Is great apes' monkey business the origin of human humour?

We've all had fun teasing our friends and family before. Such jokes will often be verbal - but scientists have also observed this behaviour in children as young as eight months old, which suggests that language is not an essential element of teasing: for example, a playful tap on the shoulder. In light of this, cognitive biologists have been seeking an origin for our sense of humour in our closest animal ancestors, and have observed teasing behaviours in all four great ape species, meaning it's likely to have been in our biology for at least 13 million years, as Erica Cartmill, from Indiana University, explains to Chris Smith...

Erica - I was studying gestural communication in orangutans, and I was watching this interaction between an infant orangutan and her mother. The infant orangutan was dangling over her mother. Mother was lying on her back in the straw, and the infant had a stick in her hand and she reached down the stick and sort of waved it over her mother. And as her mother reached up, her hand started to grab it, the infant pulled back the stick. That kind of, you know, here you go. Ha ha. Just kidding. Right? Give me five, too slow! And the infant kept doing it. She did it several times. The mother was playing along, didn't seem to get annoyed, kept sort of humouring the infant. I thought it was just absolutely charming. But what really fascinated me was when the infant stopped doing it, she dropped the stick. The mother then picked up the stick and started doing the same thing back to the infant. I really thought about it as having almost the structure of a joke. There's the setup, I'm offering you something and there's the punchline. I pull it back, right? There's the expected behaviour - take this thing and then the unexpected. Just kidding. And so that formed the centre of the kind of thing that I wanted to study in apes. I wanted to understand, was this something that they did a lot? Was this something that where they really, they understood what it meant for another to be surprised?

Chris - And obviously it fits in that group, in which we haven't shared an ancestor with some of the species you're mentioning for millions of years. This would argue that some of the behaviours we see in us, the reason we play with our children the way we do is exactly the same.

Erica - Absolutely. I wouldn't argue necessarily that the behaviours themselves are biologically inherited. You know, I'm not saying that we play peekaboo in the way that we do because of our biology, because of our genes, but I think we do things like play peekaboo because we do share underlying ideas about other individuals, what it means to interact with them. We understand that other individuals can have beliefs, they can have expectations, they can be surprised. You really need to, to understand something about their mind. And I think that those are shared across all of the great apes, those abilities.

Chris - How did you test that out though, to confirm for yourself that that was the case and that this is what's going on? This is a sort of primitive form of humour that has educational value.

Erica - Honestly, this is such a scientist's answer, but you know, it's something where more data needs to be collected. I mean, it's something that I think we're still exploring. I'm kind of going out on a bit of a limb here and saying, I think it's because of these kinds of understandings about other people, other individuals, that we see those behaviours. It's very hard to conclude that when you're just looking at behaviour. You can't interview an orangutan and say, what do you understand about this other individual? You need to draw on information from a wide range of sources. You need to look to see what they do spontaneously. You need to try to design clever experiments and games where we can see what they pay attention to? What information do they use? How do they make judgements in one situation versus another? In order to really fully answer that question. What we were doing in this study was kind of laying the groundwork for that. What we started with was one example, or you know, a handful of examples of what I had seen orangutans do. And I wanted to build a corpus of behaviours. I wanted to build a data set. Do they all look like this? I offer something and I pull it back at the last second. Or are there other kinds of behaviours that might have similar underlying structures, but appear quite different on the surface?

Chris - Do you think this goes beyond just higher animals like these primates that you are describing though? Because my dog turns up with a toy and will torment me because they'll wave it in front of me and then whip it away before I have the chance to take it off him. And it's clearly a game. They clearly are getting something out of it. Why would other animals be doing that?

Erica - I think that's one of the things that we hope will come out of this study. This isn't the first time anyone has seen these behaviours. You go to a zoo and you watch apes, you'll see some of them and you know, it'll probably be familiar to pet owners or people that work with or watch other animals. The thing that really we were trying to do is to argue that there isn't a sharp division between aggression and play. That there's an interesting grey area in between where what you do can be interpreted as playful or it can be interpreted as mean. And I think learning to navigate that space, learning what's appropriate with which individual, is something that social animals in particular have to figure out in order to thrive in their groups. And this is something that we know humans do. Now we know great apes do it. And so our hope is really that by sort of shining a light on this kind of behaviour and defining it and describing it as its own thing, we will encourage other people to look at it in a different way and to really start paying attention to it. And we'll start to collect examples, similarities, and differences across a wide range of species.