This involves co-evolution where prey and predator evolve together. A caterpillar becomes poisonous and then a certain bird learns to not eat it. The bird may have trouble telling the difference between poisonous and non-poisonous caterpillars. The poisonous one may change color to help the bird tell the difference between the 2. The non-poisonous one uses camouflage while the poisonous one choses a different color which may be a bright color. It doesn't consciously choose a color, but it is easier to understand when I phrase it that way.

Their strategy to survive is not to hide or be strong but to be poisonus. Unfortunately it doesn't help you much to be poisonous when something else ate you already. So for most of them it makes sense if they can be recognised easily so that the next of their species won't be eaten again.

As predators learn the difference between lookalike poisonous and non-poisonous races/species, the difference in the poisonous ones might become more pronounced (the less different ones being mistaken for harmless more often). See how the Samurai Crab came to be.

The “why” comes down to evolution. Let’s do a thought experiment. There is a population of caterpillars that are poisonous. They look exactly like a non-poisonous species and both are mostly brown. Birds will try to eat both. They notice that some taste great and some taste awful.

Which is which though? You don’t want to make the same mistake twice. There is, of course, genetic variation in coloration. Some of the poisonous caterpillars have small, thin red stripes and some don’t. The birds eat both and notice that all of the ones with red stripes taste bad but only some of the all brown ones taste bad (because some are poisonous and some are the non-poisonous species). They stop eating the striped ones but keep eating the brown ones (and spitting them out). The poisonous ones with no red stripes are thus weeded out of the gene pool and all of the poisonous offspring now only have red stripes. Over time, those red stripes get larger and larger as the caterpillars with bolder red stripes are less likely to accidentally get eaten and thus the genes for bold bright warning colors are more likely to be spread in the gene pool of poisonous animals. The opposite is true for tasty non-poisonous animals. Only those with the best adapted camouflage survive to pass their genes onto the next generation.

Another aspect not mentioned yet: As a poisonous species, you outnumber the predators. There will be enough of you to reproduce even while some are being eaten (and taking their predators with them). So camouflage isn’t part of your survival strategy as a species. You’re then free to use colors for other things such as mating markers.

Compare this to a non-poisonous prey species which can’t deviate from camouflage colors without risking being wiped out.

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Creatures evolve randomly in some aspects and in other aspects they don’t. This is a random evolution. It may have started with the color change and then they were easily seen and easily eaten until one evolved to be poisonous or it may have started with the poison and then the color change which is more likely in my opinion. If caterpillar bob evolved to be bright red randomly then all the caterpillar bobs would just be a buffet for the birds until another random evolution occurred and caterpillar bob now has poison in his system. Eventually the birds associate caterpillar bob with pain or sickness and stop eating him.

More likely caterpillar bob already had poison and then evolved the bright red color. I’d be already had the poison then being easily spotted by the bird isn’t a big problem because the bird won’t consider him food.

Milk snakes evolved to look like coral snakes. They aren’t venomous like the coral snake but they benefited by looking similar to an animal no other animal wants to play with. It was a random evolution with a big up side for the snake.

An example of non-random is the giraffe. Newer evolutionary theories say that the giraffe stretching its neck up to reach the higher leaves in the taller trees contributed to its neck growing longer.

An additional cool detail that can help understand that this is not a coordinated mechanism but a matter of selection, is that sometimes the non-poisonous/venomous species will evolve to look exactly like a poisonous/venomous one. Plenty of insects that take the color scheme of wasps, for example. This is just because the individuals in a population that most closely resemble a wasp (due to mutations that happen over several generations) are less likely to be eaten by predators that fear wasps and so are more likely to reproduce

This ☝️ is the best answer, most of the others end up being teleological or anthropomorphic arguments.

An interesting since note is that once a boldly coloured hazardous population is present with its selective predators there is often a secondary evolutionary selection for any mutations that leads to other species beginning to resemble it.

Thus the possible evolution of non-stinging Hover Flys with bold black & yellow stripes that closely resemble those on wasps.

Being poisonous, itself, is not super beneficial to the specific animal. It's good for the species cuz anything that's about to start eating your kind will die, but it still requires that first sacrificial lamb.

