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Re: Selective Extinction

There's a sort of null hypothesis I've wondered about for some time.  Its
not even a speculation, since I have no fixed idea what the explanation
might be.  Could extinction be related to genetic make-up per se,
independent of specific ecological factors?

The reason I ask is that we frequently hear about this or that clade going
extinct as a whole during mass extinctions, despite the fact that the clade
contains numerous species with all kinds of niches.  Dinosaurs are, of
course, the best example, but there are surely others.  The KT extinction
may be a bad example since there are a number of pretty good ecological

I suppose I should be more forthright.  I do have a class of agents in mind:
some viruses and prions are thought to cross species boundaries, and some
more conventional parasites as well are not very host-specific.  However,
there are limitations on this ability which would tend, even in the case of
(e.g.) some incredibly adaptive super-virus, to restrict the contagion to
species that have some basic genetic similarity.  

I'm not sure how one would test for such a thing.  I suppose that I would
expect to see ecologicly and geographically diverse clades going extinct for
no apparent reason *outside* of mass extinctions on a fairly regular basis.
Does this occur?

  --Toby White