homology in biogeography and biology

P.Hovenkamp Hovenkamp at NHN.LEIDENUNIV.NL
Thu Sep 23 10:21:17 CDT 1999

I'm sorry that the message that sparked off this thread was unintentionally
Anyway, some clarification has emerged in the meantime about the meaning of
"homology" in panbiogeography:

At 09:24 PM 22-09-99 -0400, John Grehan wrote:
>>Please note: it is not simply "similarity of features" (or as Richard
>>Jensen wrote: "a similarity reflecting common origin"), it is
>>similarity of features *as a result of common ancestry*.
>Agreed. this was implicit.
>>But this seems to leave out the notion of descent from a common
>>ancestor, which is at the heart of our understanding of homology, and
>>has been for a very long time.
>Again, this was implicit. Sorry I should been explicit.
> Homology has a
>>much more restrictive meaning than just similarity.
>Agreed. In panbiogeography the homology is a common history or origin

and John stated in an earlier message:

"In panbiogeography any two distributions sharing the same
geological/geomorphic feature (i.e. their tracks both cross this
feature) may be said to be homologous with respect to that feature. The
constitutes a biogeographic character present in those distributions."

Thus I arrive at the understanding that in Panbiog "homology" refers to
"the same feature found in different distributions, as a result of descent
from a common ancestor" (this is, mutatis mutandis, the concept of homology
as formulated by Tom DiBenedetto, following Eldredge and Cracraft).

This raises the following points:

1. Do distributions "speciate"? They need to, if the concept of common
ancestry  is to be applied.
2. Are the features of distributions heritable?

If there is only the slightest doubt about either of these points, I tend
to agree with Tom that using the word "homology" is just conceptual inflation.


P. Hovenkamp
Rijksherbarium, Leiden
The Netherlands
hovenkamp at rhbcml.leidenuniv.nl

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