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Darwin Quote (was Paraphyly post)




T.A. and Charles,
I think you are quite right in bouncing George's challenge back to him. He is certainly not alone in making such statements, but I think he is repeating a misconception that is common because of the way cladistics is taught and practiced today. And those who use Darwin to validate this misconception are not taking all of his statements as a whole and in context.
I would urge George (and anyone else for that matter) to read Darwin's comments on classification in Chapter 13 of The Origin of Species. He does indeed state that classifications must be genealogical in order to be natural (on more than one occasion). But he immediately qualifies such statements in the same sentence (and here is a good example):
"but that the amount of difference in the several branches or groups, though allied in the same degree in blood to their common progenitor, may differ greatly, being due to the different degrees of modification which they have undergone; and this is expressed by the forms being ranked under different genera, families, sections, or orders." (Origins of Species, Chapter 13)
He further explains this with a paleontological example. Taken in full context, Darwin not only supports Linnean classification, but paraphyly as well. I think such passages should be required reading for all systematists, so that they will know (as Paul Harvey might say) "the rest of the story".
So to summarize my own view briefly: Synapomorphic information should be given a lot of weight, but strictly cladistic classification and reasoning is too restrictive, often discarding useful information because it is plesiomorphic and/or anagenetic (i.e. degree of divergence), especially the latter. That is why they sometimes will state something to the effect that two bacteria only "resemble" one another and that such resemblance is not due to relatedness. I certainly believe in cladistic thinking to a point, but taken to such extremes I think it is self-deceptive and counter-intuitive in a very real sense when examined carefully (especially when they restrict the meaning of relatedness that ignores plesiomorphy and anagenesis).
------Ken Kinman
*******************************************************
From: "T.A. Curtis" <kodiak@ohmaha.inetworld.net>
Reply-To: kodiak@ohmaha.inetworld.net
To: dinosaur@usc.edu
Subject: Paraphyly post
Date: Fri, 12 Jan 2001 06:33:02 -0800

Dinogeorge wrote:

>No, bacteria A and D simply >resemble< each other more than do bacterium A
>and Homo sapiens C. Homo sapiens C and bacterium D are, however, equally
>closely >related< to ancestral bacterium A (and thus to each other).


      Wouldn't bacteria D be even *further* removed than Homo sapiens C
from common ancestral bacteria A because it had more numerous generational
cycles in between?

      It seems to me that using using time alone to compare relatedness
to a common ancestor--like measuring the distance between two points on a
piece of paper--is inadequate in this case.

      But I'd be the last person to argue with Dinogeorge.  ;-)

      --TAC

T.A. Curtis
kodiak@inetworld.net
13980 Lyons Valley Road
Jamul, CA  91935-2024  USA
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"To a person uninstructed in natural history, his country or seaside stroll
is like a walk through a gallery filled with wonderful works of art,
nine-tenths of which have their faces turned to the wall."
--Thomas Henry Huxley
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"We ought to make the pie higher." -- George W. Bush

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