follow up on paraphyly / polyphyly

Michael A. Ivie mivie at MONTANA.EDU
Wed Nov 10 18:39:52 CST 2004


Derek,

Clearly from the question, I too have trouble teaching the difference between
paraphyly and polyphyly to students ;-)

The Wiley method of referencing the inclusion or exclusion of the most recent
common ancestor seems to work when accompanied by a discussion of simple
character state-changes, but would be very difficult when the example is
something with a large amount of homoplasy, such as a molecular data set.  In
fact, in that case, it may be impossible to tell them apart because you cannot
say what was the state at the base of the tree (i.e. the condition of the most
recent common ancestor).  Try the illustration that in paraphyly, a branch
"sticks out"  from the lineage to make a group different from the bush left
behind, vs polyphyly, where branches "stick into" the group from multiple
lineages to form the group-bush, and include reference to the most recent
common node that leads all terminal taxa involved.  However, you will note that
even very talented and bright students sometimes have trouble with this.

Mike

"Dr. James Adams" wrote:

> 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:
>     http://www.daltonstate.edu/galeps/
> Also check out the Southern Lepidopterists' Society Website:
>     http://www.southernlepsoc.org/

--
__________________________________________________

Michael A. Ivie, Ph.D.
Department of Entomology
Montana State University
Bozeman, MT 59717
USA

(406) 994-4610 (voice)
(406) 994-6029 (FAX)
mivie at montana.edu




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