Your shit dont stink

September 24, 2012 5:22 PM

Humans generally dislike the smell of feces. Is that dislike innate, or culturally acquired?

Related: do any humans find the smell of feces appealing or simply neutral? Such as scat fetishists, for instance?

posted by dontjumplarry to science & nature (25 answers total)

If poop smelled good, people wouldn't avoid it. Shit is germy, so one should stay away. Nature would select for people who didn't like poop-smell.
posted by etc. at 5:26 PM on September 24, 2012 [4 favorites]

I say it's acquired. Babies don't think their feces is gross; they have to be taught. If you didn't train children to be disgusted by feces, they would- and do! happily play in it.

Also, jasmine, widely acknowledged as being an alluring and sensual fragrance, and an important note of many different perfumes, is said to have a hint of fecal aroma in its makeup. So there's that.
posted by windykites at 5:34 PM on September 24, 2012 [1 favorite]

I was watching some poop-eating dogs last month and wondering the same thing. The "it's germy so we should stay away" evolutionary argument doesn't seem to keep them away from it.
posted by feets at 5:35 PM on September 24, 2012 [1 favorite]

Baby boop doesn't really get smelly until they're 2-3 years old, unless the baby eats formula.
posted by Chaussette and the Pussy Cats at 5:36 PM on September 24, 2012 [1 favorite]

Acquired.

I think poop and some chocolates smell similar, though chocolate is good and poop smells bad once you know which is which.

Much like the Parmesan cheese / vomit duality.
posted by bottlebrushtree at 5:45 PM on September 24, 2012 [3 favorites]

Related: I don't like the smell of human feces. But a horse or cow barn? It's fine.
posted by windykites at 5:45 PM on September 24, 2012 [8 favorites]

Val Curtis, at the London School of Hygiene & Tropical Medicine, believes that disgust is genetic.
posted by bassomatic at 5:52 PM on September 24, 2012 [1 favorite]

Keep in mind that modern sanitation subjects us to poop only in very limited circumstances. The stuff used to be everywhere, and smelling it in public was a common thing, at least in urban settings.
posted by werkzeuger at 5:55 PM on September 24, 2012 [2 favorites]

Disgust may be genetic, but that doesn't mean smell preferences are.

If they have had no prior exposure, infants and young children do not differentiate between odors that adults typically find either very unpleasant or pleasant. For example, studies by Trygg Engen and colleagues showed that newborns gave the same response to asofedida (foul onion) and anise (licorice). Similarly four-year olds did not show different emotional reactions to butyric acid (rancid cheese) and amyl acetate (banana). The typical response to all these odors was avoidance. Other research with infants has even shown that sometimes they demonstrate responses opposite to those of adults, for example, liking the smell of synthetic sweat and feces. But by age eight, most children’s responses to odors mimic those of adults in their culture.

From an article discovered in the ever-intriguing Edible Geography.
posted by reren at 5:56 PM on September 24, 2012 [8 favorites]

I think many humans find the smell of other peoples' poop disgusting. But their own? I'm not so sure.
posted by yaymukund at 6:21 PM on September 24, 2012 [1 favorite]

I vote for a strong biological component. The molecules responsible for many bad smells—feces, rotten eggs, halitosis, trash, decaying matter, etc—are sulfur compounds like hydrogen sulfide and methanethiol. These compounds are produced as a byproduct of bacterial metabolism, and the human nose is unusually adept at detecting them; the "odor thresholds" for sulfur compounds are orders of magnitude smaller than for many other common substances. And they tend to be almost universally described as unpleasant. The tempting conclusion (and I think the most likely one) is that humans evolved a sensitivity for and aversion to sulfur compounds as a means of avoiding bacteria-induced illness. Not just so that we would avoid substances like feces, but so that we would avoid eating rotting plants and animals as well.
posted by dephlogisticated at 6:37 PM on September 24, 2012 [4 favorites]

19th C. ethnology deserves all kinds of caveats, but here's some ... food for thought: John G. Bourke (1891), Scatalogic Rites of All Nations. Incidentally, the author and Frank Cushing somewhat famously attended a ritual of a Zuñi secret society that involved urine-drinking and (possibly) coprophagia.

I haven't read my own source, but I'll add that in all my years of reading ethnography, I've never heard of any group using poop for perfume and meaning that the smell alone is pleasant. I guess it could happen, but I'd only expect to see it used for stuff like fuel, housing, insulation, and mosquito repellent or for symbolizing boundary disruption, which I'd guess is what the majority of Bourke's book is about.

My money says there's usually some sort of biological propensity involved in not liking it and an element of practicality in using it, but that it's still a pretty flexible, biologically undetermined issue.
posted by Monsieur Caution at 6:46 PM on September 24, 2012

I think dephlogisticated has got it, but I think it's also acquired to a certain extent.

Also: I was watching some poop-eating dogs last month and wondering the same thing. The "it's germy so we should stay away" evolutionary argument doesn't seem to keep them away from it.

Dogs have a digestive system designed to handle massive loads of bacteria that would be harmful to humans (carrion, for example) and so this comparison doesn't work.
posted by Specklet at 7:04 PM on September 24, 2012 [1 favorite]

The uniqueness of poop odour is largely through the presence of substantial amounts of indole, a product product of the bacterial breakdown of tryptophan. As Wiki will tell you, in trace amounts, it has a flowery note. I suspect that disgust as a reaction is innate, but disgust for poop specifically is learned, and is largely based on the scent of indole as the key fragrance note.

