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Jonathan,
Firstly, apologize for misspelling you're name
(my senior bio tech was a John Wagner and it just kinda stuck in my
mind)
>>As long as we are splitting
hairs...
It seems that everything, especially everything classificatory, comes down to this eventually. :) The point of my entire last two posts on this subject is that this is a semantic nightmare. >>>George
has further pointed out that determining whether a reveral
(sensu cladistica) is "genetic" or "convergent" may be impossible. I agree strongly with this assertion. George says that some "reversals" are actually convergences. This results from his acceptance of either the definition given above, or the definition of a "genetic reversal" as the true defintion of reversal. This is indeed why the "cladistic" definition of reversal is an operational defintion, not an explicit invocation of an evolutionary process. We cannot know always what processes were afoot (sorry) in the re-evolution of the four-toed therizinosaur pes. >Well, using the operational
definition, "reversal" is the correct
term regardless Seems I have done us both a diservice. The
intention was an apparently poor attempt at support for you're conclusions re:
the need to understand the operation definition of "reversal", while
attempting to illuminate some reasons why the definition must be operational
(i.e." we would hardly expect a complete return to the "original"
form of the character... with a different starting position in overall
morphospace...and is under different selection pressures"). You correctly
summed up Georges points re: limitations of the term reversal. And, as we both
pointed out (I just did a really poor job), irregardless of the limitations of
the term, the operational use of reversal, must and will continue.
>>We cannot know always what processes were afoot
(sorry) in the
re-evolution of the four-toed therizinosaur pes Where we differ...
Perhaps one day as more is understood of the
genetic mechanisms that drive evolution within extant populations, we will be
able to ascribe either "convergence" or "reversal" to
particular speciation events in the fossil record. If the fossil record of a
particlar clade is particulary complete, we should be even to hazzard an
"educated" guess as to the magnitude of the selection pressure (in
genetics breeding programs known as the Intensity of Selection).
>>If you wish to examine this question
further, by all means do so.
I truly believe that some of the puzzles in
paleontology will only be done so employing information gleaned from Neontology
("downward transfer of information").
>>Indeed, our catagorization
of these processes seems to be largely a construct of our imagination rather than recognition of real phenomena. >> Never said better. Even our defintion of a species is somewhat
of a construct. In my opinion, this is one of the attractions of
paleontolgy (somewhat like techie cryptozoologists!) Given the constraints
of the fossil record, this is why I respect paleontolgists so much- the ultimate
in puzzles!
Sorry about the long snips and for the confusion,
Walgreens Telecommunications Dept.
Network Analyst/Database
Design
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