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.

Feeding competition is thought to play a role in primate social organization as well as cognitive evolution. For chimpanzees (Pan troglodytes), social and ecological factors can affect competition, yet how these factors interact to affect feeding behavior is not fully understood; they can be difficult to disentangle in wild settings. This experiment investigated the differential effects of food quantity, the presence of a co-feeding partner, and the contestability of a food patch on feeding rate. We presented tolerant pairs of chimpanzees from a semi-captive social group with an apparatus comprising a matrix of transparent tubes between two adjacent rooms, of which, either all (abundant condition) or only a small proportion (scarce condition) were baited with peanuts. Dyads were either grouped into the competitive treatment, in which peanuts were accessible from both sides of the apparatus simultaneously, or the non-competitive treatment, in which the peanuts were pre-divided; half of the tubes were accessible to one chimpanzee from one side, and the other half were accessible only from the opposite side of the apparatus. We compared dyadic tolerance levels with individual feeding rates across quantity conditions and between competitive treatments. While tolerance and food quantity had no effect on feeding rate, partner presence significantly increased feeding rate relative to individual feeding. This increase was much larger when the dyads directly competed over the peanuts than when they were co-feeding on a pre-divided set of peanuts. Thus, in a co-feeding situation, the presence of another individual and, to an even larger extent, the contestability of the food source play a larger role in chimpanzee feeding behavior than dyadic tolerance or food quantity. These findings highlight the relative impact of social facilitation and direct competition on co-feeding behavior between pairs of chimpanzees.

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Competition over common-pool resources (CPR) is a ubiquitous challenge for social animals. Many species face similar dilemmas, yet our understanding of the evolutionary trajectory of CPR social strategies remains unexplored. Here, we provide a first look at the social strategies of our closest living relatives, chimpanzees (Pan troglodytes), in two novel resource dilemma experiments. Dyads of chimpanzees were presented with renewable resource systems, collapsible at a quantity-dependent threshold. Dyads had to continuously resist overconsumption to maximize collective gains. In study 1, dyads of chimpanzees sustained a renewing juice source. Inequality of juice acquisition between partners predicted sustaining success, indicating that one individual dominated the task while the partner inhibited. Dyads in study 2 fed together on accumulating carrot pieces but could end the accumulation any time by grabbing an immediate selfish source of carrots. Dyads with low tolerance were more successful at collectively sustaining the resource than highly tolerant dyads. Further, the dominant individual was more likely to cause collapse in dyads with low tolerance than dyads with high tolerance. These results indicate that chimpanzees use a dominance-based monopolisation strategy moderated by social tolerance to overcome the tragedy of the commons.

Sexual desire, physical activity, economic choices and other behaviours fluctuate over the menstrual cycle. However, we have an incomplete understanding of how preferences for smaller sooner or larger later rewards (known as delay discounting) change over the menstrual cycle. In this pre-registered, cross-sectional study, Bayesian linear and quadratic binomial regression analyses provide compelling evidence that delay discounting does change over the menstrual cycle. Data from 203 naturally cycling women show increased discounting (preference for more immediate rewards) mid-cycle, which is at least partially driven by changes in fertility. This study provides evidence for a robust and broad-spectrum increase in delay discounting (Cohen’s h ranging from 0.1 to 0.4) around the fertile point in the menstrual cycle across multiple commodities (money, food, and sex). We also show, for the first time, that discounting changes over the menstrual cycle in a pseudo-control group of 99 women on hormonal contraception. Interestingly, such women increase their discounting of sex toward the end of the menstrual phase — possibly reflecting a prioritisation of bonding-related sexual activity before menstrual onset.