Hosts infected by viruses found new uses for the genetic
material the agents of disease left behind; metabolic enzymes somehow came to refract light rays
through the eye's lens; mammals took advantage of the
sutures between the skull bones to help their young pass
through the birth canal; and, in the signature example, feathers appeared in fossils before the ancestors of modern birds took to the skies.
Since rabbits have incisors that are excellent at cutting
through many
materials, we find it beneficial to bury the final row of
sutures under the skin so they are not accessible.