Both humans and group-living animals associate and behave affiliatively more with some individuals than others. Human friendship has long been acknowledged, and recently scientists studying animal behaviour have started using the term friendship for close social associates in animals. Yet, while biologists describe friends as social tools to enhance fitness, social scientists describe human friendship as unconditional. We investigate whether these different descriptions reflect true differences in human friendship and animal close social associations or are a by-product of different research approaches: namely social scientists focussing on proximate and biologists on ultimate explanations. We first stress the importance of similar measures to determine close social associations, thereafter examine their ultimate benefits and proximate motivations, and discuss the latest findings on the central-neural regulation of social bonds. We conclude that both human friendship and animal close social associations are ultimately beneficial. On the proximate level, motivations for friendship in humans and for close social associations in animals are not necessarily based on benefits and are often unconditional. Moreover, humans share with many animals a similar physiological basis of sociality. Therefore, biologists and social scientist describe the same phenomenon, and the use of the term friendship for animals seems justified.

Cooperative decision rules have so far been shown experimentally mainly in mammal species that have variable and complex social networks. However, these traits should not necessarily be restricted to mammals. Therefore, we tested cooperative problem solving in ravens. We showed that, without training, nine ravens spontaneously cooperated in a loose-string task. Corroborating findings in several species, ravens’ cooperative success increased with increasing inter-individual tolerance levels. Importantly, we found this in both a forced dyadic setting and in a group setting where individuals had an open choice to cooperate with whomever. The ravens, moreover, also paid attention to the resulting reward distribution and ceased cooperation when being cheated upon. Nevertheless, the ravens did not seem to pay attention to the behavior of their partners while cooperating and future research should reveal whether this is task specific or a general pattern. Given their natural propensity to cooperate and the results we present here, we consider ravens as an interesting model species to study the evolution of and the mechanisms underlying cooperation.

A core feature of social intelligence is the understanding of third-party relations, which has been experimentally demonstrated in primates. Whether other social animals also have this capacity, and whether they can use this capacity flexibly to, for example, also assess the relations of neighbouring conspecifics, remains unknown. Here we show that ravens react differently to playbacks of dominance interactions that either confirm or violate the current rank hierarchy of members in their own social group and of ravens in a neighbouring group. Therefore, ravens understand third-party relations and may deduce those not only via physical interactions but also by observation.

Various studies and researchers have proposed a link between contagious yawning and empathy, yet the conceptual basis for the proposed connection is not clear and deserves critical evaluation. Therefore, we systematically examined the available empirical evidence addressing this association; i.e., a critical review of studies on inter-individual differences in contagion and self-reported values of empathy, differences in contagion based on familiarity or sex, and differences in contagion among individuals with psychological disorders, as well as developmental research, and brain imaging and neurophysiological studies. In doing so, we reveal a pattern of inconsistent and inconclusive evidence regarding the connection between contagious yawning and empathy. Furthermore, we identify study limitations and confounding variables, such as visual attention and social inhibition. Future research examining links between contagious yawning and empathy requires more rigorous investigation involving objective measurements to explicitly test for this connection.

The competition for power in a complex social world is hypothesized to be a driving force in the evolution of intelligence. More specifically, power may be obtained not only by brute force but also by social strategies resembling human politics. Most empirical evidence comes from primate studies that report unprovoked aggression by dominants to maintain power by spreading fear and third-party interventions in conflicts. Coalitionary support has also been described in other animals and is often linked to social bonding. As coalitions can lead to a gain in power and fitness benefits, individuals may try to prevent coalitionary support or indirectly prevent others from forming social bonds that might lead to coalitions. Although there is some empirical evidence that coalitionary support can be manipulated, little is known about the indirect strategy. We show here that wild ravens (Corvus corax) regularly intervene in affiliative interactions of others even though such interventions are potentially risky and without immediate benefits. Moreover, the identities of both interveners and intervened pairs are not randomly distributed. Ravens with existing ties initiate most interventions, and ravens that are creating new ties are most likely to be the targets of interventions. These patterns are consistent with the idea that interventions function to prevent others from forming alliances and consequently becoming future competitors. We thus show previously undescribed social maneuvers in the struggle for power. These maneuvers are likely to be of importance in other social species as well.