clade

Within a cladogram, a branch that includes a single common ancestor and all of its descendants is called a clade.

A cladogram is an evolutionary tree that diagrams the ancestral relationships among organisms. In the past, cladograms were drawn based on similarities in phenotypes or physical traits among organisms. Today, similarities in DNA sequences among organisms can also be used to draw cladograms.

The organisms in each clade are characterized by shared, similar features that they do not share with any other organisms in the cladogram. For example, a mammalian clade would include all mammals. The oldest common ancestors within a clade are located close to the trunk of the evolutionary tree, whereas newly evolved species form the tree branches farthest from the tree trunk. Cladograms represent hypotheses about the evolution of organisms and are subject to revision when theories are disproved and additional data become available. Often, many hypothetical cladograms are drawn and compared to choose the most likely hypothesis.