Posted by:
BGF
at Tue Nov 4 14:20:49 2003 [ Email Message ] [ Show All Posts by BGF ]
>>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.
I don't think 'homologous' means what you think it means. If they have a shared history, they are homologous. That is the very definition of the word. It cannot be convergence if it has a shared history. Convergence is independently developing it (ie bird wing vs bat wing). Not independently applying the same gene. That is homology.
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>>I think you are still laboring under the misconception that the ratsnakes re-acquired constriction.
The constriction gain/regain is not the issue and is actually quite irrelevant to the single origin of venom as the two are not mutually exclusive. What is the point here is that a single lineage has reverted to relying EXCLUSIVELY upon constriction and the utter lack of venom. The other extreme is vipers which rely EXCLUSIVELY upon venom with the utter lack of constriction. Everything else is a sliding scale.
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>>Here is another elementary lesson from S. J. Gould:
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>>"Organisms cannot erase their past. ...signs of ancestry are always preserved; convergence, however impressive, is always superficial."
>>
Thank you, you have now proven our point. The venom is their past and it is not erased. Your hypothesis of convergence is as superficial as your understanding of evolutionary theory.
Please explain to me your multiple evolution of venom and how many independent origins of venom is a more likely scenario than a single origin with a couple losses but no secondary origin in in that lineage. Please also explain your idea that venom independently evolved within a elapids and vipers. Wouldn't there have to be a myriad of non-venomous intermediates? Also, please explain to me how you can go from the non-venomous primative snake, to a non-venomous Elaphe without passing through a myriad of venomous lineages.
Ciao
B
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Dr. Bryan Grieg Fry
Deputy Director
Australian Venom Research Unit
University of Melbourne
www.venomdoc.com
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RE: The Pax-6 gene and the evolution of venom - BGF, Tue Nov 4 14:20:49 2003