follow up on paraphyly / polyphyly

[Dr. James Adams]

Derek,

>Monophyly: a natural group
>
>Paraphyly: a natural but incomplete group
>
>Polyphyly: an unnatural group

Ah yes.  I was waiting to see this.  Actually, it ain't bad.

I believe "natural" in this context means including the ancestor;
"complete" means including all descendents.

For instance, most people know what you mean when you say reptiles -- this
includes several extant lineages, and also many extinct lineages, including
the "initial reptilian ancestor" (whatever that was), but *not* all of the
descendents -- hence, reptiles are paraphyletic.  If it was monophyletic,
then a hairy reptile typed this, and feathery reptiles are flying past my
window.

I don't personally have a major problem with using paraphyletic groups, as
long as we understand they are paraphyletic and define them as such.

On the other hand, if you were to group birds and mammals together in a
classification, this would be polyphyletic, as there is no common ancestor
for just these two groups that you can point at, without going into the
reptiles.  You can't include the ancestor for this grouping because there
*isn't* an immediate past common ancestor.

This is how I was taught and understand the terms -- let me know if this
does not make sense.

James


James K. Adams
jadams at em.daltonstate.edu
Phone: (706)272-4427
FAX:  (706)272-2235
Visit the Georgia Lepidoptera Website:
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Also check out the Southern Lepidopterists' Society Website:
    http://www.southernlepsoc.org/