biogeographic homology

P.Hovenkamp hovenkamp at RHBCML.LEIDENUNIV.NL
Wed May 12 10:24:29 CDT 1999

At 10:31 PM 28-04-99 -0400, John Grehan wrote:
>Peter Hovenkamp's response concerning the distributin of a hypothetical
>taxon represented in the Netherlands, Japan, and Columbia illustrates the
>contrasts in methodology and application of homology concepts in
>The first issue concerns level of differentiation. I am inclinded to agree
>if a taxon is apparently undifferentiated between these localities, a recent
>establishment of the range is a likely possibility. However, there have been
>cases where such distributions have later been shown to actually comprise
>distinct species so some caution is required.
>Hovenkamp responds to the qeustion of how to determine what geography
>is involved by correlation of the taxonomic ordering of the component
>taxa with (1) each other and (2) earth history.
>The question that remains is what earth history? How is the choice to be made
>from biogeographic analysis. In most if not all cases of phylogenetic
>this invovles a preference by the athour that a particular earth history is
>true (earth history is, after all a story or theory about the past which may,
>or may not, be true to an entire or partial extent). If the postulated
>matches, a shared history is considered a likely possibility.

I think all this illustrates a rather different (in my opinion, confused)
view of how we work in everyday science. What I'm trying to do (sometimes)
is to find an explanation for the data at hand. If the data change, I may
have to change the explanation. So, if it is no longer a unitary species of
which I am studying the distribution, but a species with locally
differentiated populations, my explanation may change. How could it be
otherwise? Do we have to stick to an explanation in the face of the
evidence? Or do we have to hedge our explanations against all possible
revised data?
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.
I think that is all fairly normal. Science is fallible, and depends on
empirical data.
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.

>The trouble with such approaches is that there is no biogeographic input or
>orientation of the distribution. The distribution is seen as uninformative
>the probable geographic sector involved. Instead, preference is drawn from
>external disciplines such as geology. It is my view that such approaches
>biogeography non-scientific since the biogeography itself is not assigned any
>empirical contnet (i.e. the spatial structure of the distribution is itself
Frankly, I don't understand this at all.

P. Hovenkamp
Rijksherbarium, Leiden
The Netherlands
hovenkamp at

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