Read the Nodes, Not the Neighbours

You'll learnto read a tree at its nodes — tips are species, nodes are ancestors.

A phylogenetic tree is not a picture of who stands next to whom — its claim about ancestry is stored entirely in the nodes, the points where two lineages last shared an ancestor. Branches pivot at every node like a hanging mobile, so watch a tree rotate, and then watch the ladder fall over. Twelve short steps; press Next for each one.

AP BIOLOGY · 12 STEPS · 6 QUICK CHECKS · NODES = COMMON ANCESTORS · BRANCHES ROTATE FREELY · NO TIP IS "MORE EVOLVED" · v5

cladogram · read at the nodes

Before you start

What you're looking at

A cladogram of eight living bears: tips at the right edge are species alive today, and each branch point is a common ancestor.

The question

Where on the figure is the tree's claim actually stored?

Step 1 / 12