What does monophyly mean?
Monophyly is a technical biological term for the condition in which a group of organisms includes a common ancestor and every descendant of that ancestor. Such a group is called monophyletic and represents a complete evolutionary branch. The concept is central to cladistics, where classifications are evaluated according to shared ancestry rather than superficial similarities in appearance or behavior. Monophyly can therefore show that organisms with very different features are closely related, as in the case of whales and hippopotamuses, while also revealing that a superficially uniform group may have arisen from multiple evolutionary lines. The opposite condition, polyphyly, describes a group that combines separate branches and does not include their most recent common ancestor’s full descendant set. Monophyly is thus not merely a label for a group’s appearance; it is a claim about evolutionary history that can be tested using anatomical and genetic evidence.
nounIn evolutionary biology, monophyly is the condition of a group containing a common ancestor and all of that ancestor’s descendants. A monophyletic group is therefore a complete evolutionary branch, rather than a grouping assembled from organisms with different origins.
- In evolutionary taxonomy, the property of a group being composed of a common ancestor and all of its descendants.
"The classification of whales as a monophyletic group supports their close evolutionary relationship with hippopotamuses."
"The researchers tested the monophyly of the genus by comparing DNA sequences from several species."
"The apparent resemblance between the two animals did not establish their monophyly because their ancestors were not the same."
Monophyly asks a deceptively simple question: does the group include the entire family tree of its common ancestor?
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does monophyly come from?
Monophyly combines the Greek prefix monos, meaning “single” or “one,” with phylon, meaning “race,” “tribe,” or “kind,” through the vocabulary of phylogeny. Its historical development reflects the increasing use of evolutionary trees and explicit criteria for judging the relationships among organisms. The related terms phylogeny, phyletic, and polyphyly share this Greek etymological foundation.
Related word forms
How monophyly is actually used
This is a technical term in evolutionary biology and cladistics. It is usually used in discussions of taxonomy, phylogeny, and the classification of organisms.
Easily confused with monophyly
Monophyletic means that a group includes a common ancestor and all its descendants, whereas polyphyletic describes a group that combines organisms from different evolutionary branches.