Alicia P. Melis

Chimpanzees Recruit the Best Collaborators

Humans collaborate with non-kin in special ways, but the evolutionary foundations of these collaborative skills remain unclear. We presented chimpanzees with collaboration problems in which they had to decide when to recruit a partner and which potential partner to recruit. In an initial study, individuals recruited a collaborator only when solving the problem required collaboration. In a second study, individuals recruited the more effective of two partners on the basis of their experience with each of them on a previous day. Therefore, recognizing when collaboration is necessary and determining who is the best collaborative partner are skills shared by both chimpanzees and humans, so such skills may have been present in their common ancestor before humans evolved their own complex forms of collaboration.

Engineering cooperation in chimpanzees: tolerance constraints on cooperation

The cooperative abilities of captive chimpanzees, Pan troglodytes, in experiments do not match the sophistication that might be predicted based on their naturally occurring cooperative behaviours. This discrepancy might partly be because in previous experiments potential chimpanzee cooperators were partnered without regard to their social relationship. We investigated the ability of chimpanzee dyads to solve a physical task cooperatively in relation to their interindividual tolerance levels. Pairs that were most capable of sharing food outside the test were also able to cooperate spontaneously (by simultaneously pulling two ropes) to obtain food. In contrast, pairs that were less inclined to share food outside of the test were unlikely to cooperate. Furthermore, previously successful subjects stopped cooperating when paired with a less tolerant partner, even when the food rewards were presented in a dispersed and divisible form to reduce competition between subjects. These results show that although chimpanzees are capable of spontaneous cooperation in a novel instrumental task, tolerance acts as a constraint on their ability to solve such cooperative problems. This finding highlights the importance of controlling such social constraints in future experiments on chimpanzee cooperation, and suggests that the evolution of human-like cooperative skills might have been preceded by the evolution of a more egalitarian social system and a more human-like temperament.

Two key steps in the evolution of human cooperation: the interdependence hypothesis

Modern theories of the evolution of human cooperation focus mainly on altruism. In contrast, we propose that humans’ species-unique forms of cooperation—as well as their species-unique forms of cognition, communication, and social life—all derive from mutualistic collaboration (with social selection against cheaters). In a first step, humans became obligate collaborative foragers such that individuals were interdependent with one another and so had a direct interest in the well-being of their partners. In this context, they evolved new skills and motivations for collaboration not possessed by other great apes (joint intentionality), and they helped their potential partners (and avoided cheaters). In a second step, these new collaborative skills and motivations were scaled up to group life in general, as modern humans faced competition from other groups. As part of this new group-mindedness, they created cultural conventions, norms, and institutions (all characterized by collective intentionality), with knowledge of a specific set of these marking individuals as members of a particular cultural group. Human cognition and sociality thus became ever more collaborative and altruistic as human individuals became ever more interdependent.Modern theories of the evolution of human cooperation focus mainly on altruism. In contrast, we propose that humans’ species-unique forms of cooperation—as well as their species-unique forms of cognition, communication, and social life—all derive from mutualistic collaboration (with social selection against cheaters). In a first step, humans became obligate collaborative foragers such that individuals were interdependent with one another and so had a direct interest in the well-being of their partners. In this context, they evolved new skills and motivations for collaboration not possessed by other great apes (joint intentionality), and they helped their potential partners (and avoided cheaters). In a second step, these new collaborative skills and motivations were scaled up to group life in general, as modern humans faced competition from other groups. As part of this new group-mindedness, they created cultural conventions, norms, and institutions (all characterized by collective intentionality), with knowledge of a specific set of these marking individuals as members of a particular cultural group. Human cognition and sociality thus became ever more collaborative and altruistic as human individuals became ever more interdependent.

Chimpanzees (Pan troglodytes) Conceal Visual and Auditory Information From Others

Chimpanzees (Pan troglodytes) competed with a human for food. The human sat inside a booth, with 1 piece of food to her left and 1 to her right, which she could retract from her chimpanzee competitors reach as needed. In Experiment 1, chimpanzees could approach either side of the booth unseen but then had to reach through 1 of 2 tunnels (1 clear, 1 opaque) for the food. In Experiment 2, both tunnels were clear and the human was looking away, but 1 of the tunnels made a loud noise when it was opened. Chimpanzees preferentially reached through the opaque tunnel in the first study and the silent tunnel in the second, successfully concealing their taking of the food from the human competitor in both cases. These results suggest that chimpanzees can, in some circumstances, actively manipulate the visual and auditory perception of others by concealing information from them.

Young Children Share the Spoils After Collaboration

Egalitarian behavior is considered to be a species-typical component of human cooperation. Human adults tend to share resources equally, even if they have the opportunity to keep a larger portion for themselves. Recent experiments have suggested that this tendency emerges fairly late in human ontogeny, not before 6 or 7 years of age. Here we show that 3-year-old children share mostly equally with a peer after they have worked together actively to obtain rewards in a collaboration task, even when those rewards could easily be monopolized. These findings contrast with previous findings from a similar experiment with chimpanzees, who tended to monopolize resources whenever they could. The potentially species-unique tendency of humans to share equally emerges early in ontogeny, perhaps originating in collaborative interactions among peers.

