Humans regularly provide others with resources at a personal cost to themselves. Chimpanzees engage in some cooperative behaviors in the wild as well, but their motivational underpinnings are unclear. In three experiments, chimpanzees (Pan troglodytes) always chose between an option delivering food both to themselves and a partner and one delivering food only to themselves. In one condition, a conspecific partner had just previously taken a personal risk to make this choice available. In another condition, no assistance from the partner preceded the subject’s decision. Chimpanzees made significantly more prosocial choices after receiving their partner’s assistance than when no assistance was given (experiment 1) and, crucially, this was the case even when choosing the prosocial option was materially costly for the subject (experiment 2). Moreover, subjects appeared sensitive to the risk of their partner’s assistance and chose prosocially more often when their partner risked losing food by helping (experiment 3). These findings demonstrate experimentally that chimpanzees are willing to incur a material cost to deliver rewards to a conspecific, but only if that conspecific previously assisted them, and particularly when this assistance was risky. Some key motivations involved in human cooperation thus may have deeper phylogenetic roots than previously suspected

Numerous studies have investigated children's abilities to attribute mental states, but few have examined their ability to recruit these abilities in social interactions. Here, 6-year-olds (N = 104) were tested on whether they can use first-and second-order false-belief understanding to coordinate with peers. Children adjusted their decisions in a coordination game in response to either their partner's erroneous belief or their partner's erroneous belief about their own belief-a result that contrasts with previous findings on the use of higher order "theory of mind" (TOM) reasoning at this age. Six-year-olds are thus able to use their higher order TOM capacities for peer coordination, which marks an important achievement in becoming competent social collaborators.

Humans constantly have to coordinate their decisions with others even when their interests are conflicting (e.g., when 2 drivers have to decide who yields at an intersection). So far, however, little is known about the development of these abilities. Here, we present dyads of 5-year-olds (N ϭ 40) with a repeated chicken game using a novel methodology: Two children each steered an automated toy train carrying a reward. The trains simultaneously moved toward each other so that in order to avoid a crash-which left both children empty-handed-1 train had to swerve. By swerving, however, the trains lost a portion of the rewards so that it was in each child's interest to go straight. Children coordinated their decisions successfully over multiple rounds, and they mostly did so by taking turns at swerving. In dyads in which turn-taking was rare, dominant children obtained significantly higher payoffs than their partners. Moreover, the coordination process was more efficient in turn-taking dyads as indicated by a significant reduction in conflicts and verbal protest. These findings indicate that already by the late preschool years children can independently coordinate decisions with peers in recurrent conflicts of interest.Keywords: coordination, cooperation, conflict, compromise, turn-taking, dominanceHumans are highly successful at coordinating their decisions with others when pursuing shared interests (Bicchieri, 2006;Tomasello, 2014). However, a central challenge of human social functioning is that people often have to coordinate even in social dilemmas in which their interests are conflicting, for example, when one of two drivers has to yield at an intersection or when deciding who has to do an undesirable part of a joint work project. What these situations have in common is that each individual prefers someone else to incur the cost of behaving cooperatively but everyone is worse off if no one volunteers to cooperate (commonly modeled as "volunteer's dilemmas" or "chicken games" in game theory; see Archetti, 2009;Rapoport & Chammah, 1966). In large modern societies these situations are often resolved through collectively agreed upon coordination rules grounded in our culturally shared normative understanding (e.g., standing in line at supermarket checkouts) and sometimes formulated in formal laws (e.g., traffic rules).In repeated dyadic interactions, however, such explicit rules often do not exist and people are frequently required to generate solutions independently, for example, when two spouses have to decide who picks up the kids from school. One solution to dyadic conflict-of-interest coordination problems is to take turns at behaving cooperatively as this ensures that the interaction is mutually profitable in the long run. Indeed, turn-taking is commonly used in natural settings, as shown, for example, by ethnographic analyses of fishermen taking turns at fishing in preferred spots (Berkes, 1986), or anecdotal evidence of soldiers taking turns at assuming the most exposed position in a combat military formati...

Humans are routinely required to coordinate with others. When communication is not possible, adults often achieve this by using salient cues in the environment (e.g. going to the Eiffel Tower, as an obvious meeting point). To explore the development of this capacity, we presented dyads of 3-, 5-, and 8-year-olds (N = 144) with a coordination problem: Two balls had to be inserted into the same of four boxes to obtain a reward. Identical pictures were attached to three boxes whereas a unique -and thus salient -picture was attached to the fourth. Children either received one ball each, and so had to choose the same box (experimental condition), or they received both balls and could get the reward independently (control condition). In all cases, children could neither communicate nor see each other's choices. Children were significantly more likely to choose the salient option in the experimental condition than in the control condition. However, only the two older age groups chose the salient box above chance levels. This study is the first to show that children from at least age 5 can solve coordination problems by converging on a salient solution. Research highlights• Dyads of children (3-, 5-, and 8-year-olds) were presented with a coordination problem where they had to choose the same of four options as their partner to be rewarded.

To cooperate effectively, both in small-scale interactions and large-scale collective-action problems, people frequently have to delay gratification (i.e., resist short-term temptations in favor of joint long-term goals). Although delay-of-gratification skills are commonly considered critical in children’s social-cognitive development, they have rarely been studied in the context of cooperative decision-making. In the current study, we therefore presented pairs of children ( N = 207 individuals) with a modified version of the famous marshmallow test, in which children’s outcomes were interdependently linked such that the children were rewarded only if both members of the pair delayed gratification. Children from two highly diverse cultures (Germany and Kenya) performed substantially better than they did on a standard version of the test, suggesting that children are more willing to delay gratification for cooperative than for individual goals. The results indicate that from early in life, human children are psychologically equipped to respond to social interdependencies in ways that facilitate cooperative success.