genetic vs morphological trace of phylogeny

[John Grehan]

At 09:00 AM 4/13/2004 -0700, you wrote:
>At 08:16 2004-04-13, John Grehan wrote:
>>It seems that what you are saying is that you are right any 'explanation'
>>you provide is obviously explanatory and the failure on my part to adopt
>>your position is therefore my fault.
>
>No, I'm saying that you routinely pass off a lack of understanding as a
>difference of opinion.

This could go round and round. It is possible to suggest the contrary, that
you pass of a difference of opinion as a lack of understanding.

>I don't expect you to adopt my position. I expect you to support your
>position with arguments. You have done that well with the morphological
>evidence, but rather than addressing the molecular
>evidence, you have discounted it, and claimed support by certain cladist
>authorities.

Not quite. I have presented arguments, but I would agree with you that they
have not been made in detail - something that I might do in the future
(e.g. the sequence alignment problem). Conversely, responses have largely
been of the assertion kind also. Also, I have not 'discounted' molecular
evidence - I have questioned its veracity as a necessary predictor of
phylogenetic sequence.

>He continued to argue, in an uninformed manner.

I guess this is the crux. At this point one could argue that Curtis has not
presented anything more informed than I. This kind of rhetoric is relative
to one's perspective. Perhaps I am 'uninformed' in supporting
panbiogeography also since I am in the minority position on that.

My 'uninformed' opinion aside - Caccone and Powell (Evolution, 1989) note
the following:

  "Virtually all molecular phylogenetic studies, including these, have a
major underlying assumption: the genetic similarity of difference among
taxa is an indication of phylogenetic relatedness. Lineages that diverged
more recently will be genetically more similar to one another than will be
lineages with more ancient splits"

They also say:

"This assumption cannot be tested with absolute rigor, as we can never be
absolutely certain about the correct phylogeny of any group, just as we
cannot be certain bout any historical event. However, two facts lend
powerful credence to the assumption. First, virtually all molecular studies
are in perfect accord with phylogenies deduced by other methodologies. For
example, the molecular data are in excellent agreement with all other
evidence indicating that humans and African apes are each other's
relatives, followed by orangutans, gibbons, and the Old World monkeys."

Comment welcome. I hope the irony is obvious.

John Grehan

Dr. John Grehan
Director of Science and Collections
Buffalo Museum of Science
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http://www.sciencebuff.org/biogeography/Panbiogeography/Panbiogeography-Gate.htm
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