The pattern of species in which Pax-6 is involved in eye evolution indicates that it played a role in the development of light-sensitive structures in the common ancestor of modern bilaterians. Sean B. Carroll, Jennifer K. Grenier, and Scott D. Weatherbee (2001) From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design, Blackwell Publishing:Cambridge, MA, Fig. 3.5 pg. 59