The Origins of Disgust

published on July 9, 2020

Being impressed by the cognitiveabilities of a chimpanzeeisn't just good for them,it is good for us,because it helps us learn aboutour own evolutionary historyComparing the psychologyof humans to the psychologyof other primatesis a great way toilluminate what it is wemaintained, lost, or changedas our brains divergedfrom other primatesNow, I'm really excitedright now, because inthe spirit of sharing,

The Primate Research Institutehas agreed to show mesome of the other waysthey're learning about usby studying thosewho are almost us I'm heading to the parasite lab to meet up with associate professor Andrew McIntosh and doctoral student Cecile Serabian

Their work with Japanese macaques has led them to theorize that primates' feelings of repulsion or disgust could have served a protective purpose in our evolution To study disgust, we will be working with one the most famous disgust inducers: poopAndrew, Cecile, thank youfor meeting up with me,

I can now tell people thatmy time in Japan was crappy Just likeevery day for usSo tell me, why is therea bunch of poop on the table?Because we were studyingthe social behaviorand parasite infectionof the macaquesRight

If we want to say that humansare somehow especially hygienicor disgusted by those kinds ofobjects that might make us sickIt's quite difficultto separate whether that'san evolutionaryresponse to somethingor just a culturalphenomenon that we'vekind of created on our ownNow these are clearly toys

They're made of plasticThese lookkind of differentOkay, so you have differenttypes here on the tableThis is the typefor carnivores–it's not the type of primatesPrimates have a long-shapetype of poop

It's called type 9-So those are all—Wait, poops have numbers?–I only know number 2Why make play poop when youhave plenty of chimps out theregiving you real poop to use?Ah-So there's no odoror texture here-Yeah, exactly

And what differencesdid you see?Ah, so it's like a surfaceto put the food on top of-They would avoid the replica?-YesOh, really? Right, rightIf you expose a bunchof individuals to a rangeof different kinds ofavoidance experimentswe found that

Those individuals thatare much more hygienicactually were exhibitinglower infection, soIt sounds like a reallystrong argument in supportof the idea that weevolved an emotion like disgust- or a behavior like avoidanceof infectious-looking stuff- Mm-hmm-Because it had an advantage

-You get infected less- That's rightSo you have some kindof experiment for me?-Yep-Is it safe?-Let's see-Don't play that way!- Cecile and Andrew wanted to show me just how hard-wired our sense of disgust is There you go

Okay Those are edible?-Yes, those are edible-Mm-hmm-I'm just going to place onein each of the holes here-OkayIf you are ready to eat them,just try to reach out for themOkayOkay Good Good

What do I do onceI pull the treat out?You will tell uswhether you are ready toeat it or not, basicallyOh, okay-So, you'll put one in there-One goes hereSure-One goes here-Okay

And one goes thereAll right, I'm going tostart right in the middleHmm All right, so I might justblow on this before I eat it,but I feel prettyready to eat it-Yeah?-Because what I felt was dry,and it was solid,it was like a foam

Watch-Okay-Oh, it's really goodIt's got kind of a coffee tasteSo far so goodI'm going to go to the leftNo, I don't want this one-Okay-Whoa, you still went for it

I still pulled it outWhat was it?So I'm just goingto set it down OkayAlright, it smellsit's kind of fishyAll right, nowI okay

I'll tell you what,that was disgusting interms of how it felt,but when I see the color, I seethis kind of bright green colorthat makes me feel lessdisgusted actuallybecause it's sort of a funcolor and it reminds methat it probablyisn't truly contaminatedBut this is the one thatI'm least likely to want to eat

Even stronger than the visualcues or the olfactory cuesit seemed that that touchingsome substrate like thisgave us the strongestaversive responseYeahSo the first one you touched-was this piece of foam here-Yeah

-So yeah, it's basically dry-SolidUm, then I think youwent here, and thatis called konnyakuYeah, konnyaku is a kind ofstarch-based gelatinwhich is part ofthe cuisine hereYou said it smelled fishy,so in here you probablyhave parts of seaweedYeah, right, that's wherethat's coming from

It's soft, a bit wet,but not very-It's not sticking to me-Not sticky, yeahAnd the last one here waswhat maybe kids in the '90sincluding myselfwere playing withA slime toyWhich is likeslimy and sticky

And this,it's just so gooeyWell, and the fact that it'spink makes it so much more funthan if it was like, brownMm-hmmNow, the research you'redoing with macaques,is that somethingI could observe?

