Intergroup competition makes social identity salient, which in turn affects how people respond to competitors' hardships. The failures of an in-group member are painful, whereas those of a rival out-group member may give pleasure-a feeling that may motivate harming rivals. The present study examined whether valuation-related neural responses to rival groups' failures correlate with likelihood o...

Many animals use signals to assess the fighting ability of rivals and reduce the cost of aggressive competition. However, little is known about how an individual's own quality influences their signal assessment decisions. Polistes dominulus wasps have visual signals of fighting ability that provide a good model for testing the dynamics of rival choice. We found that rival assessment behaviour w...

When females are sexually promiscuous, the intensity of sperm competition for males depends on how many partners females mate with. To maximize fitness, males should adjust their copulatory investment in relation to this intensity. However, fitness costs associated with sperm competition may not only depend on how many males a female has mated with, but also how related rival males are. Accordi...