for example, all insects are related. they share a basic body plan, whose development is controlled by master regulatory genes. they have six legs; they have hard parts on the outside of the body (an exoskeleton); they have eyes formed of many separate chambers, and so on. biologists explain this with evolution. all insects are the descendants of a group of animals who lived a long time ago. they still keep the basic plan (six legs and so on) but the details change. they look different now because they changed in different ways: this is evolution.