When is bigger better? The effects of group size on the evolution of helping behaviours.

Understanding the evolution of sociality in humans and other species requires understanding how selection on social behaviour varies with group size. However, the effects of group size are frequently obscured in the theoretical literature, which often makes assumptions that are at odds with empirical findings. In particular, mechanisms are suggested as supporting large-scale cooperation when they would in fact rapidly become ineffective with increasing group size. Here we review the literature on the evolution of helping behaviours (cooperation and altruism), and frame it using a simple synthetic model that allows us to delineate how the three main components of the selection pressure on helping must vary with increasing group size. The first component is the marginal benefit of helping to group members, which determines both direct fitness benefits to the actor and indirect fitness benefits to recipients. While this is often assumed to be independent of group size, marginal benefits are in practice likely to be maximal at intermediate group sizes for many types of collective action problems, and will eventually become very small in large groups due to the law of decreasing returns. The second component is the response of social partners on the past play of an actor, which underlies conditional behaviour under repeated social interactions. We argue that under realistic conditions on the transmission of information in a population, this response on past play decreases rapidly with increasing group size so that reciprocity alone (whether direct, indirect, or generalised) cannot sustain cooperation in very large groups. The final component is the relatedness between actor and recipient, which, according to the rules of inheritance, again decreases rapidly with increasing group size. These results explain why helping behaviours in very large social groups are limited to cases where the number of reproducing individuals is small, as in social insects, or where there are social institutions that can promote (possibly through sanctioning) large-scale cooperation, as in human societies. Finally, we discuss how individually devised institutions can foster the transition from small-scale to large-scale cooperative groups in human evolution.

Understanding bystanders’ willingness to Intervene in traditional and cyberbullying scenarios.

Bullying incidents in traditional and online settings are a cause for concern to many parties. The goal of the current study was to explore the extent to which a bystander would intervene in a bullying incident and the degree to which this behavior is influenced by group size (the number of other witnesses), the setting (traditional or cyberbullying), and gender of the victim. Using an online survey method, participants were presented with eight bullying scenarios, each of which involved verbal bullying of a victim. Participants (N = 82) were asked to report how likely they would be to intervene in each of these scenarios. Results showed that female victims were more likely to be helped than male victims. Furthermore, female participants were more willing to intervene than the male participants in the cyberbullying scenarios. Altruism was a positive predictor of participants’ willingness to intervene. The present findings suggest that certain gender differences in helping behavior may depend on the context in which bullying is observed (traditional or cyberbullying).