Image Caption
For any speciation event on a phylogeny, the choice of which lineage goes to the right and which goes to the left is arbitrary. These phylogenies are equivalent.
Image use policy: For non-commercial, educational purposes, this image may be used with a Creative Commons CC BY-NC-SA 4.0 license. Please credit as follows: © University of California Museum of Paleontology, Understanding Evolution, www.understandingevolution.org
See where this image appears on the Understanding Evolution website »
This image is part of a series:

Phylogenies (1 of 3) Tree-like not ladder-like
Evolution produces a pattern of relationships A B C D among lineages that is tree-like, not ladder-like.
Phylogenies (2 of 3) Left to right
Just because we tend to read phylogenies from left to right, there is no correlation with level of "advancement."
Phylogenies (3 of 3) Order doesn’t matter
For any speciation event on a phylogeny, the choice of which lineage goes to the right and which goes to the left is arbitrary. These phylogenies are equivalent.
Understanding phylogenies (1 of 4)
Understanding a phylogeny is a lot like reading a family tree. The root of the tree represents the ancestral lineage, and the tips of the branches represent the descendents of…
Understanding phylogenies (2 of 4)
When a lineage splits (speciation), it is represented as branching on a phylogeny. When a speciation event occurs, a single ancestral lineage gives rise to two or more daughter lineages.
Understanding phylogenies (3 of 4)
Phylogenies trace patterns of shared ancestry between lineages. Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages.