosocial and altruistic choices in jackdaws, Corvus monedula

Other-regarding preferences are a critical feature of human cooperation but to what extent non-human animals exhibit these preferences is a matter of intense discussion. We tested whether jackdaws show prosocial behaviour (providing benefits to others at no cost to themselves) and altruism (providing benefits to others while incurring costs) with both sibling and non-sibling recipients. In the prosocial condition, a box was baited on both the actor's and the recipient's side (1/1 option), whereas another box provided food only for the actor (1/0 option). In the altruistic condition, the boxes contained food for either the actor (1/0 option) or the recipient (0/1 option). The proportion of selfish (1/0 option) and cooperative (1/1 and 0/1 option, respectively) actors' choices was significantly affected by the recipients' behaviour. If recipients approached the boxes first and positioned themselves next to the box baited on their side, trying to access the food reward (recipient-first trials), actors were significantly more cooperative than when the actors approached the boxes first and made their choice prior to the recipients' arrival (actor-first trials). Further, in recipient-first trials actors were more cooperative towards recipients of the opposite sex, an effect that was even more pronounced in the altruistic condition. Hence, at no cost to the actors, all recipients could significantly influence the actors' behaviour, whereas at high costs this could be achieved even more so by recipients of different sex. Local/stimulus enhancement is discussed as the most likely cognitive mechanism to account for these effects.     

The evolution of reciprocal sharing

Genetical models of the evolution of reciprocal altruism (as distinct from cooperation, mutualism, or nepotism) have difficulty explaining the initial establishment of an altruist gene in a selfish deme. Though potential mechanisms have been suggested, there is an alternative: much “altruistic” behavior may in fact be purely selfish in origin and consequently reciprocity need not be invoked to provide a selective benefit to the actor. Sharing and helping are fundamentally different behavior categories and should not be confused. Patterns of resource sharing in chimpanzees correspond to predictions made by a selfish model but not to those of a reciprocal altruism model, and many observations of human gift exchange are consistent with the selfish, but not the altruistic, model. This suggests that presumed hominid meat exchange may have been the result of competition, not altruism or even cooperation, and that evolutionary models of “altruistic” behavior should be treated with caution.     

Chimpanzees Help Each Other upon Request

Background

The evolution of altruism has been explained mainly from ultimate perspectives. However, it remains to be investigated from a proximate point of view how and in which situations such social propensity is achieved. We investigated chimpanzees'' targeted helping in a tool transfer paradigm, and discuss the similarities and differences in altruism between humans and chimpanzees. Previously it has been suggested that chimpanzees help human experimenters by retrieving an object which the experimenter is trying to reach. In the present study, we investigated the importance of communicative interactions between chimpanzees themselves and the influence of conspecific partner''s request on chimpanzees'' targeted helping.

Methodology/Principal Findings

We presented two tool-use situations (a stick-use situation and a straw-use situation) in two adjacent booths, and supplied non-corresponding tools to paired chimpanzees in the two booths. For example, a chimpanzee in the stick-use situation was supplied with a straw, and the partner in the straw-use situation possessed a stick. Spontaneous tool transfer was observed between paired chimpanzees. The tool transfer events occurred predominantly following recipients'' request. Even without any hope of reciprocation from the partner, the chimpanzees continued to help the partner as long as the partner required help.

Conclusions/Significance

These results provide further evidence for altruistic helping in chimpanzees in the absence of direct personal gain or even immediate reciprocation. Our findings additionally highlight the importance of request as a proximate mechanism motivating prosocial behavior in chimpanzees whether between kin or non-kin individuals and the possible confounding effect of dominance on the symmetry of such interactions. Finally, in contrast to humans, our study suggests that chimpanzees rarely perform acts of voluntary altruism. Voluntary altruism in chimpanzees is not necessarily prompted by simple observation of another''s struggle to attain a goal and therefore an accurate understanding of others'' desires in the absence of communicative signals.     

Genetic differentiation and the evolution of cooperation in chimpanzees and humans

It has been proposed that human cooperation is unique among animals for its scale and complexity, its altruistic nature and its occurrence among large groups of individuals that are not closely related or are even strangers. One potential solution to this puzzle is that the unique aspects of human cooperation evolved as a result of high levels of lethal competition (i.e. warfare) between genetically differentiated groups. Although between-group migration would seem to make this scenario unlikely, the plausibility of the between-group competition model has recently been supported by analyses using estimates of genetic differentiation derived from contemporary human groups hypothesized to be representative of those that existed during the time period when human cooperation evolved. Here, we examine levels of between-group genetic differentiation in a large sample of contemporary human groups selected to overcome some of the problems with earlier estimates, and compare them with those of chimpanzees. We find that our estimates of between-group genetic differentiation in contemporary humans are lower than those used in previous tests, and not higher than those of chimpanzees. Because levels of between-group competition in contemporary humans and chimpanzees are also similar, these findings suggest that the identification of other factors that differ between chimpanzees and humans may be needed to provide a compelling explanation of why humans, but not chimpanzees, display the unique features of human cooperation.     