Do chimpanzees reciprocate received favours

Reciprocal interactions observed in animals may persist because individuals keep careful account of services exchanged with each group member. To test whether chimpanzees, Pan troglodytes, possess the cognitive skills required for this type of contingency-based reciprocity, we gave chimpanzees the choice of cooperating with a conspecific who had helped them previously or one who had not helped them in two different experimental tasks. In the first experiment, one of the partners preferentially recruited the subjects to cooperate in a mutualistic task, while the other potential partner never chose to cooperate with the subject, but rather chose a different partner. In the second experiment, one of the partners altruistically helped the subjects to reach food, while the other partner never helped the subject, but rather took the food himself. In both experiments there was some evidence that the chimpanzees increased the amount they cooperated with or helped the partner who had been more helpful towards them compared to their baseline behaviour towards the same individual (or in a control condition). However, in both experiments this effect was relatively weak and subjects did not preferentially favour the individual who had favoured them over the one who had not in either experiment. Although taken together, these experiments provide some support for the hypothesis that chimpanzees are capable of contingent reciprocity, they also suggest that models of immediate reciprocation and detailed accounts of recent exchanges (e.g. Tit for Tat) may not play a large role in guiding the social decisions of chimpanzees.

Two Key Steps in the Evolution of Human Cooperation

Modern theories of the evolution of human cooperation focus mainly on altruism. In contrast, we propose that humans’ species-unique forms of cooperation—as well as their species-unique forms of cognition, communication, and social life—all derive from mutualistic collaboration (with social selection against cheaters). In a first step, humans became obligate collaborative foragers such that individuals were interdependent with one another and so had a direct interest in the well-being of their partners. In this context, they evolved new skills and motivations for collaboration not possessed by other great apes (joint intentionality), and they helped their potential partners (and avoided cheaters). In a second step, these new collaborative skills and motivations were scaled up to group life in general, as modern humans faced competition from other groups. As part of this new group-mindedness, they created cultural conventions, norms, and institutions (all characterized by collective intentionality), with knowledge of a specific set of these marking individuals as members of a particular cultural group. Human cognition and sociality thus became ever more collaborative and altruistic as human individuals became ever more interdependent.Modern theories of the evolution of human cooperation focus mainly on altruism. In contrast, we propose that humans’ species-unique forms of cooperation—as well as their species-unique forms of cognition, communication, and social life—all derive from mutualistic collaboration (with social selection against cheaters). In a first step, humans became obligate collaborative foragers such that individuals were interdependent with one another and so had a direct interest in the well-being of their partners. In this context, they evolved new skills and motivations for collaboration not possessed by other great apes (joint intentionality), and they helped their potential partners (and avoided cheaters). In a second step, these new collaborative skills and motivations were scaled up to group life in general, as modern humans faced competition from other groups. As part of this new group-mindedness, they created cultural conventions, norms, and institutions (all characterized by collective intentionality), with knowledge of a specific set of these marking individuals as members of a particular cultural group. Human cognition and sociality thus became ever more collaborative and altruistic as human individuals became ever more interdependent.

Coordination of Chimpanzees (Pan troglodytes) in a Stag Hunt Game

Group-living animals frequently face situations in which they must coordinate individual and sometimes conflicting goals. We assessed chimpanzees’ ability to coordinate in a Stag Hunt game. Dyads were confronted with a situation in which each individual was already foraging on a low-value food (hare) when a high-value food (stag) appeared that required collaboration for retrieval, with a solo attempt to get the stag resulting in a loss of both options. In one condition visibility between partners was open whereas in the other it was blocked by a barrier. Regardless of condition, dyads almost always (91%) coordinated to choose the higher valued collaborative option. Intentional communication or monitoring of the partner’s behavior before decision making—characteristic of much human coordination—were limited. Instead, all dyads adopted a leader–follower strategy in which one partner took the risk of going first, presumably predicting that this would induce the other to join in (sometimes communicating if she was slow to do so). These results show that humans’ closest primate relatives do not use complex communication to coordinate but most often use a less cognitively complex strategy that achieves the same end.

Chimpanzees, Pan troglodytes, prefer individual over collaborative strategies towards goals

Chimpanzees engage in a number of group activities, but it is still unclear to what extent they prefer mutualistic collaborative strategies over individual strategies to achieve their goals. In one experiment, we gave chimpanzees the choice between pulling a platform to within reach either individually or collaboratively with a tolerant partner, both strategies having equivalent payoffs. Overall, chimpanzees preferred the individual option, and this preference was independent of the type of reward for which they were working (food or tool). In a second experiment, chimpanzees switched to the collaboration option as soon as the payoff was increased for this option. These results suggest that chimpanzees prefer to work alone in foraging-like situations and choose collaboration only if it maximizes their reward. These results thus make a strong case for the hypothesis that differences between humans’ and chimpanzees’ collaboration are to a great extent due to motivational differences.

Dogs (Canis familiaris) Evaluate Humans on the Basis of Direct Experiences Only

Reputation formation is a key component in the social interactions of many animal species. An evaluation of reputation is drawn from two principal sources: direct experience of an individual and indirect experience from observing that individual interacting with a third party. In the current study we investigated whether dogs use direct and/or indirect experience to choose between two human interactants. In the first experiment, subjects had direct interaction either with a “nice” human (who played with, talked to and stroked the dog) or with an “ignoring” experimenter who ignored the dog completely. Results showed that the dogs stayed longer close to the “nice” human. In a second experiment the dogs observed a “nice” or “ignoring” human interacting with another dog. This indirect experience, however, did not lead to a preference between the two humans. These results suggest that the dogs in our study evaluated humans solely on the basis of direct experience.