Fig. 1

Components of an evolutionary tree. Three components common to evolutionary trees include lines, internal nodes and terminal nodes. The lines represent lineages. Terminal nodes occur at the tips of the branches and represent taxa whose relationships are depicted in the tree. An internal node occurs at the point where lines bifurcate and represents the hypothetical most recent common ancestor of the taxa in that clade. The branching pattern in an evolutionary tree produces a nested hierarchy of clades (shaded triangles). The American alligator and song sparrow share a more recent common ancestor with each other (circled in orange) than either does with the monitor lizard (circled in red)