hamilcarr:
Curiously lacking was any discussion by Dawkins of the selection pressure that would have set the process in motion and of the selective advantage of members of more than 399 000 generations of their species would have enjoyed as they served as conduits for this ever-invagination, liquid-filled pair of pockets in their head region (Schwartz, 1999: 361-2).
I don't know what event this is referring to but if the writer was familiar with Dawkins's work, he would know that the evolution of the eye was dealt with in his book Climbing Mount Improbable. In a chapter entitled "The Forty-fold Path to Enlightenment" Dawkins discusses exactly how an eye could evolve, shows numerous "transitional" forms, explains exactly why "half an eye" is better than no eye at all, and provides details of a computer simulation that shows how trivial it is for something like an eye to evolve, which is why it has happened so many times in nature.
The quoted writer's idea that 399,000 generations were carrying around large useless eyes just waiting for the last piece of the jigsaw to be added so they could see is absolutely absurd, and one doesn't even need to know much about biology or evolution to see that this is so. It's quite obvious that a creature with light-sensitive cells on its body will survive better than one without (in certain environments, of course). If the area containing those cells is indented, the creature can tell which direction the light is coming from. If the indentation is almost completely closed, only allowing a pinhole of light coming in, the creature will be able to make out individual objects. If the opening is covered by a transparent liquid, a clearer image can be produced. If this liquid can be controlled by muscles, then the creature can focus on objects at different distances. Examples of all these stages exist in nature. At every stage, creatures who have such an eye (or proto-eye) have a survival advantage over those who do not. Every stage can be improved by a single point mutation. That is all that is necessary for a complex eye to evolve.
Walter Gehring provided evidence that only one regulative gene controls eye development. No endless string of links, but only one master control gene.
That would probably be the gene eyeless* or similar. If it is switched on in a group of cells, those cells develop into an eye. If it is switched off or not working, no eye develops. There are obviously many more genes involved in the actual structure of the eye.
*Confusingly, genes are normally named according to what happens when they are malfunctioning. Thus the gene that controls the development of the eye is named eyeless.