So a second level of defense is advertising. Hey, look at me. Yeah, there's no way to confuse me for another animal. I'm definitely the poisonous one. Don't even try it, I would rather us both live than us both die. Go eat Frank over there.

Yes, selection can also cause two hazardous species to end up looking like each other as negative interactions with either species is beneficial to both. Monarch butterflies and Viceroy butterflies are an example.

The example you cited with hover flies is Batesian mimicry while the butterfly example is called Müllerian mimicry in case someone wants to learn more.

Thanks for that, just reading through wikipedia on this, I love how the selection pressure is population sensitive. In that if the mimic starts to predominate over the model the whole thing falls apart.

Newer theory about neck stretching? Makes no sense, giraffes born with a longer neck can reach higher on the tree thus they are more likely to survive and pass on longer neck genes.

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That’s true too. But the new theory is that giraffes who stretch their necks are more likely pass on those genetics.

Oh, I see, it's not the stretching of the neck that affects the evolution, but the behavior of reaching higher that gets passed on.

Evolution is all about what genes get passed on overtime. The passing of genetics is directly tied to a creature's ability to reproduce. Reproduction is tied to survival. An animal that stands out like a sore thumb (i.e. is colorful) is very easily noticed by other animals. If that animal is somehow not getting killed before they can reproduce, then they are either the apex predator or the predators of that region have no interest in eating them (i.e. are poisonous), so they can continue to pass on the colorful gene.

I think the above covers all the good points, so I’ll only add the types:

• Batesian mimicry is when another organism mimics the warning something else gives without possessing the trait being warned about. Example is a hover fly with black-yellow stripes like stinging insects while possessing no sting.
• Müllerian mimicry is when multiple species adopt the same warning signal while possessing similar traits. Example is how many stinging insects all utilize black-yellow or similar striping patterns.
• Mertensian mimicry is similar warnings among deadly and non-deadly threats. Mainly because the warning can’t be learned if every experience is fatal, so the non-deadly are the method of associating the cue with the warning.

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I find this answer the most explaining, yet it's missing one thing.

People speak like, predators can learn what to eat and what not to eat, like with taste. But it has nothing to do with this. Because, the learned experience cannot pass to new generation. It would require the poison to be non-fatal, and the species of predator would have to be intelligent enough, so they could teach it. And still, some variants of predators might just try and like the experience, due to having mutations on their tasting receptors. So, how did they co-evolved?

Probably, once upon a time, predators who hunted those creatures varied by their instinct or senses of hunting creatures with specific shapes or colors, and those who liked eating colorful things died more and more often due to colorful preys containing more and more fatal poisons. This led to survival and production of those more who don't prefer eating colorful preys, and those who are more colorful "preys" (they are actually not preys anymore at this point).

Yet, time to time some mutations can give arise to the old variants of predators who liked to hunt colorful creatures, but they would keep dying, so their population in the pool would be neglected. On the other hand, if some mutations would create a "prey" that are colorful yet not poisonous now, it might increase its number in the genetic pool easily for at least some time due to predators not eating them anyway. But such mutations must be rare, and variants on the predators' side might eventually balance things back to this current state.

So, it may have a secret wave function in the background, which, things tend to converge towards this current state every time they deviate a little, rather than going the opposite direction, due to the path on the opposite direction being way longer compared to the current state of things (that is colorful being fatal). So, things must have been kinda locked down into this state.

Last but not least, it's amazing how it's not even about only one species of prey and one species of predator, but among many species of preys and predators. It must be due to many species hunting the same prey, and many species being hunted by the same predator.

By the way, everything above is kind of my prediction of how things happened and keep happening.

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That does not explain why non poisonous caterpillars does not get more colorful over time

The non-poisonous ones that are least flashy and best at hiding are the ones who survive to reproduce. Their offspring will continue to pass down those traits.

Thanks for adding that. Regarding the Mertensian mimicry, is the non-fatal threat really needed? Whatever predator is eating this prey would also have genetic variations which dictate which foods they go after. Those with a proclivity for eating the fatal prey would die off; those without would pass on that aversion.

This would also be true for poisonous caterpillars, they also could increase their chances to survive if they get or stay inconspicuous (hide better)

But if more of them are surviving because they have visual warnings against being eaten than are surviving because they are good at hiding, those visual warning genes will dominate in the population.

