Britannica Sources used in this answer

How does maximum parsimony select a phylogenetic tree?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A diagram showing the tentative evolutionary relationships among hominid species over the past four million years, with skull images and labeled species names connected by solid and dotted lines to indicate proposed evolutionary pathways. — phylogeny Tentative phylogenetic scheme for the evolution of the human lineage. Solid bars indicate the time ranges during which species are thought to have existed, based on fossil evidence. Dotted lines signify evolutionary relationships between hominin species that have been proposed on the basis of the fossil evidence.

Maximum parsimony methods select a phylogenetic tree by identifying the evolutionary path that requires the fewest total number of character changes across all branches. By minimizing these transitions, the method operates on the assumption that the shortest evolutionary path is the most probable explanation for the observed diversity among species.12

When reconstructing these trees, researchers map character states—such as DNA sequences or morphological traits—onto potential tree structures. The tree that accounts for all data with the minimum number of changes is considered the most parsimonious. In cases where certain changes are known to be more likely than others, such as transitions versus transversions in nucleotide bases, parsimony methods can be adjusted to account for these varying probabilities.12

While this approach is a standard tool in cladistics, it is important to note that the most parsimonious path is not always the actual historical path, as evolution may involve independent, parallel, or intermediate changes that do not follow a strictly minimal route.12