Neil Shubin and Sean Carroll discuss homeobox genes, a set of genes that produce basic body parts in all animals. In 1994, Walter Gehring discovered the eyeless gene, which guides formation of fruit fly eyes. As an experiment, Gehring put a mouse's eyeless gene into a fruit fly, resulting in normal fruit fly eyes. The same holds true for homeobox genes for wings, legs, even heads. This discovery indicates that animals descended from a single common ancestor that passed along to them a set of homeobox genes, used to build a wide variety of forms from just a few basic body plans. From Evolution: "Great Transformations."