Stress reduction through consolation in chimpanzees

Consolation behaviour is interesting in various ways. Why do some individuals spend effort going and doing consoling things to some others? Why, for that matter, don't they sometimes? Why does it sometimes help? When doesn't it?

One promising arena for shedding some light on these questions is observation of the smarter non-human social primates. (There are plenty of open avenues of enquiry here - one of my earlier posts on this blog relates to the effect of social support on perception of geographical slant, which is relevant to the "what does it do" question. I'd like to see some good neuroscience on some of this.) Chimpanzees sometimes enage in consoling behaviour, and it's possible to observe who consoles who, after what, and measure a host of other socially important considerations in detail that would be at least very difficult in humans.

Here's the abstract of the current paper:

Consolation, i.e., postconflict affiliative interaction directed from a third party to the recipient of aggression, is assumed to have a stress-alleviating function. This function, however, has never been demonstrated. This study shows that consolation in chimpanzees reduces behavioral measures of stress in recipients of aggression. Furthermore, consolation was more likely to occur in the absence of reconciliation, i.e., postconflict affiliative interaction between former opponents. Consolation therefore may act as an alternative to reconciliation when the latter does not occur. In the debate about empathy in great apes, evidence for the stress alleviating function of consolation in chimpanzees provides support for the argument that consolation could be critical behavior. Consistent with the argument that relationship quality affects their empathic responses, we found that consolation was more likely between individuals with more valuable relationships. Chimpanzees may thus respond to distressed valuable partners by consoling them, thereby reducing their stress levels, especially in the absence of reconciliation.

Note here that reconcilliation occurs between the conflicting parties, and is not what this study is about.

Here, roughly and leaving out a lot of detail, is what the authors did with a well-established group of chimpanzees varying in size from 26 to 32 members over the course of the study:

1. Observed aggressive conflict, defined as "any interaction involving a bite, hit, brusque rush, trample, chase, or threat in addition to screaming" (p8559). (Obviously a longer list would be needed for research subjects with access to firearms, lawyers, bagpipes and medium sized pieces of iron-mongery.) Conflicts were further analysed to determine who "won", since losing is taken to be more stressful.
2. Measured post-conflict (PC) stress by counting rates of self-grooming and self-scratching, both known to increase under stress. (As before, for subjects who can buy dumb stuff on E-Bay, bang tools together in their shed, etc., a richer coding scheme is required.)
3. Measured consolation behaviours, by counting affiliative interactions, defined as "kiss, embrace, grooming, finger-in-mouth, gentle touch, or play". (Exercise for the reader.)
4. Measured relationship quality between different pairs of chimps, using coding methods developed for use with mother-infant relatioships.

The details I've left out are important - this kind of primatology is tough, and depends on laborious examination and encoding of recordings of interaction and activity, before any analysis can begin. (It involves amounts of crushingly dull drudge work impossible before the invention of the scientific underclass known as the 'graduate student'.) The analysis here also depends on some specific policies dividing up time for coding purposes, and more specifically classifying episodes of consolation as a function of time since conflict.

Subject to the various coding schemes and data collection policies, the authors collected data on 234 pairs of episodes (ones involving post-conflict behaviour and matched controls lacking it) for 22 recipients of aggression, involving 129 distinct pairings of individuals in the original conflict. The sophisticated analysis (detailed in the paper and the supplementary materials) established the main finding: that consolation reduces stress, and that the best predictor of the effect of consolation was relationship quality: it's worth more to be comforted by those who matter to us. The two figures below summarise some of the main results.
























For another article on chimpanzees on this blog (not about consolation) see Chimpanzees use self-distraction to cope with impulsivity.

And for anyone who doesn't know, the picture at the top is Philippe from Achewood (used without permission) . He's got his own blog here.


Fraser, O.N., Stahl, D., Aureli, F. (2008). Stress reduction through consolation in chimpanzees. Proceedings of the National Academy of Sciences, 105(25), 8557-8562. DOI: 10.1073/pnas.0804141105