More on biogeographic homology

John Grehan jrg13 at PSU.EDU
Wed May 12 07:06:17 CDT 1999

P. Hovenkamp expressed doubt over my perspective on biogeography and
outlined his approach as follows:

>Similarly, when I am correlating taxon- with earth history, I am using the
>best available data for both. If better data turn up for either, I may have
>to think again.

In this procedure, a biogeographic pattern is being correlated with a
geological hypothesis. Since the geological hypothesis is just that,
what biogeographers do is "explain" a distribution on the basis of a
story generated by another discipline (geology). Whether or not the geological
story is good or not, the procedure renders the biogeography (the spatial
pattern) empty of  empirical content - the biogeography itself contains
no empirical data to generate a historical hypothesis.

Geologists on the other hand analyze geological patterns to
generate historical hypotheses. They do not rely on biogeographic
stories about the past to generate their stories.

Panbiogeography is the only method I am aware of (I am open
to correction) where biogeographic patterns are analyzed to
generate historical hypotheses from the distribution data.

>I think that is all fairly normal. Science is fallible, and depends on
>empirical data.

I agree. In panbiogeography the empirical data are distribution patterns. So
panbiogeography has scientific content.

>Somehow it seems to me that what John Grehan wants is an explanation that
>remains correct even if the data it tries to explain is changed.

This was not evident to me.

Hovenkamp states that he does not understand the problem of biogeographic
content. I don't know how many others feel that way, but it represents I
think, an important distinction between panbiogeography and other
biogeographic practices that I am familiar with. In panbiogeography the
distribution pattern - the spatial structure - is seen as informative. As a
parsimony criterion it is necessary to chose a particular spatial structure
out of all those possible. The criterion chosen is minimum distance
as the initial hypothesis.

John Grehan

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