[Taxacom] Monophyly is testable?

Bob Mesibov mesibov at southcom.com.au
Sat Apr 4 06:02:29 CDT 2009


Unfortunately I am going to be in the field this week and I won't be
able to keep up with this thread on TAXACOM, but I saw your post in the
TAXACOM digest today and was very surprised. You said:

"Monophyly, on the other hand, is a clear, testable criterion. The
testability then leads to the second point. It makes systematics a
hypothesis-testing endeavor, i.e., real, hard science, and thus takes it
above the purely descriptive level."

I think you need to explain this. I can only see two senses in which
monophyly could be tested. One is to compare a hypothesis of monophyly
with the real evolutionary history of a group. Unless you have a time
machine or a fantastically good fossil record, that's just not possible.
If you retreat to the argument 'How else could it have happened?', you
are arguing ad ignorantiam, which isn't hypothesis-testing.

The other, everyday test is to weigh up the evidence *for* monophyly of
a group and *against* monophyly of a group and make a judgement. This is
far from real, hard, hypothesis-testing science.

I am also surprised that you don't see description as a
hypothesis-creating activity. If I describe a new polychaete worm and
refer to certain structures as metanephridia, I am hypothesising a whole
string of anatomical and physiological tenets, not to mention implying
homology with similar-looking structures in other polychaetes (please
excuse the obscure example - it's late in the evening here). Each of
these descriptive hypotheses can be tested.

In an earlier TAXACOM thread I pointed out the difficulty in finding
ways to *test* a phylogenetic hypothesis without relying on data already
used to create that hypothesis. I recommend you read Kirk Fitzhugh's
papers and comments on TAXACOM, which formalise the nature of the
thinking that goes on when we define 'species' and evolutionary

We do not do 'real, hard science' because we can't. Unless we ignore
evolution entirely and work only with non-systematic classifications,
what we are doing is historical research, and history does not lend
itself to hypothesis testing a la physics and chemistry. We infer and we
hope for the best.
Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery
and School of Zoology, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
Ph (03) 64371195; 61 3 64371195
Webpage: http://www.qvmag.tas.gov.au/mesibov.html

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