natural units in biogeography

John Grehan jrg13 at PSU.EDU
Mon Apr 26 22:19:01 CDT 1999

>At 08:09 AM 27-04-99 -0400, John Grehan wrote:
>>Peter Hovenkamp's assertion that  "Natural classification" has no meaning
>>in biogeography represents a fundamental difference between our respective
>>I agree that evolution of biogeographic histories is not the same thing
>>as evolution of organisms, but I do not see that more than one context
>>may be applied to evolution.

>You can always use the word "evolution", or "evolve", like in "the
>evolution of the stars", but that does not mean that that all evolving
>histories are isomorphic in the sense of showing a pattern of nested
>hierarchical relationships.

This I can agree with, but this does not translate as justification for
a biological application of synopomorphy being the only possible
foundation for a natural classification, and that natural classifications
are not possible in biogeography.

In terms of a natural classification for biogeography, the application of
natural units in panbiogeography informs us about a shared history
for the origin of different distributions with respect to a specific
geological/geomorphic feature. If a distribution has, for example, a
Pacific baseline, this homology statement allows the hypothesis that the
origin of the distribution has something to do with the formation of the
Pacific (it is a hypothesis just as a character individually identified as
a synapomorphy is a hypotheses). The baseline allows this distribution to
be compared with other distributions sharing the same baseline, and
from thos that do not.

Here the application of natural involves classification according to
hypotheses of a historical relationship between a spatial biological pattern,
and a spatial geological/geomorphic pattern. I would not purport to
know anything about natural classifications of stars.

I think the starting point for vicariance biogeography
>is that if we see multiple sister-group relationships across a particular
>line, we may be justified in thinking that that line is the location of a
>vicariance event.

Interestingly how does one know that a sister-group relationship
crosses a particular "line"? If a taxon is present, for example, in
the Netherlands, Japan, and Columbia (and assume that the biological
relationships are Netherlands-Japan, and then Columbia) and that
several other taxa share the same pattern, what is the spatial homology
of the distribution? How does one determine what geography, out of
all the possibilities, are involved if there is no natural classification

John Grehan

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