BGF wrote:

"What he is saying here here is that at the molecular level they are homolous and that they share a common ancestry and are not convergent. What he is saying is that the trigger has been pulled a few different times. Thus, he is saying that the genes controlling the evolution of eyes evolved once but has been applied repeatedly. Read your own bloody statement."



That is not what Dr. Fernald is saying. He is claiming that the Pax-6, opsin and crystallin are convergent characters. Your concept of homology is flawed. Here is an elementary lesson from Mayr and Ashlock on homology:



"Convergence is usually a superficial similarity of two distantly related taxa: the similar characters are not homologous (Chapters 6 and 10). The wings of birds and those of insects are an example, but so are the wings of birds and those of bats as wings (they are homologous as anterior extremities)."



Like the forelimbs of vertebrates, the Pax-6 gene evolved once. It is homologous at that level. But the Pax-6 genes in the development of the octopus' eye and the fish eye are different derived versions of the same gene and they are not homologous because they have been recruited independently by the chordates and mollusks to control eye development. Either the mollusks or the chordates could have recruited a different gene than the Pax-6. If they did, then convergence is easy enough to ascertain. But it is still convergence if they recruited the same gene independently. The same is true of the wings of bats and birds. The bird wing evolved from the bird forelimb and the bat wing evolved from the bat forelimb. Bat and wing forelimbs are not the same structure, therefore their end products, the wings, are convergences. Mollusk Pax-6 is different gene than chordate Pax-6. Therefore the Pax-6 in the development of their eyes are convergences.



"Obviously reverting to the more primative constricting behaviour was not maladaptive as evidenced by the fact that the snakes have flourished, much as two lineages of sea snake have independently reverted back towards a non-venomous condition.

You really don't have an evolutionary clue do you?"



I think you are still laboring under the misconception that the ratsnakes re-acquired constriction. Greene and Burghardt's study refutes that because they found similarities between the coils of boids, Lampropeltis, Arizona and Regina. Since their last common ancestor is a constrictor, "phylogenetic continuity" is more likely than the less parsimonious scenario of reversal and reacquistion. Some sea snakes may be losing their venom but there is still evidence of a venomous ancestry. The ratsnakes show no such evidence of a venomous ancestry and are therefore more likely to be nonvenomous all along.



Here is another elementary lesson from S. J. Gould:



"Organisms cannot erase their past. ...signs of ancestry are always preserved; convergence, however impressive, is always superficial."

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