how do living things evolve toxins?

Answer 1

Natural selection says:

1. Living things make more offspring than can survive.
2. These offspring naturally have variations - they are not all alike.
3. Some variations can help an individual survive when other individuals die. The survivor can reproduce.
4. The offspring of the survivor are more likely to have the beneficial variation than offspring from the general population.
5. If this variation continues to help individuals survive, then over time this variation will become widespread in the population.

Some individuals may be just a little different than the rest of the population -- they make a toxin. A predator or grazer feeds on these individuals, but the toxin makes them sick. The consumer doesn't want to eat them any more. The toxic individuals survive, reproduce, and pass on this trait to the offspring. Over time this toxicity is likely to become widespread in the population because the non-toxic ones have been eaten more often. Also, if the toxicity is a factor with survival value, then the population may increase in toxicity over time.