tree information content & outgroups

Richard Zander bryo at COMMTECH.NET
Tue Sep 16 08:07:20 CDT 1997

Byron Adams wrote:
> My point was that due to the
> process of character polarization (outgroup comparsion, yes, including the
> ontogenetic criterion) the information content of cladograms differs from
> other "tree representations",

The information content of cladograms is as much theory that can be
imposed on them given shared characters of the terminal taxa. The theory
content certainly differs from, say, phenograms.

> and that the choice of a single taxon as an
> "outgroup" can have the dangerous consequences which RZ is referring to as
> a "house of cards."  I think you would agree with me that the "house of
> cards" argument fizzles under rigorous outgroup (and yes, even ontogenetic)
> character polarization.

My point was in chaining cladograms by their outgroups where the poorest
cladogram is the weakest link and poisons the remainder. This is not a
rarity, since some are now constructing Trees of Life with a chaining
rationale. Mind you, I think that such is a fine basis for
classification as long as it is not taken as a "reconstruction" but more
as a "if...then" construction.


Richard H. Zander, Buffalo Museum of Science
1020 Humboldt Pkwy, Buffalo, NY 14211 USA bryo at

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