Human and ape phylogeny

Ren� Zarag�eta i Bagils rzb at MNHN.FR
Fri Apr 4 17:39:13 CST 2003

I agree with John Grehan's arguments. But I should not focus only on this

- Molecular characters are NEVER polarized (so they are phenetic, in
Grehan's sense)

- The more general problem is that Farris' optimization (= cladistic
computer programs) is flawed. Cladistics is supposed to be a way of testing
a conjecture (initial hypothesis) of hierarchical relationships. However,
Farris' optimization produces no hierarchies, but unrooted trees (something
that some Americans call "networks"). There is only an isomorphism (~
equivalence) between rooted trees and hierarchies. So an outgroup is needed,
not because of cladistics, but because of Farris' implementation of
cladistics used in computer programs.

- Farris' optimization is flawed in (at least) another sense: if your
hypothesis proposes a grouping of, say, animals having a tail, your computer
program may tell you that there is a group characterized by... ABSENCE of
tail. However, you never made this hypothesis. It is your computer program's

There are other problems with Farris' optimization.

A solution, nevertheless, exists: three-taxon analysis.


René Zaragüeta-Bagils
Département Histoire de la Terre UMR 8569
Equipe SICC (Systématique, Informatique, Cladistique et Chronologie)
Muséum national d'Histoire naturelle
8 rue Buffon
75005 Paris - France

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