Ever notice how most animals (specifically mammals) seem to be able to do #2 without needing anything like toilet paper to keep clean? A lot of animals’ excrement comes out as neat, fairly dry fecal pellets. Even those that don’t often seem cleaner than human excrement. What is the reason behind this? How come the creature that is so evolved as to be able to communicate in speech or through writing, through media such as television and the internet, and to be able to build technology that has the potential to destory the planet, has not likewise evolved a neater, cleaner excretory system compared to those of many mere brutes? Does it, for example, have anything to do with our varied diet compared to those of animals?
Herbivore crap seems less offensive to me than carnivore poop in general. Adding to the human ick factor is sheer volume. I suspect the degree of gut fermentation and bacterial flora affect the disgustingness.
I am reminded of the time our cocker spaniel found and rolled in a big pile of unmistakably human shit during a park outing.
It was not a pleasant ride home in the car.
There’s the interesting fact that because humans walk upright, we are the only mammal that has to wipe its ass. Most mammals, the anus is not buried between two hefty muscles masses that can help smear the output. (Except maybe sheep, but then bulky wool is a recent human-induced characteristic) Perhaps our hands evolved in tandem with upright walking so as to be just long enough to accomplish this task?
Therefore, a protruding anal ring is not necessary because we have the hands to accomplish this task well enough. In evolution, usually whatever is “good enough” is the solution.
As for ick factor, #2 runs the gamut from wet cowpies to dry rabbit pellets. The animals that have to hide their position tend to have the tidier output.
At the other extreme, the hippopotamus can’t hide (except underwater) and has extremely untidy output.
Look at the things we find most revolting: human poop, vomit, the smell of dead humans.
All things that it makes obvious evolutionary sense for us to avoid. Especially poop, where we’d have ample opportunity to come into contact with it every day, if we didn’t have such an instinct.
WRT other species, it seems to largely depend on how close to us they are. Dogs and pigs may eat a pretty similar diet to us, and we find their faeces pretty much as disgusting as our own.
Species with very different diets to us, like herbivores probably have substantially different gut bacteria and so their waste probably emit fewer (or a lesser quantity) of the the chemicals that our noses have evolved to detect.
Oh and I know some species don’t avoid their own poop, that could be a problem for this hypothesis. I can speculate on some reasons why that would be, but I don’t want to pile up too much speculation.
And we’re off.
But now you’re just leaving us to speculate on what those reasons my mean, and to speculate on your reasons for not wanting to speculate on those reasons.
Well the reason is, I thought I’d give people a chance to disagree or find fault with the speculations that I did outline, first.
So that’s at least one of the speculations you listed cleared up 
It makes sense, yes; evolutionary sense : I don’t know what that is.
Bonobos and Chimps are the closest (I think) evolution wise to humans. And they play with / eat their poop.
So if it is a evolution thing, it must be fairly recent.
Who says animals don’t need a good butt wiping? Never seen a dog or cat scooting their butt along the ground? Maybe you’ve never seen it, but I’ve seen a brown trail on the carpet after my dogs that that. That’s their toilet paper! Ewwww…
Also, our Maltese would occasionally have dingleberries. “Hey, why is there a brown spot on their white butt?” Ohhhhh…
Being omnivores, our poop varies greatly on what we eat and in what quantities. We tend to eat more than necessary and may change our diet to “move things along” if we get off our regular schedule. Animals, both wild and domestic, don’t monitor their poop schedule. They eat if they’re hungry and feel good, don’t eat if they don’t feel well, and generally* poop when necessary, not to stay on schedule.
*I['m] amaze[d] that some pets, especially dogs can stay on schedule if trained to wait to go out for their walk(s).
Wild animals digestive systems are more efficient at absorbing more nutrients from what they eat, since they don’t know when they might eat next.
As md-2000 stated, prey animals may have firmer, less smelly poop to prevent betraying their presence.
Edit: Another thing about animals, at least with our dogs, is that they don’t have a sense of “Hey, that stuff I ate gave me the runs. I shouldn’t eat it again!” They seemed to live by, “It tasted good going in, that’s all that counts!”
A couple more thoughts.
Animals that can, will lick their butt. Why? Because it itches! That’s their toilet paper!
Also, back to the (particularly) prey animals hiding their presence. Dogs and I’m sure other animals will lock their babies butts to hide their scent and keep their area clean.
When our Mama dog had pups, she’s lick them to stimulate their BM, then clean them up. Then she’s come to you wanting to lick YOUR face. Oh dear girl, I love you, but not that much!
