The Evolution of Pro-social Concern

In an attempt to better understand evolution of altruism, there has been a recent surge in studies on pro-social behaviours like helping. Next to humans a variety of animals has been tested in experiments on pro-sociality, with however, rather inconsistent results within and between species and across context. This raises questions about the evolutionary pressures (e.g. aspects of social life) and motivations behind pro-social behaviour (e.g. need, sympathy). Therefore, the aim of the current proposal is two-fold: The first aim is to test two main hypotheses about the evolution of pro-social behaviour, namely the cooperative breeding hypothesis and the social bonding hypothesis, by making use of the comparative approach, including species with two distinct social features (cooperative breeding (CB) and social bonds (SB)). To control for effects of common ancestry, next to humans I will include two species per two phylogenetical different lineages (primates: common marmosets (CB) vs. long-tailed macaques (SB); and corvids: Iberian magpies (CB) vs. common ravens (SB)). The second aim of the proposal is to test underlying motivation of prosocial behaviour, by confronting all five species with a series of experiments that vary across necessity and costs of pro-social behaviour.

This project has shown that prosocial and cooperative behaviours have evolved independently in both primates and corvids, and that the degree of such behaviour in a species depends on the species social system and the specific context for which the behaviour is needed. The aim of this project was to test two main hypotheses about the evolution of prosocial behaviour, namely the cooperative breeding hypothesis and the social bonding hypothesis, by testing humans and species that portray either cooperative breeding (CB) or strong social bonds (SB), while looking at two completely different animal classes: primates (common marmosets (CB) vs. long-tailed macaques (SB)), and corvids (Azure-winged magpies (CB) vs. common ravens (SB)). First, we could show that even in a very competitive environment humans are as prosocial as commonly believed. Moreover, in series of experiments, we showed that in a paradigm comparable to those used for animals, human children are prosocial too, even when at a cost to themselves, and already at an early age (3-5yrs). In contrast, ravens failed to show other-regard in two different paradigms, although they did provide at a moderate level in a group service paradigm. Nevertheless, the cooperatively breeding Azure-winged magpies provided at much higher levels in the same group service paradigm and in fact took any chance they got to provide to their group. Additional testing on a range of other corvid species revealed that species that have territorial pair-bonds or breed in colonies, where least prosocial, and those that are facultative cooperative breeders where somewhere in between, providing some first qualitative proof for the cooperative breeding hypothesis in corvids. Moreover, we noticed that the motivations behind being prosocial also differed per species, with azure-winged magpies providing indiscriminately, whereas for example the ravens only provided to higher-ranking individuals. In contrast to their other regarding preferences, the ravens showed to be very proficient in a cooperation task, comparable to, for example chimpanzees. And both in the ravens, but also in kea, we found that particularly the social bond between two individuals predicts how well they will cooperate, and the ravens in fact choose to cooperate with their friends. In long-tailed macaques we could elucidate physiological mechanisms that may be responsible for such preferences; i.e., we could show that salivary cortisol levels of the macaques dropped when cooperating, yet only when cooperating with a friend, and thus cooperating with a friend may have a stress alleviating effect. Finally, in common marmosets, we brought together the studies on prosociality and cooperation, and showed that prosocial individuals are also more cooperative. In sum, by showing prosociality and its limits in different context in species ranging from primates to corvids, we have gained a better understanding of how prosociality evolved to the extraordinary levels we can witness in humans.