Why are bystanders friendly to recipients of aggression?

Figures & data

Table 1 Species in which post-conflict affiliation directed from a bystander to the recipient of aggression has been demonstrated and the suggested function of such interactions

Species	Location	Suggested function†
Pan troglodytes	Chester Zoo20,47	Stress reduction
	Arnhem Zoo19,66,68	Self-protection
	Taï Forest16,67	Relationship repair
	Mahale17
	ZooParc de Beauval18	Reduces social stress and aggression in entire group
	Yerkes Regional Primate Research Center34	Stress reduction
Pan paniscus	Apenheul Primate Park23	Stress reduction
Gorilla gorilla beringei	Zoo Atlanta22
	Apenheul Primate Park21	Stress reduction
Macaca arctoides	Yerkes Regional Primate Research Center25	Self-protection
Papio hamadryas ursinus ‡	Moremi Game Reserve, Botswana24	Relationship repair
Canis domesticus	Versele-Laga, Deinze, Belgium26
Corvus frugilegus *	University of Cambridge27	Strengthen partner bonds

† Functions are in italics if they were tested in the study. Cells are empty for cases where no function was suggested.

‡ The occurrence of bystander affiliation was not demonstrated but experimentally manipulated bystander affiliation was shown to increase tolerance between opponents to baseline levels.

* The occurrence of bystander initiated post-conflict affiliation with the recipient of aggression was demonstrated, but affiliation initiated by the recipient of aggression and initiated by the bystander were combined for analyses on the patterns of bystander affiliation and thus conclusions about the likely function refer to bystander affiliation initiated by either party.

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