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I was thinking about how some animals emit sounds, and then wait for the sound to bounce back to their ears letting them detect other animals to eat as well as obstacles to avoid. Some animals in the ocean also emit light that they use to help them see prey. I was thinking of an animal that similarly throws scents and waits for those scents to get reflected back by other animals and object in the environment. I know smell uses molecules, which are particles, while hearing uses sound waves, and vision uses electromagnetic waves. Still I was wondering if an animal could evolve to put smells into the environment and then wait for the scents to get reflected back?

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    $\begingroup$ One imagines a nervous teen boy about to go on his first date, anxiously checking his breath by breathing into his cupped hand then sniffing it. $\endgroup$
    – Boba Fit
    Nov 17, 2022 at 0:46
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    $\begingroup$ Honestly, I'm not a fan of "Can X evolve?" questions. On the one hand, given enough time, anything can evolve. On the other, nothing like this has evolved, so there's no evidence it can. Such a creature would have trouble on any world that experienced wind or precipitation. But the creature is mega cool! Do you want help developing the creature for your imaginary world? We'd love to help. Otherwise, what's the point of the question? $\endgroup$
    – JBH
    Nov 17, 2022 at 3:49
  • $\begingroup$ Can you say how that might work, or why not? $\endgroup$ Nov 17, 2022 at 18:26
  • $\begingroup$ "The Tersurons, long-dead natives of the planet the action takes place on, communicated through farts. They became extinct when they discovered fire." $\endgroup$
    – Michael
    Nov 17, 2022 at 22:50
  • $\begingroup$ Perhaps and what would happen if the wind was in the wrong direction? $\endgroup$ Nov 19, 2022 at 18:29

6 Answers 6

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This is comparing apples to oranges. Smells do not reflect off of surfaces.

Sight and hearing measure waves. Smells don't come in waves.

Even so, imagine that a creature would throw a stream of particles around and try and measure their return. Consider the energy costs of doing that. It is much cheaper in metabolic costs to use bioluminescence, sonar or even an electric field like some fish do, if you are going for an active sense.

The closest you can get that involves secreting matter to detect prey, predators or mates is spider webs. They lay their silk and get feedback from it, but its vibrations on strings rather than smells.

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  • $\begingroup$ @AC is that a real creature? Googling for it I only find articles about mythology. $\endgroup$ Nov 19, 2022 at 1:21
  • $\begingroup$ @JBH oops, you got me $\endgroup$
    – A C
    Nov 19, 2022 at 3:33
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Most unlikely to work.

Firstly, scents only tend to travel downwind so scent molecules emitted by your creature are unlikely to return to them.

In principle you could spray a liquid upwind and rely on the breeze to return it to you but it would be a very short range solution - probably only a few metres. 'Seeing' something via the returned scent would also be problematic - if you coated an object in a scented liquid then the amount of scent molecules flowing back downwind wouldn't tell you much about the object. In principle, you might be able to tell if something was moving from side to side or approaching you, but I doubt it would be very effective. If the thing you were attempting to detect approached upwind you would be screwed, as would be the case if the creature moved downwind towards you but faster than the relative wind speed.

There is also teh issue of resource. You can't 'throw' a few scent molecules any distance - would need sizable droplets or a spray. So the creature would either be spraying a constant flow of liquid upstream or would spend most of its time blind.

Almost certainly better (and more likely evolutionarily) to develop/rely on organs that can detect sound, vision, heat, vibration, etc and use scent passively.

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Let's decompose what you're looking for. We'd have to assume that the creature was constantly emitting a cloud of the stuff, like a musk. If it were chemically distinct from one creature to another, it could be used to identify the creature's territory, and where they've been.

Anything beyond that would require a differential in partial pressure between one side of the creature's sensory apparatus and the other. Put into English, more stink one direction than in other directions. If you consider the speed of diffusion of flatulence at standard temperature and pressure (about 8 inches per minute). If you compare this to 1100 feet per second, or the speed of light, then at best you could get a general feel for "something in that direction," with no physical detail.

The one use I could imagine for this would be for an endurance hunter, like wolves and humans. The creature would hit its prey with a glob of spit, then follow it until the prey stopped to rest.

