Striking a balance, weighting and Cladistics

[Richard Zander]

Well, I disagree, Tom. Simplicity works when you have two clear alternatives
and no real loss if you are wrong. But a Type I error in phylogenetics
(accepting a wrong phylogenetic hypothesis because the null of no support
cannot be falsified) leaves science up a creek.

Take the problem of combining data sets. Suppose you have three terminal
taxa on a rooted tree and these terminal lineages are labeled A, B and C.
The optimal tree is ((AB)C), meaning A & B are better supported than are A&C
or B&C.

Suppose your first data set has A & B sharing 6 advanced characters and A &
C sharing 4 advanced characters. Another data set comes along, with
different characters, and A & B are again supported by 6 advanced characters
but in this second data set A & C  have 5 characters supporting them.

We have a situation with two data sets each independently supporting an
optimal tree of ((AB)C), but the second data set corroborates the
alternative, longer tree ((AC)B) and falsifies the optimal tree ((AB)C). The
combined data sets continue to support ((AB)C).

What do scientists do? Those who use statistical thinking do nothing since
about 50% of the evidence (each character being equal evidence of shared
phylogeny) supports each of two alternative hypotheses (is that statistics
or is it common sense?). This is like flipping a coin.

Those who reject statistics but use philosophy to guide their choices must
often make Type I errors. They almost always get publishable results,
because an exact solution is (philosophically) always acceptable (if only
"poorly supported").

R.


---------
From:
Richard H. Zander
Curator of Botany
Buffalo Museum of Science
1020 Humboldt Pkwy
Buffalo, NY 14211 USA
email: rzander at sciencebuff.org
voice: 716-896-5200 x 351



----- Original Message -----
From: "Thomas DiBenedetto" <TDibenedetto at DCCMC.ORG>
To: <TAXACOM at USOBI.ORG>
Sent: Friday, February 16, 2001 10:36 AM
Subject: Re: Striking a balance, weighting and Cladistics


> I think that the entire history of science argues in favor of this
> perspective. Parsimony is an inherent criterion in much of what we do in
> science (and in every day life as well), and the use of this criterion has
> not inhibited us from confronting and understanding extremely complex
> systems.
> -tom