Close social associations in animals and humans: functions and mechanisms of friendship

Abstract

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.

Post-copulatory grooming: a conditional mating strategy?

“…Through repeated copulations, lactating females might still be successful in conceiving new offspring. On the other hand, females nursing offspring from the previous season may gain protection and social support (Palombit et al 1997;Palombit et al 2001;Lemasson et al 2008) from their male copulation partners and thus benefit from establishing stable, long-term social relations (usually established, maintained and repaired by social grooming) or 'friendships' with them (Massen et al 2010;Massen and Sterck 2013). Barbary macaque males show some care for infants, both to later gain mating access to the mother and to use infants as social tools for 'agonistic buffering' in conflicts with other males (Deag and Crook 1971;Small 1990a;Paul et al 1996;Ménard et al 2001).…”

Maternal kin bias in affiliative behavior among wild adult female blue monkeys

“…On an ultimate level, such biases may reflect the inclusive fitness benefits of targeting cooperative behavior toward relatives [Wrangham, 1982]. More proximately, the female philopatry that characterizes many mammals [Greenwood, 1980;Pusey & Packer, 1987] means that maternally related individuals live together over long periods, and familiarity among long-term co-residents may facilitate tolerance and cooperation [Chapais, 2001;Dunbar, 1988;Massen et al, 2010]. Strong, enduring social bonds may have substantial fitness consequences for those involved [Seyfarth & Cheney, 2012;Silk, 2007].…”

Pectoral fin contact as a mechanism for social bonding among dolphins

“…Close social associations lead to social bonding (Massen, Sterck, & de Vos, 2010), but understanding how these associations are established and managed among aquatic social mammals such as dolphins is still being clarified.…”

“…This method focuses on time spent together as opposed to examining the quality of the interaction (e.g., Kummer, 1978). Another way to examine social bonds between two specific individuals is by examining the exchange of affiliative behaviors as compared to other pairs within a group; exchanging a large number of affiliative behaviors would constitute a strong social bond (Massen et al, 2010). One well-studied example of affiliative behavior used by dolphins is sharing of pectoral fin contact (e.g., Dudzinski, Gregg, Ribic, & Kuczaj, 2009;Dudzinski, Gregg, Paulos, & Kuczaj, 2010;Dudzinski et al, 2012;Dudzinski, Danaher-Garcia, & Gregg, 2013;Johnson & Moewe, 1999;Mann & Smuts, 1998;Paulos, Dudzinski, & Kuczaj, 2007;Sakai, Takeda, & Kohshima, 2006a, b).…”