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    $\begingroup$ The "glob of spit" idea is brilliant. Step 1: Evolve a predator that relies on smell to hunt (well, that already exists - all cats and dogs do that). Step 2: Evolve a prey that relies on its absence of smell to evade the predator. I don't think that exists in our world; animals tend to have strong body odour. I don't know how hard it would be to evolve a mechanism to hide your own body odour, but let's assume a species evolves that does that. Step 3: Evolve a predator that spits at its odourless prey to make it more smelly. $\endgroup$
    – Stef
    Nov 17, 2022 at 10:11
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    $\begingroup$ I could be wrong, but is this not similar to how the Komodo Dragon hunts? It attacks a large prey animal and leaves its venomous (or toxic?) saliva in the wound so that it can follow the scent while the toxins/venom bring down the prey $\endgroup$ Nov 17, 2022 at 10:48
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    $\begingroup$ Or for tracking mates. $\endgroup$
    – Pablo H
    Nov 17, 2022 at 14:55
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    $\begingroup$ @stef I believe that big cat and deer mothers (and likely other mammals) heavily groom their young to reduce their scent to make them harder to detect. $\endgroup$ Nov 17, 2022 at 16:09
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    $\begingroup$ @RobertRapplean It's venom, not bacteria. nationalgeographic.com/animals/article/komodo-dragon-venom $\endgroup$
    – nasch
    Nov 17, 2022 at 17:07
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For the question as asked, no. However...

Scents are unable to be used as analogous to sight or sound, primarily due to the speed differences involved. Scents rely on diffusion pressure to spread. You can get into some gritty detail with this. Alternatively, scents spread through convective pressures as well.

Some of the answers mention wind being a problem. Wind can actually help dramatically if the wind is very turbulent and not traversing very quickly over larger scales. Think farting in front of a fan. The fan is mixing the air in the room, but not moving new air into the room or old air out of the room.

Even if the scent travels quickly, the issue is the inability to differentiate the reflected scent from the emitted scent. With sound, you emit a pressure wave from your mouth. Your ears hear transmitted through your skull as well as directly from your mouth. That sound will travel and hit a wall and reflect back as an echo. If your yell is continuous, you may not hear the echo at all. It is far easier to hear the echo if you yell in short bursts when you're no longer emitting noises prior to the reflected sound coming back. For a smell to work similarly, it wouldn't work like smells at all. Smells diffuse from higher density to lower density at a rate too slowly to create a return pressure wave that can overcome the diffusion pressure from the source. Even releasing the smells in bursts doesn't overcome the scent lingering around the source.

However, maybe your creature doesn't care about the smell it emits, which isn't just a single scent. No, this creature is super stinky. It emits all sorts of scents. Why? Because the scents themselves aren't meant to be reflected. The creature is producing volatile compounds of various sorts. Think of something along the lines of pheromones. Some that react specifically to its favorite prey. Some that react to various types of rocks. Some that react to various types of plants. Once the volatile compounds touch their intended target, it changes slightly, giving a slightly different scent than what the creature produced.

It is the altered scents your creature is interested in and uses.

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    $\begingroup$ I love the creative solution you suggest: that the "scent" chemicals emitted react with interesting things, and the creature can smell the reaction products. $\endgroup$
    – minseong
    Nov 18, 2022 at 15:15
  • $\begingroup$ @theonlygusti Although you would have to wonder why you don't just smell the scent of the target directly. $\endgroup$
    – DKNguyen
    Nov 18, 2022 at 18:41
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    $\begingroup$ @DKNguyen In this manner, the creature could smell things that don't emit their own scent or try to mask their scent. In certain environmental conditions, some things wont emit a scent at all unless you get it wet. So it might be looking for a dried up crusty flower seed in a desert. $\endgroup$
    – David S
    Nov 18, 2022 at 18:59
  • $\begingroup$ @DavidS That's true. It would need to be something that normally doesn't give off a scent. $\endgroup$
    – DKNguyen
    Nov 18, 2022 at 19:19
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This is, in one sense, already a thing. Star-nosed moles use a similar trick to smell underwater, which mammals can't otherwise do. This trick doesn't require direct contact with a chemical source, useful for protecting sensors, and probably good since you want range, not the obvious tell of a bubble smashing into you, which could alert prey.

Also worth noting is how insects, like bees and ants, use chemicals to communicate or coordinate attacks, how pirate perch achieve invisibility, the fact various prey animals actually roll around in sensory sources, while predators track prey or use scent to aid in prey detection.

So the key here, imao, is to create an environment where an unusual method of smelling works (as with star-nosed moles, who could not otherwise scent aquatic prey), or where chemical signals aiding in marking and tracking prey, and then you're golden!

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Yes, absolutely, it is possible.

The animal may emit some kind of reactive substance that will react with those objects that under normal conditions do not smell, and release smells that can be detected.

Maybe acid fumes? or some organic solvent or corrosive agent that will react with different surfaces and produce different volatile substances

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