Mixing up directional, stabilizing and disruptive selection
- The idea
- Predict
- See it
- Why
- Check
The idea
“The biggest changes are at both ends, so it must be disruptive selection.”
Your eye goes to the rows that changed most. The clue is which way each one moved.
The short version
The mistake: The biggest changes are at both ends, so it must be disruptive selection.
What's actually true: Name it by which values became more common. One end means directional, the middle stabilizing, and both ends disruptive.
- When a trait is heritable, values that help individuals leave more offspring get more common.
- In directional selection, one end gains and the other loses, so the mean shifts.
- In stabilizing selection, both ends lose and variation narrows. In disruptive selection, the middle loses and one peak can split into two.
On the exam: Mark each class up or down. One end up is directional, middle up stabilizing, both ends up disruptive.