Answer
Heterochrony causes the natural differences in how organisms look over the course of their lives due to the progressive expression of a particular developmental program. Heterochrony changes the relative timing of parts of development and, thus, produces variation in body form.
Work Step by Step
Review the discussion of heterochrony. Note that it does not involve mutations which alter a particular body part but rather changes in timing. To see how this changes body form, imagine if you had gone through puberty but some important secondary sexual characteristic had only appeared twenty years later.
