A guess as to how lifeforms evolve defensive toxins (i.e. become poisonous):
Being poisonous doesn’t benefit an individual animal much; if you taste bad, a predator might give up in the middle of eating you, but you’re still hurt and likely to be attacked by another predator.
However, genes are selected for only in terms of the animals that do reproduce; a poisonous animal can make its kin, who share the relevant genes, more likely to reproduce in a few ways:
Many insects, like ants, have only a few individuals responsible for reproducing; the metabolic cost of producing poison makes worker ants less efficient, but reduces how many get eaten, and it has little effect on the queen (who probably won’t be eaten regardless).
Healthy animals are in general less likely to be attacked and far more likely to successfully reproduce than unhealthy ones; the poison pushes a few more animals into the ‘unhealthy’ category, but makes all the animals less attractive to predators. If the poison isn’t very costly, it should be able to spread by chance up to the point where this is effective in small populations. (Healthy animals can generally afford a modest additional cost to avoid predators; stotting is a behavioral equivalent.)
Much of the metabolic cost of a poison is in compensating for its negative effects in your own body; if you’re consuming a poisonous animal regularly, it’s cheap to reuse its poison. (Poison dart frogs do this.)
More costly poisons would presumably evolve over time from weaker poisons, in the same way that other defensive features are exaggerated over time.
A guess as to how lifeforms evolve defensive toxins (i.e. become poisonous):
Being poisonous doesn’t benefit an individual animal much; if you taste bad, a predator might give up in the middle of eating you, but you’re still hurt and likely to be attacked by another predator.
However, genes are selected for only in terms of the animals that do reproduce; a poisonous animal can make its kin, who share the relevant genes, more likely to reproduce in a few ways:
Many insects, like ants, have only a few individuals responsible for reproducing; the metabolic cost of producing poison makes worker ants less efficient, but reduces how many get eaten, and it has little effect on the queen (who probably won’t be eaten regardless).
Healthy animals are in general less likely to be attacked and far more likely to successfully reproduce than unhealthy ones; the poison pushes a few more animals into the ‘unhealthy’ category, but makes all the animals less attractive to predators. If the poison isn’t very costly, it should be able to spread by chance up to the point where this is effective in small populations. (Healthy animals can generally afford a modest additional cost to avoid predators; stotting is a behavioral equivalent.)
Much of the metabolic cost of a poison is in compensating for its negative effects in your own body; if you’re consuming a poisonous animal regularly, it’s cheap to reuse its poison. (Poison dart frogs do this.)
More costly poisons would presumably evolve over time from weaker poisons, in the same way that other defensive features are exaggerated over time.