Pick the history with the fewest changes
- The idea
- Predict
- See it
- Why
- Check
The idea
“Any history that ends with the right species having the trait is as good as another.”
Many histories end with the right species holding the trait, so they all seem fine. They differ in how many events they assume.
The short version
The mistake: Any history that ends with the right species having the trait is as good as another.
What's actually true: When several histories fit the same data, the one that needs the fewest gains and losses is best supported.
- Each gain or loss of a trait along a branch counts as one change.
- Biologists favor the history with the fewest changes. This is called parsimony. Each extra change is one more event to assume.
- Separate gains do happen. Bird and bat wings evolved separately, and many other traits show those groups are far apart.
On the exam: Count the gains and losses each history needs. Fewest wins.