Parsimony, likelihood, and simplicity

GOLOBOFF, PABLO A.

CLADISTICS (PRINT)

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2003 vol. 19 p. 91 - 103

0748-3007

The latest charge against parsimony in phylogenetic inference is that it involves estimating too many parameters. The charge is derived from the fact that, when each character is allowed a branch length vector of its own (instead of the homogeneous branch lengths assumed in current likelihood models), the results for likelihood and parsimony are identical. Parsimony, however, can also be derived from simpler models, involvingfewer parameters. Therefore, parsimony provides (as many authors had argued before) the simplest explanation of the data, or the most realistic, dependingon ones views. If (as argued by likelihoodists) phylogenetic inference is to use the simplest model that provides sufficient explanation of the data, the startingpoint of phylogenetic analyses should be parsimony, not maximum likelihood. If the addition of new parameters (which increase the likelihood) to a parsimony estimation is seen as desirable, this may lead to a preference for results based on current likelihood models. If the addition of parameters is continued, however, the results will eventually come back to the same place where they had started, since allowing each character a branch length of its own also produces parsimony. Parsimony can be justified by very different types of models? either very complex or very simple. This suggests that parsimony does have a unique place among methods of phylogenetic estimation.