Tokens improve capuchin performance in the reverse–reward contingency task

In humans and apes, one of the most adaptive functions of symbols is to inhibit strong behavioural predispositions. However, to our knowledge, no study has yet investigated whether using symbols provides some advantage to non-ape primates. We aimed to trace the evolutionary roots of symbolic competence by examining whether tokens improve performance in the reverse–reward contingency task in capuchin monkeys, which diverged from the human lineage approximately 35 Ma. Eight capuchins chose between: (i) two food quantities, (ii) two quantities of ‘low-symbolic distance tokens’ (each corresponding to one unit of food), and (iii) two ‘high-symbolic distance tokens’ (each corresponding to a different amount of food). In all conditions, subjects had to select the smaller quantity to obtain the larger reward. No procedural modifications were employed. Tokens did improve performance: five subjects succeeded with high-symbolic distance tokens, though only one succeeded with food, and none succeeded with low-symbolic distance tokens. Moreover, two of the five subjects transferred the rule to novel token combinations. Learning effects or preference reversals could not account for the successful performance with high-symbolic distance tokens. This is, to our knowledge, the first demonstration that tokens do allow monkeys to inhibit strong behavioural predispositions, as occurs in chimpanzees and children.     

Capuchin monkeys (Cebus apella) fail to show inequality aversion in a no-cost situation

Although humans show robust equality concerns across a variety of situations, there is ongoing debate regarding the extent to which any nonhuman species is inequality averse. In the current research, we test nonhuman primates' reactions to conspecifics receiving equal and unequal payoffs using a “no-cost” method in which subjects can respond to inequality without rejecting food. Specifically, we gave capuchin monkeys (Cebus apella) the opportunity to trade with one of two experimenters, each of whom offered the subject an identical reward, but had different histories of trading with the subject and a conspecific partner. An “equal” experimenter had previously given a conspecific the same reward that the subject had received, whereas the other experimenter was either an “advantageous trader” for the subject (giving the conspecific an inferior reward) or a “disadvantageous trader” for the subject (giving the conspecific a superior reward). By offering subjects a choice between experimenters, we removed several competing demands that may have masked the expression of robust equality preferences in previous studies. Even though there was no cost associated with expressing an equality preference, we found no evidence that capuchins differentiated between equal and unequal experimenters.     

Dogs (Canis familiaris), but not chimpanzees (Pan troglodytes), understand imperative pointing

Chimpanzees routinely follow the gaze of humans to outside targets. However, in most studies using object choice they fail to use communicative gestures (e.g. pointing) to find hidden food. Chimpanzees' failure to do this may be due to several difficulties with this paradigm. They may, for example, misinterpret the gesture as referring to the opaque cup instead of the hidden food. Or perhaps they do not understand informative communicative intentions. In contrast, dogs seem to be skilful in using human communicative cues in the context of finding food, but as of yet there is not much data showing whether they also use pointing in the context of finding non-food objects. Here we directly compare chimpanzees' (N = 20) and dogs' (N = 32) skills in using a communicative gesture directed at a visible object out of reach of the human but within reach of the subject. Pairs of objects were placed in view of and behind the subjects. The task was to retrieve the object the experimenter wanted. To indicate which one she desired, the experimenter pointed imperatively to it and directly rewarded the subject for handing over the correct one. While dogs performed well on this task, chimpanzees failed to identify the referent. Implications for great apes' and dogs' understanding of human communicative intentions are discussed.     

Impact of internal and external factors on prosocial choices in rhesus macaques

While traditional economic models assume that agents are self-interested, humans and most non-human primates are social species. Therefore, many of decisions they make require the integration of information about other social agents. This study asks to what extent information about social status and the social context in which decisions are taken impact on reward-guided decisions in rhesus macaques. We tested 12 monkeys of varying dominance status in several experimental versions of a two-choice task in which reward could be delivered to self only, only another monkey, both the self and another monkey, or neither. Results showed dominant animals were more prone to make prosocial choices than subordinates, but only when the decision was between a reward for self only and a reward for both self and other. If the choice was between a reward for self only and a reward for other only, no animal expressed altruistic behaviour. Finally, prosocial choices were true social decisions as they were strikingly reduced when the social partner was replaced by a non-social object. These results showed that as in humans, rhesus macaques'' social decisions are adaptive and modulated by social status and the cost associated with being prosocial.This article is part of the theme issue ‘Existence and prevalence of economic behaviours among non-human primates’.     

<Emphasis Type="Italic">Cebus apella</Emphasis> Tolerate Intermittent Unreliability in Human Experimenters

Monkeys form expectations for outcomes based on interactions with human experimenters. Capuchins, a cooperative New World monkey species, not only anticipate receiving rewards that the experimenter indicates, but also apparently anticipate rewards based on what the experimenter has given to their partners. However, this could be due to subjects responding to either outcomes or experimenters. Here we examine whether capuchins will continue to interact with human experimenters who are occasionally unreliable. We tested 10 monkeys with a series of familiar human experimenters using an exchange task. The experimenters had never before participated in exchange studies with these monkeys, hence the monkeys learned about their behavior during the course of testing. Occasionally experimenters were unreliable, failing to give a reward after the monkey returned the token. The monkeys did recognize these interactions as different, responding much more quickly in trials following those that were nonrewarded than in other situations with the same experimenter. However, subjects did not change their preference for experimenters when given the opportunity to choose between the unreliable exchanger and another exchanger, nor did subjects learn to prefer reliable experimenters from watching other monkeys’ interactions. Instead, subjects returned the tokens to the same location from which they received it. These results indicate that capuchins may not be sensitive to isolated instances in which experimenters are unreliable, possibly because of a strong bias to returning the token to the location from which it was donated.     

