Not every feature is useful in determining relationships. Character is collection of mutually exclusive states which have a fixed order of evolution such that each state is derived directly from just one other state. Assume homology, a priori 2. We wish to know if a or a' was the state in their common ancestor. It has a state a, and so we infer that was the state in the ancestor of species 1-4.
Dotted line indicates branching relations uncertain.
4. in event of conflicting evidence, choose phylogenetic relationships supported by largest number of traits. Interpret inconsistent results, post hoc, as homoplasies. Reconstructing phylogenetic relationships between species, then using relationships as a template for explanations of evolutionary origin. Parsimony methods search for minimum-length trees. Order defines the nature of permitted character-state transformations.