Dr. Fernald of Stanford University writes:



"Paired eyes in the three major phyla, vertebrates, arthropods and mollusks (fig. 4), have long been considered to be classic examples of evolutionary convergence. At the macroscopic level, this must be true since they arise from different tissues and have evolved radically different solutions to the common problem of collecting and focusing light. However, as discussed above, opsin has a significant DNA sequence homology across all phyla. Remarkably, recent work by Gehring and Ikeo [9] has shown that features of ocular development in different phyla can be coordinated by a homologous 'master' gene, Pax-6. That a single gene could trigger construction of an animal's eye in diverse species led to their proposal that eyes are monophyletic, i.e. evolved only once. This is an interesting hypothesis that goes against all the previous suggestions of multiple (i.e. polyphyletic) origins for eyes. There are several reasons why this hypothesis seems difficult to support. It is well known that Pax-6 organizes other structures besides eyes and is even necessary for the onset of various actions outside the nervous system. Also, other genes can cause development of eyes [reviewed in 10]. Whether eyes are monophyletic or not, the work of Gehring and his colleagues has stimulated a great deal of new work on eye evolution, which is a good thing in itself. Clearly, eyes have common molecular constituents whether they be opsins, Pax-6, or others. Yet, homology at the molecular level of organization does not predict homology at the organ or organismic level. Molecules are not eyes."



Paraphrasing Dr. Fernald, "Molecules are not snakes." Snakes need to feed and reproduce. A snake that hunts for active prey simply has no reason to abandon venom. Such a change is maladaptive. Maladaptive changes simply do not occur in nature because of natural selection and competition. Maladaptive changes may makes sense on a diagram on a piece of paper, but it does not make sense in nature.

[ Show Entire Thread ]