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Re: a rose by any other name(was fish & dogs)



In a message dated 12/3/00 5:15:02 PM EST, kinman@hotmail.com writes:

<< I think a good middle ground is to reject a formal taxon Pisces, but 
"fish" is a natural group as long as someone doesn't try to throw something 
like whales in with them. >>

Actually, once we have well-defined clades, >any< Boolean-arithmetical (or 
set-theoretical) combination of them also constitutes a well-defined group. 
In this example, we have clades Vertebrata > Tetrapoda > Cetacea, so the 
group "fish&whales" is well defined as Vertebrata - Tetrapoda + Cetacea. Good 
taxonomists recognize that there is no point to stringing together long 
combinations of clades into "taxa" (regardless of how much their members may 
resemble one another), since this just recreates the problem that well-placed 
paraphyletic taxa exist to solve.

I think it would be a good idea to reject outright any taxa constructed as 
Boolean-arithmetical combinations of clades that are disconnected. In the 
above example, Cetacea is disconnected from Pisces by Tetrapoda, so under the 
connectivity rule the group "fish&whales" cannot be a taxon. This is, of 
course, a dogmatic rule--but a practical one.