>>17498
>I mean I heard that some inspects eat toxic plants to accumulate toxin in itself. So that's a result of million years of evolution.

I don't understand fully how this is "started". As far as I know, mutations coulnd't be very serious or subject will die, so process must be slow. For example, some snake gets very lightly toxic substance in saliva for some reason. If it gets more, it could die from own toxin.

Or same thing with horns, non-horned animal couldn't easily grow large horn in few generation, it must be slow thickening of bone that will result in horn in million years.

But these small steps aren't good for survival. If some cow has slightly more thick head bone, it doesn't really increases survival chance - there is much more random things like muscles etc, so this bone factor wouldn't be noticed. It would give preference to subject only when it grows much more. And mutations happen in random, so there will be no trend to increase that factor.