[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: a rose by any other name(was fish & dogs)
In a message dated 12/3/00 5:15:02 PM EST, email@example.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.