[Taxacom] Paraphyletic groups as natural units of biological classification

Curtis Clark lists at curtisclark.org
Thu Oct 2 23:36:56 CDT 2014

On 2014-10-01 11:09 PM, Stephen Thorpe wrote:
> That was uncalled for! I was trying to articulate an idea. If my terminology wuz in some way inappropriate, I apologise, but it was entirely unintentional.

Sorry, but "plesiomorphic species" rubs me the wrong way. Characters (or 
more precisely character states) are plesiomorphic.

> Let me rephrase it in the form of a question: do you think it is common (or even possible) for a monophyletic group (M) to evolve quickly (within a larger monophylum), leaving only a remainder of plesiomorphic species which are very similar to each other, but very different to M?

This is not an issue of science, but of terminology. Since monophyletic 
groups are monophyletic, they have a single ancestral species, so we're 
talking about speciation when that species splits from whatever. The 
residue of species in the (now paraphyletic) group made by the exclusion 
of your monophyletic group will of course have similarities that the 
monophyletic group doesn't share. They are called plesiomorphies; that's 
what the word means. Any time a species forms, it leaves behind a 
paraphyletic residue of whatever monophyletic group you choose.

Curtis Clark        http://www.csupomona.edu/~jcclark
Biological Sciences                   +1 909 869 4140
Cal Poly Pomona, Pomona CA 91768

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