Phylogenetic evidence

Robert Mesibov mesibov at SOUTHCOM.COM.AU
Wed Jul 10 10:45:40 CDT 2002

Tom DiBenedetto wrote (inter alia):

"Phylogenetics is thus equal to the discipline of historical systematics - the
enterprise of erecting classifications of species based strictly on their
relationships... I recognize that geography might well add
to the details of the evolutionary narrative - but my concern is with the
question of
what is to be considered valid evidence of relationship - phylogeny."

This is very interesting, and it suggests that Tom & I are never going to
see eye to eye on certain issues. Tom is clearly saying that he is mainly
interested in the historical relationships between taxa. If he hears about
a human family, all he wants to know is who married whom, and who is whose
children, so that he can draw up a family tree. He isn't as interested in
where people lived, or other non-relationship details of the family
history. Fair enough, and I agree with Tom that unadorned relationships are
necessary and sufficient for a natural classification.

However, I'm personally interested in more than the unadorned
relationships. I want to try to understand how, when & where evolution has
actually worked in particular groups. (OK, I admit it: in millipedes, but
the same could be said for any group.) Relationship information isn't
enough, I need other evidence, and much of it comes from biogeography and
earth history (landscape evolution). For Tom's enterprise biogeographical
data might come in handy if used judiciously in a few special cases; for my
enterprise such data are absolutely essential.

Another philosophical difference lurking here is how you view the
evolutionary narrative. If you think 'species' and relationships between
such objects, you're naturally led to focusing on the properties of
'species' and how to use those properties to understand the relationships
between 'species'. If like me you think 'lineages', you think more
architecturally about tree structure, i.e. the relationships between
objects with the objects removed.

I'm not sure how these two views can best be contrasted. Maybe with
phylogeographic results? If I learn that certain genes have distributed
themselves in differing and spatially biased ways through parapatric
populations of two 'species,' I'm fascinated and I start thinking about how
this might drive the next evolutionary event, and how it might have
happened in the past to give the genetic/biogeographical picture seen in
some other lineage. Tom, on the other hand, might get a creepy feeling
about all this introgression and start worrying about whether the 'species'
concerned are in fact the solid objects he imagined. Or he might not worry
at all, since at some level of taxonomic and geographical generalisation
these details are irrelevant to the bigger picture of 'blurred' taxa and
their 'blurred' relationships, which is essential for a workable

Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
(03) 64371195; 61 3 64371195

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