The Origins of Disgust

[00:08] Being impressed by the cognitive abilities of a chimpanzee because it helps us learn about our own evolutionary history. Comparing the psychology of humans to the psychology of other primates

[00:23] is a great way to illuminate what it is we maintained, lost, or changed Now, I'm really excited right now, because in the spirit of sharing,

[00:35] some of the other ways they're learning about us by studying those who are almost us. with associate professor Andrew McIntosh

[00:49] Their work with Japanese macaques has led them to theorize could have served a protective purpose in our evolution.

[01:01] one the most famous disgust inducers: poop. I can now tell people that my time in Japan was crappy.

[01:18] So tell me, why is there a bunch of poop on the table? and parasite infection of the macaques. [Cecile continues]

[01:34] Right. If we want to say that humans are somehow especially hygienic

[01:47] or disgusted by those kinds of objects that might make us sick an evolutionary response to something [Michael] Now these are clearly toys.

[02:04] Okay, so you have different types here on the table. it's not the type of primates. It's called type 9.

[02:19] -[both chuckle] -I only know number 2. Why make play poop when you have plenty of chimps out there giving you real poop to use?

[02:34] Ah. And what differences did you see?

[02:46] [Cecile continues] Ah, so it's like a surface to put the food on top of.

[03:07] [Cecile continues] If you expose a bunch of individuals to a range of different kinds of

[03:21] those individuals that are much more hygienic It sounds like a really strong argument in support of the idea that we - or a behavior like avoidance of infectious-looking stuff. - Mm-hmm.

[03:38] -You get infected less. -[Andrew] That's right. -Yep. -Is it safe? Cecile and Andrew wanted to show me just how hard-wired our sense of disgust is.

[03:54] [Cecile] There you go. -I'm just going to place one in each of the holes here. -Okay.

[04:07] Okay. What do I do once I pull the treat out?

[04:22] Oh, okay. -One goes here... -Okay. All right, I'm going to start right in the middle.

[04:40] Hmm. All right, so I might just blow on this before I eat it, -Yeah? -Because what I felt was dry, and it was solid, it was like a foam.

[04:53] -Okay. -Oh, it's really good. It's got kind of a coffee taste. I'm going to go to the left. -Okay. -Whoa, you still went for it.

[05:09] [sniffing] So I'm just going to set it down. Okay. Alright, it smells... it's kind of fishy.

[05:22] [chuckles knowingly] I'll tell you what, that was disgusting in terms of how it felt,

[05:35] but when I see the color, I see this kind of bright green color because it's sort of a fun color and it reminds me But this is the one that I'm least likely to want to eat.

[05:50] Even stronger than the visual cues or the olfactory cues it seemed that that touching some substrate like this So the first one you touched

[06:03] -So yeah, it's basically dry. -Solid. Um, then I think you went here, and that is called konnyaku. which is part of the cuisine here.

[06:18] Yeah, right, that's where that's coming from. -It's not sticking to me. -Not sticky, yeah. And the last one here was what maybe kids in the '90s

[06:33] Which is like slimy and sticky. Well, and the fact that it's pink makes it so much more fun

[06:45] Now, the research you're doing with macaques, We'd be willing to take you out to the macaque habitat -for you to observe. -Ooh. I would love to. Yeah.

[07:02] led her to develop an experiment that she and Andrew have been running They want to know if macaques avoid feces

[07:15] because a feeling of disgust evolved in order to reduce the risk of their exposure to parasites. Oh look at that, the babies are so cute.

[07:30] Which is a good time for an experiment. so hopefully they'll have that extra motivation to participate. -so we'll start with their regular monkey chow. -Right.

[07:45] And then we'll see what happens when we introduce that nice, tasty peanut. [Michael] Right. And so, I'm assuming they like peanuts.

[07:57] -Right, so-- -They don't like peanuts in or on poop. Well hopefully, we'll find that out today.

[08:09] Andrew is dumping the, um... that he is going to pair with the replica feces that we have seen in the lab, and a control brown wood chip.

[08:22] Aha, all right. For the first trial, Andrew places monkey chow on the control block of wood, the replica feces and the real feces.

[08:37] Whether or not the macaques eat it may indicate their level of disgust. [Michael] They're looking... now here comes one. [Michael] He smelled the wood chip, the monkey chow fell off of it.

[08:51] [Michael] Is he... gonna eat it? No. I think regular old normal food on poop is just-- [Andrew over radio]

[09:07] -[Cecile] So that's on the fake poop. -[Michael] Yep. -[Michael] And that's on the wood block. -[Cecile] Yes. This time around, Andrew introduces peanuts, which the macaques really love.

[09:23] Oh, oh, they're already running in. [Michael] But he threw it.

[09:36] All right, here comes another one. -[Cecile] Yeah. -[Michael laughs] -He doesn't even want to have to carry it. -[Cecile] In the water.

[09:48] This is rolling, so, they do some of those behaviors. Oh, still gotta roll. those went straight into monkey mouths.

[10:03] Andrew reloaded the peanut baits to find out. [Michael] Yep, here she is. -[Cecile] Smells it again. -[Michael] Believes it, eats it.

[10:16] Very cool. She hasn't, oh she put the control right in her mouth. [Cecile] Yeah.

[10:31] Yes, she did. so I really hope she cleans that. she's carrying a baby, she cannot afford, like, cleaning everything.

[10:45] I'm really amused by how they visually recognize feces. but they can see that shape or texture--

[11:00] Over the course of several rounds of the experiment, wash food from the replica, and be extremely hesitant The macaques demonstrated a clear and strong sense of disgust

[11:17] that was driving their decision making and potentially keeping them safe from pathogens. With the experiment complete, Dr. McIntosh returned topside So did you enjoy the view from up here?

[11:32] Ready to avoid, parasite infested potential things. Yeah, I mean it's pretty clear, there's not a complete hesitation but the reactions that the monkeys give when they do so

[11:49] is just so clearly different than when they are picking things off the ground Yeah, yeah, in fact, I, you know, I only saw a few trials here, but as soon as the peanut or the monkey chow on the feces is picked up

[12:05] it's a sticky substance and that was when their revulsion got larger. It almost seemed like they might be absent-mindedly going "I don't care,"

[12:17] roll it, wash it, so it makes sense from an evolutionary standpoint. to see a primate experiment in action.

[12:32] -[both] You're welcome. -Thanks for coming.