Monophyletic or monophylogeny is a term used to describe a group of organisms classified in the same taxon that have one of the most common ancestors in recent times. A monophyletic group includes all descendants of this most common youngest ancestor. The word “monophylogeny” literally translates from Greek to “one-tribe origin”. A monophyletic taxon is also known as a “clade“.
By classifying organisms based on their biodiversity and evolutionary history, we can study how different organisms, past and present, relate to one another. In other words, this science of systematics helps us understand the evolutionary history of the world.
This system enables us to visualize the relationship of many organisms on a phylogenetic tree or cladogram, with branch order relationships and branch lengths indicating the extent of evolution.
Some scientists may use a broader definition of monophylogeny, which includes paraphyletic groups. A paraphyletic taxon is also defined as a group of organisms that share a most recent common ancestor. However, a paraphyletic taxon does not contain all of the descendants of this ancestor. Most scientists, however, will distinguish between monophyletic and paraphyletic groups.
Flexibility in Determining Monophyletic Relationships
This figure shows a cladogram of the order primates and examples for the classification of monophyletic, paraphyletic, and polyphyletic groups. According to this number, new world monkeys, old world monkeys, apes, and humans belong to the same monophyletic group since we all have a common ancestor of recent times. However, organisms can be classified differently depending on which common youngest ancestor they begin with.
For example, you can restrict the organisms belonging to a monophyletic group to old world monkeys, apes, and humans, when the ancient world ancestor most often considered is the ancient world monkey – or even to monkeys and humans, when the most common ancestor is considered in recent times is the monkey. Conversely, you can add tarsiers, lorises, and lemurs to a monophyletic group if the most common of the youngest ancestors is the lemur.