Phylogenetic trees

Tom DiBenedetto tdib at UMICH.EDU
Wed Feb 26 08:28:26 CST 1997


On Wed, 26 Feb 1997 09:59:11 -0400, Alan Harvey wrote:
>What I find curious is the notion that character polarity (and ordering,
>for that matter) should be done _prior_ to the phylogenetic analysis. This
>is tantamount to saying that we don't know the evolutionary history of the
>taxa (else why would we be doing the phylogenetic analysis?), but we _do_
>know the evolutionary history of the characters that constitute the taxa
>(else how could we provide a priori polarities and ordering?).

Interesting point,,,but, perhaps it is better seen like this,,,by
using outgroups we assert, or assume, that we know both the character
and the taxic history at some particular (relatively high) level of
generality,,,but we do not necessarily know either within the
ingroup.
Character polarities imposed through the outgroup criterea rest on
the assertions that certain taxa are close relatives, and certain
states are ancestral to the ingroup,,,,even though ingroup polarities
are thus determined, one really only is making an assumption about
the condition outside of the ingroup.




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