Even before they learn to talk, human infants and toddlers know how to joke: They play games such as peek-a-boo and take whatever unexpected actions get a rise from adults. Now, it appears that nonhuman apes—like gorillas and orangutans—engage in similar behaviors, according to a paper published last week in Biology Letters.
Science chatted with co-author Erica Cartmill, an anthropologist at the University of California, Los Angeles, about what these “playful teasing” behaviors look like in our evolutionary cousins.
This interview has been edited for clarity and length.
Q: How did you get interested in this topic?
A: I was studying how orangutans communicated with one another [in captivity], and I noticed several interactions where one orangutan would have an object, and they would extend it out toward the other one. As the other one went to reach for it, they would pull it back. But rather than get annoyed, the other one would just drop their hand, and then they both would do it again. It seemed to be something that was mutually enjoyable. In a couple of cases, they would even swap roles: The orangutan that was doing this teasing behavior would get bored and drop the object, and then the other one would pick it up and start doing it. The behavior seemed very gamelike, with specific rules and structure, and resembled the kind of thing that toddlers do.
Q: Are there other types of teasing behaviors?
A: One is called “provocative noncompliance,” where I’m doing something that goes against what you want me to do, and I’m doing it in a way that is meant to provoke you. In human infants, for example, the mom tells the child to put on shoes, and the child takes a shoe, looks at the mom, and then puts the shoe on the top of their head. This type of behavior was observed in apes raised with humans explicitly trained to communicate with sign language or a keyboard-based system.
Q: Like Koko, the gorilla taught sign language?
A: In one instance, when the caregivers were interacting with Koko, they asked her “What do [we] use to clean your teeth?” Koko signed “foot.” And then they asked her “What do [we] put on your toothbrush?” Koko then signed “nose.” A completely bizarre response, but then she lifted her foot up to her nose. It’s not just that she’s produced the wrong signs, but she produced the wrong signs and then acted out this weird interaction. This relies on an understanding of the communicative symbols and the ways in which they’re supposed to be used, and then using them in unexpected ways.
A third type of teasing is disruptive behavior—not just being generally disruptive, but disrupting someone else’s activity in a way that has an element of surprise. In apes, the mother could be sitting, cracking a nut open with a stone, and an infant does a somersault in the place where she is working.
Q: How do you know that an animal is being playful, rather than trying to irritate or provoke another individual?
A: Teasing should really be considered as a behavior that exists on a spectrum. Sometimes it is negative and can lead to aggression or bullying, and sometimes it’s positive and can lead to social bonding, just as a joke told by a human can be interpreted a playful quip between friends or something that’s very offensive.
For a teasing event to be playful rather than aggressive, both individuals have to perceive it as playful. One of the things we don’t know yet—and what I’m hoping to show in this project I’m working on now—is whether there are any behaviors of the teaser that predict whether the teasing leads to the target running away or responding aggressively versus a play session. I think we need to try to understand the relationship between the physical interaction and all of the social inferences that are being made.
Q: What does it mean that apes have these behaviors, which are similar to toddlers?
A: I don’t want to say that just because you see something in toddlers, you should expect it to see in apes. That being said, I think it can tell us a lot about the potential building blocks of human social cognition, in particular the kinds of inferences that humans make when they’re developing friendships, enemies, or frenemies. So much of the work on human social relationships relies on language, particularly when we are talking about things like humor.
People have thought for a long time that humor—in particular, joking—relied on a fairly sophisticated understanding of language. I’m not saying that playful teasing is the same thing as humor, but it is getting there. Particularly in provocative noncompliance or offer/withdrawal behaviors, there is a moment of incongruence. Something that that is unexpected, something that’s out of context, or something that that sneaks up on you are all things at the heart of humor.
Q: What are you working on now?
A: Nonhuman apes, just like human apes, can contract COVID-19, so there has been a huge pause put on research that involves interacting with great apes in any way around the world. So, we’ve switched to doing a video study identifying and characterizing teasing behavior. I’m also collaborating with some scholars at the Max Planck Institute, the University of Edinburgh, Johns Hopkins [University], and Harvard [University] to do a study using eye tracking with apes. This past weekend, I filmed some stimuli for a video that we’re going to use in the study, which involved me dressing up in a gorilla suit and jumping around with my husband. So that’s been a fun project to set up, and hopefully in 2021 we will be able to run that study.
Q: In the meantime, you can continue to teach people about teasing in apes.
A: I hope that in these fairly stressful times, thinking about apes playfully teasing each other and possibly having an appreciation for humor provides some levity and diversion. But hopefully in a way that raises some serious questions and implications about our own evolutionary history.