Question

What is the biological rationale for parsimony to use as an optimality criterion the minimum number of changes? Please provide your answer in the form of a written statement.

Answer 1

Parsimony is the idea that, given a set of possible explanations, the simplest explanation is the most likely to be correct. The principle of parsimony in the sciences is used to select from competing models that describe a phenomenon. In biology, it is most often used in the study of phylogeny.
Humans weren’t around when most species diverged, so biologists trying to recreate phylogenetic trees must work from genetics, models and fossil records to determine relationships. In phylogeny, the principle of maximum parsimony is one method used to infer relationships between species. It states that the tree with the fewest common ancestors is the most likely. An example would be hypothesizing that if two species both have prominent incisor teeth they also share a single ancestor, rather than that they evolved the trait independently.
Starting with a set of species and a set of genetic traits, the parsimonious approach would be to look at which traits are shared between species. The tree is constructed by working through the possible relationships for each trait and selecting the option that has the fewest number of state changes. That is the intermediate ancestor species for each trait. The creation of the tree continues until it gets to the root, or common ancestor, for all of the species being mapped.