Following up from my appearance on Planet Watch Radio, LM asked
“What is bonobo’s capacity for humor and what function does that serve?”
A brief (and admittedly unsatisfying) answer on humor in bonobos and other great apes is that it is related to play. All of the great apes spend a lot of time in social play as juveniles, and when they do, they exhibit what is called a ‘play-face’ that seems to be analogous to laughter . The ‘play-face’ is an indication that behavior has benign intentions – slapping and wrestling are ‘for fun’ and practice, rather than aggressive. Even as adults, all great apes ‘laugh’ when physically tickled, and all adult great apes spend some time playing also (just not as often as juveniles). The non-human apes don’t have as much diaphragm and vocal control as we do, so their laughter is mostly facial and ‘breathy’ rather than being vocalized the way humans do.
Probably (just as is probably true in most human cultures) the main function of humor is to reduce social tension and improve social bonds within a group. As you can imagine, humor is difficult enough to study and comprehend across human cultures, so it is very hard to investigate in other species. However, since bonobos and chimpanzees are such close cousins to us, it is not unreasonable to interpret the combination of facial expressions and contexts as probable humor. In relaxed and fairly congenial captive settings like there were at the Language Research Center, we often found that the bonobos in particular liked to ‘prank’ the humans around them (most especially, holding water in their mouth for several minutes so they could spit it on an unsuspecting passer-by). They also would grab items like hats or shoes from people, then wear them. And the language skills they learned allowed them to express a little word play and apparent sarcasm. My take on their facial expressions was that they found this hilarious!
There are also many stories about Koko that appear to be her playing jokes on those around her. I suspect that humor is something that is common to very social, very intelligent species (and I’m not alone), and I would not be at all surprised if those who spend lots of time with elephants or dolphins find indications of humor in them, also. It doesn’t get into the scientific literature much, because it’s very difficult to provide convincing evidence – so much relies on interpretation, and that kind of subjectiveness does not hold up in the peer-review process.
 Cordoni, G., & Palagi, E. (2012). Primate Play Laughing: a Comparison Between Immature Great Apes and Humans. Journal of Biological Research, 85(1), 297.