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Positive Emotional Contagion Fosters Friendliness in Monkeys

When female Barbary macaques observe others grooming, they become more relaxed.

Seeing is feeling: monkey see, monkey feel, monkey do

A recent essay by Michael Marshall in New Scientist magazine called "Monkeys chill out just from seeing their friends being groomed" caught my eye. It's only available to subscribers, but the original research article by Juliette Berthier and Stuart Semple about which Mr. Marshall is writing titled "Observing grooming promotes affiliation in Barbary macaques" is available for free and is a relatively easy read. These scientists write, "Observing friendly social interactions makes people feel good and, as a result, then act in an affiliative way towards others. Positive visual contagion of this kind is common in humans, but whether it occurs in non-human animals is unknown. We explored the impact on female Barbary macaques [Macaca silvanus] of observing grooming, a behaviour that physiological and behavioural studies indicate has a relaxing effect on the animals involved."

To learn more about the presence of positive visual contagion in these monkeys, 20 individually identified semi-free-ranging adult females comprising 154 pairs were observed at Trentham Monkey Forest (Stoke-on-Trent, UK). The researchers were specifically interested in testing the hypothesis that observing grooming leads to positive contagion. They note, "Such contagion could result in positive changes in affective state, promote grooming, increase rates of other affiliative behaviour, or inhibit agonistic behaviour; we explored predictions related to each of these four possibilities." (See note 1 for more details about their predictions.)

Female macaques display positive visual contagion

The researchers found the first example of positive visual contagion in nonhumans. They report, "seeing conspecifics groom was associated with a reduction in a behavioural indicator of anxiety among bystanders, suggesting that seeing others groom is, in itself, relaxing. In addition observation of grooming bouts was associated with increases in a range of affiliative behaviours, including grooming itself. These findings provide evidence from a non-human species that observing affiliative interactions of conspecifics can lead to positive contagion. This work further highlights the importance of exploring animal social behaviour not just at the level of the interacting individuals, but also within the broader social environment in which the behaviour occurs." It's also interesting to ponder the possible role of mirror neurons when various emotional states are shared among members of a social group.

Emotional contagion among dogs at play: Go to the dogs and take a bow

I look forward to more studies like this on other nonhuman primates and nonhumans representing different taxa. It would be surprising to learn that positive visual contagion is limited to these monkeys or only to other nonhuman primates, but we really don't know. It's a perfect example of a phenomenon that's been observed by researchers and non-researchers among different animals. For example, in our long-term field study of wild coyotes, we often remarked about how play was "socially contagious." And, having observed many thousands of play bouts in domestic dogs, other canids (members of the dog family), and other nonhumans, I've seen what could be called positive visual contagion on countless occasions, and many people have reported this phenomenon as well. In fact, there's an empirical study on dogs by Elisabetta Palagi, Velia Nicotra, and Giada Cordoni that demonstrates this phenomenon, but it was not called "positive visual contagion." (See "Rapid mimicry and emotional contagion in domestic dogs," "Dog Play Is Socially Contagious and Now We Know Why" for a summary of Dr. Palagi's study), Canine Confidential: Why Dogs Do What They Do, and "The Power of Play: Dogs Just Want to Have Fun.")

Among dogs and other animals, an action called the play bow is very important in initiating and maintain the "play mood," and in a summary of the above study by Jennifer Viegas (no longer available online) we read, "The researchers documented that in less than one second, many of the dogs would copy the expressions and behaviors of other dogs. For example, if one dog would position his body in a play bow, indicating readiness to play, another would do so near instantaneously. If a dog exhibited a relaxed, open-mouthed face—signifying friend not foe among canines—then the other dog would tend to do the same."

When I was asked to comment on the study by Dr. Palagi and her colleagues, I wrote that this is a very important study because not only does it extend the taxonomic distribution of rapid mimicry and emotional contagion to a species in which they have been inferred but not adequately demonstrated, but also because it explains a wealth of data showing that dogs (and other animals) can engage in high-intensity social play and "fine-tune it on the run." During decades of detailed research on dog play by my students and I, we hypothesized that dogs were somehow empathizing with their play partners and that this was one of the reasons that even high-intensity play only rarely escalated to "true aggression," but we hadn't invoked mimicry as one reason they could vigorously play and share intentions to play and maintain the play atmosphere. Now, Dr. Palagi and her colleagues have shown that the ability to maintain a "play mood" most likely rests on rapid mimicry and emotional contagion

One interesting aspect of Dr. Palagi's study is that "the distribution of rapid mimicry was strongly affected by the familiarity linking the subjects involved: the stronger the social bonding, the higher the level of rapid mimicry." Along these lines, a study in progress shows that play among dogs who are familiar does indeed differ from play among dogs who haven't previously played. We've also noticed that play in large groups of dogs breaks down more rapidly than play in smaller groups, not because it escalates into aggression but rather, we argue, that the dogs can't read one another as well in large groups. This remains an on-going study so please stay tuned for more information on this aspect of social play in dogs.

Where to from here?

"Overall, the findings of this study further highlight the importance of moving the analysis of animal social behaviour beyond the level of the interacting individuals, to take into account the broader social environment; in doing so, we feel there are a number of key avenues for future exploration."

Stay tuned for more discussion of the possible bases for sharing good feelings among group members without having to actually partake in a social interaction. There still is much to learn. For example, Berthier and Semple conclude, "Finally, it would be valuable to explore interspecific variation in this phenomenon to test, for example, whether propensity to positive contagion covaries with species’ social style (e.g. tolerant/despotic). Studies of these kinds are needed if we are to appreciate the role that positive visual contagion plays in the life of social animals." I totally agree. This surely is an exciting and very important field of inquiry for those people interested in social dynamics among group members and the factors that make individuals change their behavior when they observe others performing certain acts.


1"We predicted firstly that the observation of grooming would reduce bystanders’ rates of self-directed behaviour (prediction 1). We also predicted that observing grooming would reduce the time to bystanders' next grooming bout (prediction 2a), that levels of visual attention while observing grooming would be negatively related to the time to the next grooming bout (prediction 2b), and that observing grooming would increase the likelihood both of bystanders initiating grooming (prediction 2c) and of them being the groomer rather than groomee (prediction 2d). We predicted that observing grooming would increase bystanders’ rates of approaching other individuals (prediction 3a), the proportion of time they spent in close proximity to others (prediction 3b) and their rates of (non-grooming) affiliative behaviour (prediction 3c), but would reduce their rates of aggressive behaviour (prediction 4)."

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