More change doesn't mean an older split
- The idea
- Predict
- See it
- Why
- Check
The idea
“The lineage that has changed the most must have branched off the longest ago.”
Birds look so different from other reptiles that they seem to have been on their own the longest.
The short version
The mistake: The lineage that has changed the most must have branched off the longest ago.
What's actually true: Two lineages from one split have had the same time to change, so shared derived traits must show the order of splits.
- Each branch point on a phylogenetic tree is one split. Both lineages leaving it are the same age, however much each changed.
- Lineages change at different rates. If one group member has extra DNA differences from an outgroup, a relative outside the group, that lineage simply changed faster.
- Branching order comes from shared derived traits, new features inherited from a common ancestor. Crocodiles and birds share some that lizards lack.
On the exam: Two lineages from one split are always the same age. Use shared derived traits to read the branching order.