Interpreting evolutionary trees

An evolutionary tree is a hypothesis about relationships based on evidence such as DNA sequences and shared derived traits. A branch point represents a common ancestor. Relatedness depends on the most recent shared ancestor, not how close names appear on the page. Rotating branches around a node does not change the relationships. Two species that share a more recent common ancestor are more closely related in that tree, even if their labels are drawn far apart. Branch lengths indicate time or change only when a scale defines them.