[Taxacom] On genera

JF Mate aphodiinaemate at gmail.com
Thu Jul 18 15:05:43 CDT 2013


Thanks Richard, sorry for the delay. It´s not very clear what you mean by:

"... cladistics, because it will not name shared ancestors, cannot infer
monophyly?..."

The ancestor in a phylogeny is hypothetical. With the exception of
incipient species you will never encounter the ancestor. It is gone,
evolved into the other sister taxon. Is this what you mean?

"Suppose we have a bunch of taxa terminal on a clade. Two are most terminal
with shared synapomorphies. The next taxon down, however, clearly, derived
from the same ancestral taxon as the two most terminal taxa. Asserting that
the two most terminal taxa are monophletic splits the ancestral taxon...
Lots of subgenera commonly have some one wide-ranging species of
generalized morphology with some closely related species specialized into
more recent habitats. A theory could be developed if one was not a cladist
that these are all daughter species of the more generalized species."

You appear to suggest that phylogenetics doesn´t make use of plesiomorphic
characters and that it is a bad thing. But lack of change is hardly
informative about relationships isn´t it. Stasis cannot record anything by
definition since it is unchanging. Sure, it can tell you something about
the selective pressures on the taxa but nothing about relationships at that
level. In any case not useing plesiomorphies doesn´t impede I have to be
clear that all data has a phylogenetic signal, the problem is if it is at
the level of interest. On the other hand a phylogeny would not be very
useful if you imposed a given direction on the character state changes.
After all you analyze the data to build a cladogram and in the process test
your hunch. If your hunch is part of the analysis why bother?

"In the first place, I advance a scientific theory, descent with
modification from a species at hand with a clear and known evolutionary
process, specialization into particular habitats. Otherwise, inventing ad
hoc, unnamed and unnameable, invisible explanations for a natural
phenomenon is a step back. The only reason to advance an unidentified
ancestral species is when all the taxa involved are specialized into
particular habitats."

A phylogeny narrows the possibilities in regards to evolutionary direction
but it is hardly ad hoc. You may have a hunch as to how evolution in a
certain group has proceeded (generalized to specialized for example) but if
the relationships are at odds with this scenario you can´t simply dismiss
it or the method as someone´s invention. Either the phylogeny is wrong
(why, do you have outside data that support this) or your hunch is wrong.
Either way you need more data.

Best

Jason



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