Take caterpillars for example: if a bird eats a fatally poisonous caterpillar and dies immediately, it learned nothing, the caterpillar gained nothing for being poisonous, and that caterpillar species will continue to be preyed upon.
But if a caterpillar is only mildly toxic, and a bird eats it, the bird may survive and learn to avoid things that look like it, and that caterpillar species as a whole benefits as the cycle continues.
Am I missing something obvious? Wouldn’t it make more sense for mild toxicity to prevail as the more advantageous trait, over time?
edit: another point of confusion — more toxic animals tend to advertise their unsavoriness with bright colors. We generally accept that predators know to avoid brightly colored prey, but if they die during their very first encounter with one, how is that info passed along to other predators?
In: Biology
Variation in the initial predator population means some will try to eat the poisonous prey and some won’t. The ones that do will die. Now you are left with a population less likely to try to eat poisonous prey.
You might wonder how the poison evolves since the prey gets eaten and can’t reproduce. For that, you must understand genetics the way Dawkins lays out in The Selfish Gene. We tend to learn in school that organisms reproduce, so everything is about organisms and organisms just *have* genes.
That is not the right perspective. It is the gene that reproduces. A gene for being poisonous will randomly turn up through mutation. Initially it will have no effect on survivability, so it will obey genetic drift: it will randomly be snuffed out by chance, or wind up spread through the population. When the latter happens, it is finally widespread enough to cause selective pressure through what was discussed above. So now you have predators that avoid these poisonous prey, because the poison was a selective pressure on *them*. This means the poisonous prey are not preyed on as much, which means having the poison is now a selective pressure on *themselves*, so it is a selected trait and will become increasingly common in the population.
Actual learning from experience is entirely unnecessary.
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