A clade is one whole branch of the tree
- The idea
- Predict
- See it
- Why
- Check
The idea
“Species that look alike or sit close together on a tree make a clade, even if I leave a relative out.”
Lizards, snakes and crocodiles look so alike that grouping them feels obvious. A clade is about ancestry, though, and the crocodile's closest living relative is the bird.
The short version
The mistake: Species that look alike or sit close together on a tree make a clade, even if I leave a relative out.
What's actually true: A clade is one ancestor and all of its descendants. You can cut it off the tree with a single snip.
- A clade, or monophyletic group, is one ancestor plus all of its descendants. On a tree, that's exactly what one snip lifts off.
- Reaching across a fork breaks a group too. Snakes and crocodiles alone would need extra snips, because their ancestor also gave rise to lizards and birds.
On the exam: Find the members' most recent common ancestor. If any tip above it is missing, it's not a clade.