More on Biogeographic memory

John R. Grehan jrg13 at PSU.EDU
Tue Oct 16 15:12:53 CDT 2001


>
>Perhaps the confusion is in the use of the word "synapomorphy"? To me, the
>use of the word synapomorphy suggests going all the way from primary
>homology assessment via phylogeny reconstruction to recognizing
>synapomorphies on the preferred tree. I realize that with a more
>restrictive view of synapomorphy ("derived similarity") the whole
>discussion may seem to be pointless...

I have not delved deeply into the philosophical/methodological issues of
synapomorphy in biogeography and systematics so I cannot offer more than my
current understanding of the baseline as a synapomorphic character for
tracks. I would agree that its a subject that could warrant further
evaluation and investigation by those so interested.

>>There is always the possibility that there may be disagreement about the
>>designation of baselines, but to do so one would have to accept the
>>validity of baseline homology otherwise the question is pointless (for
>>example I would not bother to decide among two competing Darwinian center
>>of origin hypotheses).
>
>So in order to disagree with you I'll have to agree first...

There is that danger.

>The basic point of disagreement remains. I would like to let the patterns
>we observe speak for themselves.

I guess I take the view that nothing 'speaks for itself' in a pure
unmodified ideal sense. Patterns speak only in the context of meaning we
give to them. Panbiogeography is one method of giving meaning (information
content) to a distribution pattern (and of course in that process it has,
in my mind, advanced biogeography beyond many traditional approaches).

>Opposed to that, we find John Grehan, who claims that knowledge about
>tectonic features should be used to decide exactly which patterns can be
>compared and which had better not;

I'm not sure I said that - or intended to. Tectonic features provide one
class of topographic-geomorphological features that can be correlated
spatially with tracks. I agree it is a particular criterion for what may be
compared with what and in what way. In this sense panbigoeography is
involved in the sorting of 'informative' and 'uninformative' characters
that is also found in biological systematics.


>To both I say: if either tectonics or ecology is really important, you
>will be able to find traces of it in the result of the analysis.

I think the case is well enough made in panbiogeography.

>To John Grehan: If the Indian Ocean is one tectonic feature,

Actually the Indian Ocean is a geomorphological feature.

>you can expect to find the a single consistent pattern - if it is not, you
>may find different general patterns involving the northern and the
>southern part...

No problem.

>To Pierre: The way across a mountain range may not be the "shortest" way
>to connect two groups of fish - but if it repeatedly turns up between
>different pairs of sister-groups of fishes - then maybe the mountain is a
>relevant feature after all...

I would agree also.

>>Except spatial evidence through baseline homology apparently does not
>>constitute evidence at all in your view.
>(if only I knew exactly what it was...)

So far Hovenkamp's critique suggests to me that he really does have a good
handle on what baseline homology is.

John Grehan

Frost Entomological Museum
Pennsylvania State University
Department of Entomology
501 ASI Building
University Park, PA 16802. USA.

Phone: (814) 863-2865
Fax: (814) 865-3048

Frost Museum
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