For many years evolutionary biologists have examined animal eyes anatomically, and concluded that there was "convergent evolution" between the eye of vertebrates and the squid. They seemed so similar in their design and function, yet were connected by no chain of phylogenetic relationships that indicated a common origin. However, with the improvements in identifying genetic codes, and then sets of linked genes that, together, controlled the development of complex structures, the genetic basis for eyes has been identified. As it turns out, there is captivating evidence that can be interpreted that the origin of eyes was only once, and all eyes -- insects, vertebrates, ... all eyes -- are modificaitons of a common genetically coded plan. Where eyes do not connect, the genetic potential seems present. There may be many genetic potentials that are not usually expressed in an organism.
This summary article is taken from Science News, issue of May 10, 1997.