7.9 Phylogeny

Trees of relationship

A phylogenetic tree (or cladogram) is a branching diagram showing the evolutionary relationships among species. Each branch point (node) represents a common ancestor. The more recently two species share a node, the more closely related they are.

How trees are built

Trees are built from shared derived characters — traits inherited from a recent common ancestor — and increasingly from molecular (DNA) data. An out-group (a distantly related species) is used as a reference point. Trees are hypotheses, revised as new data arrive.

Key terms

Phylogenetic tree

A branching diagram of evolutionary relationships among species.

Cladogram

A tree built from shared derived characters to show ancestry.

Common ancestor (node)

A branch point on a tree where lineages diverge from a shared ancestor.

Shared derived character

A trait from a recent common ancestor used to group species.

Out-group

A distantly related species used as a reference point in a cladogram.

Try an AP-style question

Which pair shares the most recent common ancestor?

1. C and D
2. B and C
3. A and B
4. A and D