A hypothetical ‘escape and radiate’ example of coevolution, with a host-plant evolutionary tree, or phylogeny, on the left and an insect-herbivore phylogeny on the right. Red arrows: insect species feeding on a particular host. Stars: the origin of a novel anti-herbivory defence (in plants) or counteradaptations to overcome these defences (in insects). Different colours represent radiations with the new adaptations. Speciation occurs first in the plants and then in the insect herbivores (based on Ehrlich & Raven 1964 and Futuyma & Agrawal 2009).