There's a lot of associations about waste products and smell and genitalia and clean v. dirty that get all mingled up when we're babies. There are cultural traditions which get overlaid with parental preferences which get factored into our own reactions. So I doubt there's an easy answer other than: "it Depends."
posted by seanmpuckett at 7:24 PM on September 24, 2012 [1 favorite]

Well, I can't stand the smell of jasmine or human poop. There's a handful of different things I've encountered that at least sort of touch off my "ugh, poopy smells" revulsion reflex - for instance, bleach that's been in contact with pretty much anything at all (other than the inside of a bleach bottle, I guess) reminds me very, very strongly of poop smells even though it doesn't smell like (most) poop - certainly it doesn't smell like any baby/toddler poop I've ever smelled, or like any port-a-potty I've been inside. I figure I must have just lived with enough people with bacterial issues that I somehow got the two scents connected in my brain.

Which is why I'm leaning towards "it's a cultural thing." But, it's definitely advantageous from a health standpoint, so I'm not shocked most humans in developed countries (where we all communicate back and forth with one another) share the same preference.

I meanwhile, like windykites, find horse/cow manure only mildly off-putting at worst.
posted by SMPA at 7:27 PM on September 24, 2012

Don't think animal scat's relevant to this discussion; it's different with the beasts. A lot of what they eat passes right through some of the biggest critters -- I read how elephant dung's only about 45% 'processed' and since they eat entire branches off of trees, one can dig around in their droppings and find whole, intact fruits. Human systems are way more efficient (but to me, dog shit smells even worse than human).

My vote's for innate.
posted by Rash at 8:10 PM on September 24, 2012

FYI breastfed babies' poop doesn't smell bad at all. Comparatively at least.
posted by bq at 8:12 PM on September 24, 2012

Rash: Human systems are way more efficient (but to me, dog shit smells even worse than human).

FWIW, you're probably basing that off of dogs who eat commercial dog food.

My dog is on a raw diet; his feces are (relatively) tiny, and very, very quickly decompose. (They're typically white by the next day or so.)

And at the dog park, I can tell if I've found his droppings or not (large area, and he never ever poops near people, so I have to search) by the smell. His smell faintly of rotten meat. Other dogs' poop can be smelled before I even bend to pick it up.

Anyway, long story short: poop is smelly.
posted by IAmBroom at 8:47 AM on September 25, 2012

Specklet:
Dogs have a digestive system designed to handle massive loads of bacteria that would be harmful to humans (carrion, for example) and so this comparison doesn't work.

In fact, this is a specific survival trait for (wild) mothers of newborn pups. They have to keep the burrows clean, but the pups are too young to venture out (and lack timing control anyway), so the mother will clean up all dinner byproducts orally.
posted by IAmBroom at 8:54 AM on September 25, 2012

so the mother will clean up all dinner byproducts orally.

...as does my beagle :- |
posted by Doohickie at 11:16 AM on September 25, 2012

My dog is on a raw diet; his feces are (relatively) tiny, and very, very quickly decompose. (They're typically white by the next day or so.) [...] Other dogs' poop can be smelled before I even bend to pick it up.

Same with my dog.

Sometimes when we're out for a nighttime walk I wonder how hilarious it must seem to him that I wave my phone around as a faint flashlight to find the feces in the dark. "Um, they're right there in front of your nose!" Dude...in case you hadn't noticed, my so-called nose isn't good for much.
posted by tangerine at 12:56 PM on September 25, 2012 [1 favorite]

Inate.
We are born liking sweet tastes...in nature, sweet typically means ready-to-eat and high caloric content. Just the opposite ...a foul smell typically means rotten, trouble, sick-making stuff.
posted by artdrectr at 3:15 PM on September 25, 2012

I frown upon it
posted by jb2824 at 5:55 PM on September 25, 2012 [1 favorite]

Inate. Absolutely.
posted by victory_laser at 1:55 AM on September 26, 2012

Aroma Scientist checking in!

The general consensus about aversion, from the literature I've read, is that specific TASTE aversions (e.g. aversion to bitterness) are innate and probably evolutionarily-based, but that specific SMELL aversions are learned. For example, young babies will be averse to specific tastes, such as bitterness, but not generally to specific aromas. Especially intense aromas might be distressing to babies, regardless of their particular smell, because of their intensity. However, there is evidence that olfactory receptors begin functioning in a fetus at about 3 months gestational age, so, even newborns have had about 6 months of exposure to aromas (e.g. through what their mother has been eating) and correspondingly 6 months to begin liking those particular aromas by the time they are born. And, for human, liking is pretty strongly correlated to familiarity.

dephlogisticated: you are correct that human detection thresholds for many kinds of sulfur compounds tend to be very, very low (for example, nanograms per liter or less, interestingly this is also true for some nitrogen-containing compounds like pyrazines, which can smell intensely of bell pepper, and Trichloroanisole, the musty-smelling compound responsible for cork taint in wine). However, sulfur compounds, in low-ish concentrations, are also responsible for the generally pleasant aromas of sauvignon blanc wine, cooked meat, and garlic. Interestingly, the smell of a particular compound will change dramatically with concentration - ethyl hexanoate, a fruity-smelling ester present in wine, pineapple, banana etc. will, at higher concentrations take on a rotten and cheesy quality. So, yes, we have evolved a biological sensitivity to certain chemical functional groups like sulfur, but this has not, yet, been conclusively tied to innate preference in humans.
posted by zingiberene at 9:18 PM on September 26, 2012 [2 favorites]