Yes but we do not have data about that. Also, non poisonous caterpillars could increase their chances of survival if they develop the same flashy pattern as the poisonous ones

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This does happen! Sometimes! Small populations or small portions of larger populations will begin looking like their inedible counterparts over time. The problem with this - inedibility isn't a perfect defense. A few inedible individuals will still get eaten and spat out. If the markers that signify inedibility become less reliable (as in, there are greater numbers of edible mimics), then the selection pressures of "don't eat the red striped caterpillars" will weaken, and the selection pressure to be a mimic will as a consequence also weaken. Like parasite - host population trends, this leads to an oscillation between a greater number of mimics and their relative collapse, depending on the specifics of the situation.

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Inherently, you are correct about “the dead don’t breed” and thus it would eventually be conveyed generations down the road to absolutely never touch those things. And in either circumstance, being BRIGHT AND OBVIOUS to potential predators right now is a huge disadvantage. That disadvantage is massive if the trait banks on “the next generation is less likely to eat something like this”. Genetic memory isn’t an ideal value compared to the cost, while showing relevance to a non-deadly warning would be adopted faster. And it benefits the non-deadly variety since both warning routes receive selection pressure. Every event is potentially a usage of defense material (venom), injurious, or fatal, so even snakes with deadly venom are benefitted through avoidance rather than needing to expend the venom.

I think that's a decent theory but it might have a big problem. If non-poisonous animals start to resemble poisonous ones, then the selection pressure for looking poisonous goes away, as there's only a limited amount of food out there and predators will inevitably realize that some of the colorful prey are tasty as well.

So if the Hover Fly evolution theory is true, then you have to either go with the assumption that food scarcity just isn't enough to push animals back towards older behavior, or you can assume that this trend towards colorful poisonous animals comes and goes in cycles.

Maybe the answer is that Earth's biodiversity reached some kind of equilibrium in the past and the number of new, colorful yet non-poisonous species equals the number of new, poisonous yet colorless species. So the generalization of "colorful animals are poisonous" is always true enough.

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Can you please somehow relate how an octopus may mimic a number of different things in terms of an ecological “language”?

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This does happen and it happens not infrequently.

It is an evolutionary strategy called Batesian mimicry

If I had to guess, I’d say that the ones with vibrant colors had a much better survival rate, and in addition, probably developed secondary purposes as well like attracting mates. These mates would eventually make the connection to survival.

Beneficial traits alter entire courses of species. Sorry I’m on the move typing this.

This certainly makes the most sense.

The color is a disadvantage, but is overwhelmingly compensated with numbers AND killing off predators with the 'eat colorful' trait, which in turn removes the 'eat colorful' trait on local predators.

The colorful poison species might take an initial dip in population, but predator species quickly lose the predation trait from the natural selection pressure of the poisonous species.

Yes, as someone else put it here about Betesian Mimicry the mimic will reach only a minority of the models population because it is becomes dominant the pressure goes away.

that's another hypothesis, we can't know much, the problem with evolution is that there are so many things we can't reproduce it on laboratories that we are not able to provide a answer to a why-question.

For example we don't know why we have long beards and long hair and we have to cut it, we are the only kind of animals whose have certain parts of our body with hair length that is not self regulated

Isn't that an example of Natural selection, I learned about it I. 7th grade, had to do with moths if I remember correctly, the brown ones that camoflauged with trees started appearing more than the white ones

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Wait, but why do all of the ones with red stripes taste poisonous?

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There is no definitive answer to this question. Some scientists believe that poisonous animals tend to be more colourful as a way to warn predators of their toxicity, while others believe that the bright colours of these animals are simply a result of natural selection and have nothing to do with their toxicity

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Yes, it is natural selection. You probably learned about the peppered moth in school. Pretty famous example. https://en.m.wikipedia.org/wiki/Peppered_moth_evolution

Basically the area was so polluted with soot during the industrial revolution that the dark form of the moth was better adapted to survive on the dirty surfaces in town.

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Thank you, this topic is interesting stuff

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Some developed a poison by chance, and that trait was selected for, as it made predators less likely to eat them.

Uh, no. That’s not “newer theory” you are talking about Lamarckism which was debunked a long long time ago. Stretch your neck all you want, it isn’t going to change your DNA and there is. I way to pass that to your kids genetically.

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