Why humans smell bad and kill grass with feces

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Emmveepee

Registered Senior Member
I tried to make the topic interesting ;)

I hear that rotting human flesh smells much worse than rotting animal flesh. Is there any truth to this? Why is that?

I also hear stories of human feces killing plants (such as grass). What causes human feces to kill grass, while manure replenishes it?

Just a 'Intro to Biology' college student here, be nice ;)
 
Feces from almost any animal, in large enough amounts, will kill grass. Animals that have high levels of nitrogen in their feces, like dogs or humans, will kill grass because the levels are toxic.
Where cows defecate on grass, the manure will actually smother grass, since the manure is mostly tough-to-digest cellulose, which is the major ingredient in plant.
 
Humans have much more variety to their diets, where animals eat almost the same thing every day. Maybe that has something to do with the bad smell?
 
There may be several things as to why shit smells bad. Biologically, it's toxic to us, so it'd make sense if it was really gross, because it's dangerous. It's also dirty– full of harmful microbes and pathogens and parasites.
Smelling like shit is both a sign of being dirty and potentially infectious.
There's probably a cultural thing associated with that, where smelling like shit's a sign of barbarism or lack of civility.
 
Roman said:
There's probably a cultural thing associated with that, where smelling like shit's a sign of barbarism or lack of civility.
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...and the fact that it is physically repulsive. Cultural thing or not bad smell is great deterent.
 
Sarge,
Nothing smells intrinsically bad. Flies love the smell of shit. I'm just postulating about why it smells bad. Just as eating cow intestine, or rat, or dog may sound repulsive to you, fecal matter's repugnance to us may be much stronger than it once was.
 
Seriously - you do not know how much the generation previous to sanitary reforms lived in the fecal matter of their cohorts. Shit is not actually that much to be afraid of - especially your own. The most it will tend to contain is bacteria that are already living in the flora of your intestines. However, when humans moved into urban (and even suburban) situations, that drastically increased the need for sanitary conditions for sewage - increasing the probability of encountering a dangerous pathogen.

Because the population density for dogs is much, much lower than that for humans, the likelihood that they will encounter a threatening bacterium from other dogs' feces is very low. In the high population densities that humans now live, it is not only likely but inevitable despite the omnipresence of antibiotics. We are all just waiting for the airborne transmissable phase of a virus like HIV (or Ebola, or any maladaptive virus).
 
But more importantly, why do we smell worse than a dead animal after death?

I ask this because we were talking about the black plague, and someone brought up that humans smell worse dead than animals. Being the aspiring biologist that I try to be, I set course to find the cause of this!

Thanks for the help.
 
Well the problem is that a "smell" is subjective and therefore cannot be measured quantitatively. So perhaps one person thought that the human smelled much worse, whereas another thinks the animal smells worse. I am by no means a biologist and have limited knowledge on the subject but it still seems to me that what i said should be valid. Is there a general consensus that humans smell worse after death?
 
I hardly believe there is one. Rotten flesh essentially smells the same, especially as the main components (tissues etc.) are not significantly different between humans and, say, pigs.
The bad smell from feces is heavily influenced by the diet and the bacterial composition in the respective guts.
 
The question should be, why does the smell of rotting human flesh smell worse to _humans_? Perhaps because something that kills one human might kill another human so evolution has programmed a strong olfactory aversion? Just a thought.
 
Well could be, though I sincerely doubt that it is the case. Rotting pork smells roughly like human (though with all the disinfectants it is sometimes hard to tell), rotting fish is really awful, though distinctly different and so on.
 
Primates do have different amounts of bacteria present than other species. Most noticably in our mouths. If you get bitten by a human you almost always get a nasty infection. If you get bitten by a dog you get nothing. If you want to see how bad we smell without all our hygeine go to the zoo. The monkeys always smell the worst and thats basically what were closest to.
 
But I bet the monkeys dont think they smell.

If we sat around our own poo all the time wouldn't we become used to the smell?
 
The smell of excrement is very important to animals. The NGO in their noses can detect lots of infomation about that animal be the waste.

For example, they can tell if that animal is related to itself and helps avoid any in-breeding that could occur if it mated which would reduce the gene pool.

Any decomposing of any animal is going to smell bad to us as we are told by the smell that it is dangerous. Most animals around us are smaller, in the UK. Such as mice and dogs, cats and other pets. We are much larger and the space for bacterium to grow is much bigger. You would have to go to a farm and smell a dead decomposing horse or cow to compare the smell.
 
Frisbinator:
Dogs eat their own fecal matter, I'd like to see someone explain THAT.
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My theory, insecurity.
I've noticed that among all dogs, meaning a ton of neighbour's and my own, its the females and beta males that roll in the shit.

So it would be something like a human smearing itself in cosmetics to enchace its own beauty and hiking its chance for acceptance.
Therefore, the insecure canine will smear in feces to enchace not its beauty but smell, hiking its chance at acceptance?


On topic:
Remeber the baby years.
We played in our own shit, I even ate some.

Point benig that this repulsion to feces is learned.
 
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