Chimpanzees are more likely to play or to take care of one another if they see others performing these social behaviours first, report Georgia Sandars and colleagues from Durham University, in the United Kingdom, in a study published in the open-access journal PLOS ONE.
Whether yawning or being alert to predators, many animals — including primates and crows — consider certain behaviours contagious: after seeing another member of their group perform one of these behaviours, they instinctively do so themselves.
It is thought that this “behavioural contagion” helps animal groups reinforce their social bonds and stay synchronized. The behaviour and emotions of chimpanzees can be influenced by the humans around them, but it has not yet been investigated whether these animals are contagiously influenced by friendly social behaviours, such as grooming and play.
To fill this knowledge gap, the researchers observed the behaviour of 41 chimpanzees living in a sanctuary in Zambia. They found that chimpanzees of all ages, categories and sexes displayed contagion of grooming and play behaviours.
Chimpanzees were more likely to perceive grooming behaviour as contagious when observed in another individual with whom they had a close relationship. By contrast, playful behaviour was more contagious in younger chimpanzees, but this contagion was not affected by the strength of the social bond.
The behavioural contagion of friendly behaviours, such as grooming and play, may help reinforce social bonds, the authors say. Play is an important part of the social and behavioural development of young chimpanzees, while adults tend to build and repair social relationships through mutual grooming, which may explain the differences in contagion between the two behaviours.
There are several possible explanations for why adult chimpanzees consider the behaviour of individuals with whom they have a close social relationship to be more contagious: they may pay more attention or be more strongly influenced by their close friends, or seeing a close friend caring for another person may trigger jealousy.
The authors add: “Chimpanzees ‘catch’ social behaviour from one another; it is more likely that they will start brushing their teeth and playing after having seen others brushing their teeth and playing.”
