--- title: 'The Origins of Disgust' source: 'https://youtube.com/watch?v=PJF-cbTC4Cg' video_id: 'PJF-cbTC4Cg' date: 2026-07-19 duration_sec: 764 channel: 'Vsauce' --- # The Origins of Disgust > Source: [The Origins of Disgust](https://youtube.com/watch?v=PJF-cbTC4Cg) ## Summary This video explores the evolutionary origins of disgust by comparing human behavior with that of Japanese macaques. Researchers Cecile and Andrew McIntosh conduct experiments to determine whether macaques avoid feces due to an evolved disgust response that reduces parasite exposure. ### Key Points - **Comparative Psychology** [00:08] — Comparing human psychology to other primates helps illuminate what traits we maintained, lost, or changed during evolution. - **Disgust and Hygiene** [01:01] — Research with Japanese macaques suggests that disgust may have evolved as a protective mechanism against parasites and infection. - **Human Disgust Experiment** [03:54] — Michael participates in a blind taste test with foods of varying textures and smells, demonstrating that tactile cues (slimy/sticky) trigger strong disgust. - **Macaque Experiment Setup** [07:02] — Researchers present macaques with monkey chow and peanuts placed on control wood, replica feces, and real feces to test disgust-driven food avoidance. - **Macaque Behavior** [10:31] — Macaques visually recognize feces and often wash or roll food that contacts it, showing clear disgust and pathogen avoidance. - **Evolutionary Significance** [11:17] — The macaques' strong disgust response supports the idea that disgust evolved to reduce infection risk, similar to humans. ### Conclusion The experiment demonstrates that disgust is an evolved response to avoid pathogens, shared across primates. This research highlights the deep evolutionary roots of hygiene behavior. ## Transcript 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 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, some of the other ways they're learning about us by studying those who are almost us. with associate professor Andrew McIntosh Their work with Japanese macaques has led them to theorize could have served a protective purpose in our evolution. one the most famous disgust inducers: poop. I can now tell people that my time in Japan was crappy. So tell me, why is there a bunch of poop on the table? and parasite infection of the macaques. [Cecile continues] Right. If we want to say that humans are somehow especially hygienic or disgusted by those kinds of objects that might make us sick an evolutionary response to something [Michael] Now these are clearly toys. Okay, so you have different types here on the table. it's not the type of primates. It's called type 9. -[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? Ah. And what differences did you see? [Cecile continues] Ah, so it's like a surface to put the food on top of. [Cecile continues] If you expose a bunch of individuals to a range of different kinds of 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. -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. [Cecile] There you go. -I'm just going to place one in each of the holes here. -Okay. Okay. What do I do once I pull the treat out? Oh, okay. -One goes here... -Okay. All right, I'm going to start right in the middle. 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. -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. [sniffing] So I'm just going to set it down. Okay. Alright, it smells... it's kind of fishy. [chuckles knowingly] I'll tell you what, that was disgusting in terms of how it felt, 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. 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 -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. 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 Which is like slimy and sticky. Well, and the fact that it's pink makes it so much more fun 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. led her to develop an experiment that she and Andrew have been running They want to know if macaques avoid feces 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. 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. And then we'll see what happens when we introduce that nice, tasty peanut. [Michael] Right. And so, I'm assuming they like peanuts. -Right, so-- -They don't like peanuts in or on poop. Well hopefully, we'll find that out today. 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. Aha, all right. For the first trial, Andrew places monkey chow on the control block of wood, the replica feces and the real feces. 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. [Michael] Is he... gonna eat it? No. I think regular old normal food on poop is just-- [Andrew over radio] -[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. Oh, oh, they're already running in. [Michael] But he threw it. All right, here comes another one. -[Cecile] Yeah. -[Michael laughs] -He doesn't even want to have to carry it. -[Cecile] In the water. This is rolling, so, they do some of those behaviors. Oh, still gotta roll. those went straight into monkey mouths. Andrew reloaded the peanut baits to find out. [Michael] Yep, here she is. -[Cecile] Smells it again. -[Michael] Believes it, eats it. Very cool. She hasn't, oh she put the control right in her mouth. [Cecile] Yeah. Yes, she did. so I really hope she cleans that. she's carrying a baby, she cannot afford, like, cleaning everything. I'm really amused by how they visually recognize feces. but they can see that shape or texture-- 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 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? 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 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 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," roll it, wash it, so it makes sense from an evolutionary standpoint. to see a primate experiment in action. -[both] You're welcome. -Thanks for coming.