Britannica Sources used in this answer

Why can the most parsimonious phylogenetic tree sometimes be incorrect?

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.

The most parsimonious phylogenetic tree—the one requiring the fewest evolutionary changes—is not always correct because biological evolution does not necessarily follow a minimum path. Several factors can lead to inaccuracies in this method:1

Independent Changes: Evolution may involve independent changes along different branches, or changes may occur through intermediate steps that are not captured by a simple model.1
Reversals and Parallelism: A trait may change from an ancestral state to a new one and then revert back to the original state in a specific lineage, or the same trait may evolve independently in different lineages through parallel evolution, creating the appearance of a shared ancestry where none exists.1
Unequal Probabilities: Not all evolutionary changes are equally likely. For instance, in DNA, transitions (purine to purine or pyrimidine to pyrimidine) occur more frequently than transversions (purine to pyrimidine or vice versa). If a model does not account for these varying probabilities, it may misinterpret the evolutionary history.1

While maximum parsimony is a useful tool, it relies on the assumption that the simplest explanation is the most likely, which may not hold true in complex biological systems.1