Chimpanzee vocal signaling points to a multimodal origin of human language

The evolutionary origin of human language and its neurobiological foundations has long been the object of intense scientific debate. Although a number of theories have been proposed, one particularly contentious model suggests that human language evolved from a manual gestural communication system in a common ape-human ancestor. Consistent with a gestural origins theory are data indicating that chimpanzees intentionally and referentially communicate via manual gestures, and the production of manual gestures, in conjunction with vocalizations, activates the chimpanzee Broca's area homologue--a region in the human brain that is critical for the planning and execution of language. However, it is not known if this activity observed in the chimpanzee Broca's area is the result of the chimpanzees producing manual communicative gestures, communicative sounds, or both. This information is critical for evaluating the theory that human language evolved from a strictly manual gestural system. To this end, we used positron emission tomography (PET) to examine the neural metabolic activity in the chimpanzee brain. We collected PET data in 4 subjects, all of whom produced manual communicative gestures. However, 2 of these subjects also produced so-called attention-getting vocalizations directed towards a human experimenter. Interestingly, only the two subjects that produced these attention-getting sounds showed greater mean metabolic activity in the Broca's area homologue as compared to a baseline scan. The two subjects that did not produce attention-getting sounds did not. These data contradict an exclusive "gestural origins" theory for they suggest that it is vocal signaling that selectively activates the Broca's area homologue in chimpanzees. In other words, the activity observed in the Broca's area homologue reflects the production of vocal signals by the chimpanzees, suggesting that this critical human language region was involved in vocal signaling in the common ancestor of both modern humans and chimpanzees.     

Macaques (Macaca nemestrina) recognize when they are being imitated

This study investigated whether monkeys recognize when a human experimenter imitates their actions towards an object. Two experimenters faced 10 pigtailed macaques, who were given access to an interesting object. One experimenter imitated the monkeys' object-directed actions, the other performed temporally contingent but structurally different object-directed actions. Results show a significant visual preference for the imitator during manual object manipulations, but not mouthing actions. We argue that the ability to match actions could be based on both visual-visual and kinaesthetic-visual matching skills, and that mirror neurons, which have both visual and motor properties, could serve as a neural basis for recognizing imitation. However, imitation recognition as assessed by visual preference does not necessarily imply the capacity to attribute imitative intentionality to the imitator. The monkeys might implicitly recognize when they are being imitated without deeper insight into the mental processes of others.     

Does dishonesty really invite third-party punishment? Results of a more stringent test

Many experiments have demonstrated that people are willing to incur cost to punish norm violators even when they are not directly harmed by the violation. Such altruistic third-party punishment is often considered an evolutionary underpinning of large-scale human cooperation. However, some scholars argue that previously demonstrated altruistic third-party punishment against fairness-norm violations may be an experimental artefact. For example, envy-driven retaliatory behaviour (i.e. spite) towards better-off unfair game players may be misidentified as altruistic punishment. Indeed, a recent experiment demonstrated that participants ceased to inflict third-party punishment against an unfair player once a series of key methodological problems were systematically controlled for. Noticing that a previous finding regarding apparently altruistic third-party punishment against honesty-norm violations may have been subject to methodological issues, we used a different and what we consider to be a more sound design to evaluate these findings. Third-party punishment against dishonest players withstood this more stringent test.     

Altruism and Reward: Motivational Compatibility in Deceased Organ Donation

Acts of helping others are often based on mixed motivations. Based on this claim, it has been argued that the use of a financial reward to incentivize organ donation is compatible with promoting altruism in organ donation. In its report Human Bodies: Donation for Medicine and Research, the Nuffield Council on Bioethics uses this argument to justify its suggestion to pilot a funeral payment scheme to incentivize people to register for deceased organ donation in the UK. In this article, I cast a sceptical eye on the above Nuffield report's argument that its proposed funeral payment scheme would prompt deceased organ donations that remain altruistic (as defined by and valued the report). Specifically, I illustrate how this scheme may prompt various forms of mixed motivations which would not satisfy the report's definition of altruism. Insofar as the scheme produces an expectation of the reward, it stands diametrical to promoting an ‘altruistic perspective’. My minimal goal in this article is to argue that altruism is not motivationally compatible with reward as an incentive for donation. My broader goal is to argue that if a financial reward is used to incentivize organ donation, then we should recognize that the donation system is no longer aiming to promote altruism. Rewarded donation would not be altruistic but it may be ethical given a persistent organ shortage situation.