Phylogenies and uncertainty

Steve Heydon slheydon at UCDAVIS.EDU
Fri Jul 28 08:52:40 CDT 1995


>I also agree that there is a vast difference between 10% completely correct
>trees and 10% correct nodes of a tree.  Kim et al. 1993. Evolution 47:
>471-486. have shown that in their simulations about 55% of the nodes are
>correct.  As I have tried to indicate in a previous message, even if we know
>that a certain percent of the tree or nodes of the tree are, on average,
>correct, we don't know which ones they are.  Such a tree is close to useless,
>in my opinion.
>
>-Warren Lamboy

Perhaps this only means that we have a statistical problem of a slightly
different nature. Certainly a node defined by one apomorphic character is
less likely to be "real" than a node defined by three or more characters.
For all its problems, techniques like Bootstrapping do provide such
information. Other statistical techniques comparing phylogenies of the same
group derived with different kinds of data sets would also provide
information on the amount of support for different nodes. Perhaps what we
need is actually more phylogenies.

It should not be forgotten that sciences other than systematics tolerate at
least as much statistical uncertainty as we do. Is anything really proven
statistically in ecology or animal behavior? Even such hard sciences as
physics are built in part on the Heisenburg (sp.?) principle which states
that we can never know exactly both the position and the vectors of
movement of subatomic particles at the same time. (Or something like that.)
There is an excellent chapter on curiosity in a book by Scott Peck called
Further Along the Road Less Travelled which eloquently treats this whole
subject area.

Being close to the truth is not the same thing as being ignorant.

Steve Heydon
slheydon at ucdavis.edu




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