We'd be willing to take youout to the macaque habitatand we could run some of thesesimilar experiments with them-for you to observe-Ooh I would love to Yeah Cecile's work with macaque monkeys on Koujima Island led her to develop an experiment that she and Andrew have been runningon the macaques here atthe Primate Research Institute

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- And here they are- And here they areOh look at that,the babies are so cute-Here it's feeding time, almost-Mm-hm

Which is a good timefor an experimentYeah, we're a bit lucky,they didn't eat thatmuch in the morning,so hopefully they'll have thatextra motivation to participateAnd we're going to tryto play a bit withthe value of the food,-so we'll start with theirregular monkey chow-RightWhich they see a couple timesa day on a daily basis

And then we'll see whathappens when we introducethat nice, tasty peanut Right And so, I'massuming they like peanuts-Right, so—They don't like peanutsin or on poopWell hopefully, we'llfind that out today Okay,so it looks likeAndrew is dumping the, um

Those are real fecesthat he is going to pairwith the replica fecesthat we have seen in the lab,and a control brown wood chip- Near each other?- Yes, near each otherAha, all right-Let the games begin-Yeah

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 They're lookingnow here comes one- No oh, oh!- YeahNo, he's smelling the wood chip

He smelled the wood chip,the monkey chow fell off of it YesIs he gonna eat it?No I thinkregular old normal foodon poop is just–it's a hard sellShelled peanuts, okay

– So that'son the fake poop- Yep-That's on the real poop- Yeah-And that's on the wood block- Yes This time around, Andrew introduces peanuts, which the macaques really loveWill this special treatoverride their inner instincts?Oh, oh, they'realready running in

Ooh But he threw it-And he's washing it now-He's washing itAll right, herecomes another oneOh, he went for the poop one!- Yeah-

The first one,he just wants it to roll-He doesn't even wantto have to carry it- In the waterThis is rolling, so, theydo some of those behaviorsAnd now he's washingit in the water,- Yeah- Is it clean enough?Oh, still gotta roll

That was incredible,because the peanuts thatwere just on the wood chip,those went straightinto monkey mouths Was this an aberration? Andrew reloaded the peanut baits to find out- Decoy- A female isapproaching Yep, here she is

She smells it first,and then– and then— Smells it again- Believes it, eats it- On the fake- That wason the fake, yeahVery coolNow she already ate offthe decoy and it was safeShe hasn't, oh she putthe control right in her mouth

– Yes- And she's goingto wash the real feces YeahAnd she went forthe real feces lastYes, she did She's gota baby with her,so I really hopeshe cleans that

Or maybe that'sthe disadvantage,she's carrying a baby,she cannot afford, like,cleaning everythingYeahI'm reallyamused by how theyvisually recognize feces-I mean we're far away,it's hard for me to tell,-Yesbut they can see that shapeor texture–

-"Be wary"-Yeah Over the course of several rounds of the experiment, the monkeys would eat off of the control, wash food from the replica, and be extremely hesitant towards anything that touched poop The macaques demonstrated a clear and strong sense of disgust

That was driving their decisionmaking and potentially keepingthem safe from pathogens With the experiment complete, Dr McIntosh returned topside so we could discuss our findingsSo did you enjoythe view from up here?They did exactly what wetalked about earlierReady to avoid, parasiteinfested potential things

Yeah, I mean it'spretty clear, there's nota complete hesitationto pick up thingson actual fecesbut the reactions thatthe monkeys give when they do sois just so clearly differentthan when they are pickingthings off the groundor off the control itemsthat they have hereYeah, yeah, in fact,I, you know, I only sawa few trials here,

But as soon as the peanutor the monkey chow onthe feces is picked upand they realize thatthe feces is coming with itit's a sticky substanceand that was when theirrevulsion got largerIt almost seemed like theymight be absent-mindedly going"I don't care,"-and something deeper in themwas like, "you should care, youshould throw this,"- Yeahroll it, wash it,so it makes sense froman evolutionary standpoint

Well, Cecile, Andrew,thank you again so much forletting me come out hereto see a primateexperiment in actionThis was really phenomenalThank you- You're welcome-Thanks for coming

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