A plant evolves a high level of poison that enables it to defend itself against insects. soon an insect that prefers to eat this plant evolves an enzyme that breaks down the poison. this is an example of

The answer is coevolution.

Coevolution is a change in one species that results from a change in another species that it interacts with. In our example, a change in an insect results from a change in a plant that the insect interacts with. Since the plant have changed, the insect must change as well in order to survive.