Third Party Punishment in Chimpanzees?

Today just after 6pm Swela, a relatively low-rank and highly-strung young adult female - and also my favourite female in the group, on account of her sad eyes and warm demeanour - started to scream. Riet, the giant and dominant female of the group, had stolen her blanket. Swela often carries a blanket, which she clutches to her chest as one would a child; but Riet also likes to sleep on the sack-cloth out of which they are made. When Swela screamed she ran towards other chimps and pushed her face close to theirs, baring her teeth, so as to present to them her distressed expression. Then she alternated her gaze back to Riet and then to her interlocutor. It was if she was saying "See what she's done to me! Look at my pain!".

(One advantage of posting these thoughts here is that when I'm being a proper scientist at work, I can't anthropomorphise the chimps to extent that I might here.)

One of the chimps whose attention was caught by Swela's screams was Kofi, a juvenile male. Kofi is beautiful, hilarious and, along with Swela, unquestionably my favourite of the A chimps. He has no fear and our keepers worry that he will grow up to terrorise the group, because despite being only 6, he spends his days throwing beetroots at the heads of the highest-ranking chimps - including Frodo, the alpha male and Kofi's best friend - and whipping them with sticks. (If he were a human child, we'd find it natural to describe his behaviour as 'testing the boundaries'. I don't know if that's really an appropriate way to describe Kofi's behaviour, because chimps may lack the understanding of behavioural norms that this would seem to imply.) When Kofi heard the screams, he looked at Swela, and followed her gaze to Riet, who was holding Swela's blanket. He then ran to Riet and started whipping her with the long stick he was holding.

Why is this interesting? Well, one possibility is that it's evidence of third party punishment in chimpanzees. Third party punishment lies at the origin of our legal system. Where someone violates a group norm in human societies, typically they are not themselves required to inflict justice on their aggressor. Rather, the state intervenes and does it for them. Third party punishment is foundational for human society because it centralises the balance of power, enabling the enforcement of norms where individuals might be powerless to act. It's therefore a very powerful mechanism for the enforcement of group norms, and the regulation of antisocial behaviour.

So was Kofi's behaviour an instance of third party punishment? Well, as with many cases of observation, it's very difficult to tell. A major worry here would be that Kofi is for the most part only too happy to whip his higher-ranking peers with sticks. In that case, this encounter could just be a coincidence, and point to nothing more profound than Kofi's violent tendencies. This reading of the scene would be reinforced by the fact that when my colleagues have run controlled studies designed to test for the presence of third party punishment in chimpanzee communities, they found no evidence (Riedl, Jensen, Call, & Tomasello: (submitted) No third-party punishment in chimpanzees). In other words: there was no significant difference in the tendency of chimps to punish between the test condition and the control conditions introduced to rule out alternative explanations.

It's not impossible that Riedl et al. failed to uncover a real phenomenon of chimpanzee behaviour. Nonetheless, given the combination of experimental findings and Kofi's whip-happy behaviour, it would surely be premature to conclude that he was engaging in third-party punishment - even if it is tempting.