Parsimony

Parsimony is a fundamental principle of phylogenetic inference. By parsimony, the phylogeny of a group of species is inferred to be the branching pattern requiring the smallest number of evolutionary changes.

Phylogenetic inference using parsimony proceeds in two stages:

1. Infer the unrooted tree for a set of species. An unrooted tree shows the branching relations between the species but does not show the position of the deepest common ancestor. It is a phylogenetic tree with the time dimension removed.

2. Locate the root. This means calculating character polarity for a group: finding the shared derived homologies which reveal whether A evolved from B or the other way round.