What it means is that it makes sense for us to not see a pile of poo or vomit as a lovely meal, as the probability of it causing illness or infection is very high. Individuals that have such an instinct will have tended to survive and reproduce more successfully.
Not quite that simple actually. In the wild, chimps don’t really throw poop. And the fact they do it in captivity may be because they find it disgusting not a refutation of that.
From the same cite it does mention that some species of howler monkeys may throw poop in the wild, though doesn’t elaborate on whether that is a sign of annoyance or playfulness.
However, in general, if you just search for “faecal avoidance” on google scholar there are many papers on many, many species, it’s a very common trait.
Now it’s true that some species do eat their own poop to continue to digest some foods that still have not been fully digested. They still may find other individual’s poop repellent. This is why I didn’t really want to get into the weeds of talking about different animal species.
But, in terms of humans, there is a strong correlation between what we find disgusting and what things were in our natural environment* that could make us sick. So it’s not too surprising that, to us, our poop is among the most disgusting substances of all.
* If our natural environment had included very strong radioactive sources, they would probably stink to us, or be repellent in some other way (to whatever sense could be most easily retconned to detect ionizing radiation). The whole town of Chernobyl would stink. 
I take it, then, you have no actual first-hand experience with bovine excrement? Cattle poop is semi-liquid to soup.
As for the rest of creation - most wild animals do not have access to junk food which, in addition to not being good for general health, does not lead to pretty poop, either. (Seagulls in fast-food restaurant parking lots being a notable exception, and their poop ain’t nice.)
When human beings eat healthy diet high in fiber our poop tends to be “neat” and tidy, if not “dry fecal pellets” at least a minimally messy sausage-like extrusion. We may still feel a need to wipe, but it’s not nearly as bad as it could otherwise be.
Rabbits eat poop. Rabbits produce two different types of poop, one of them intended for eating. They do this to extract more of the nutrition from their food, and also to obtain nutrients like B12 produced by gut bacteria towards the end of their digestive tract, which is a bit awkward as the bits that absorb B12 are towards the other end - hence the eating of fecal pellets. Rabbits get sick if they don’t eat their poop.
Interesting. Could this account for the error made by the Bible that classifies rabbits among the animals that chew the cud?
ISTM that when animals eat the food nature intended for them, their scat doesn’t smell so objectionable. I’m not so offended by human scat produced by fruits, vegetables, and high-fiber grains. Different story for pizza and chicken wings washed down with a glass of whole milk.
I mean, cow shit isn’t exactly delicate floral notes, but to me it smells mostly like cow and fermented grass, unless they’re corn-fed on a feedlot. Conversely, domesticated dogs eat mostly processed food, and I suspect this is why I find dog shit just as offensive as human, if not more so.
I am not an expert in this area and do not want to jump to conclusions based on a few Google searches.
For example, Google may find you contrary research based on your search terms :
Researches find poop-throwing by chimps is a sign of intelligence
@Mijin : feel free to respond to the above, but I’d also like to hear from some experts in this field.
This begs for a double-blinded research trial with computer software to help grade expressions of disgust. And since people vary so widely in their appreciation of aromas*, you’d need a sizable test panel. I would need to be paid well to serve on it.
*Right now our Amorphophallus konjac is blooming, with its delectable and fly-attracting scent of carrion. Some people apparently faint dead away at the aroma, but I find it…interesting, especially in concert with the neighboring gardenias.
I acknowledged this in the post above yours.
The point is, that in general, species find things repellent / disgusting that are harmful to them (indeed this is probably the only reason to even have a feeling of physical disgust in the first place).
So a rabbit is not going to find its own poop disgusting. But humans do.
But of course there is no objective sense in which any poop is worse than any other.
Contrary to what? It seems consistent with my cite.
Cats also do that. Yeah, I’d rather change diapers, but that’s how our different species evolved.
Koala pups also get the intestinal bacteria required to digest their diet of eucalyptus leaves from eating their mothers’ stools.
Humans evolved to be omnivores, so everything is fair game.
https://www.google.com/search?q=have+humans+always+been+omnivores&rlz=1C1ASVC_enUS940US940&oq=have+humans+always+been+omnivores&aqs=chrome…69i57.8632j0j4&sourceid=chrome&ie=UTF-8
That said, post meat eating poop is one of the smelliest: To digest foods high in sulphur such as meats, garlic, dairy, broccoli, kale and cabbage, your gut has to work overtime. This produces a lot of gas, which makes the poop smell bad. These foods, even if the digestion works fine, can make your poop smell bad.
Edit: Two of the three things you mentioned that may cause smelly poops is dairy, which people who are lactose intolerant like me have a problem digesting as mentioned in the article I linked above.