A change in one lifetime isn't natural selection
- The idea
- Predict
- See it
- Why
- Check
The idea
“The trait shifted after the environment changed, so selection must have favored it.”
You probably pictured selection, since the average trait moved to fit the new environment. An average can also move because every individual adjusted.
The short version
The mistake: The trait shifted after the environment changed, so selection must have favored it.
What's actually true: If the same individuals changed, that's plasticity. Selection shifts traits across generations, by who survives and breeds.
- Phenotypic plasticity is one genotype making different phenotypes in different environments. Each individual changes during its own life.
- Selection changes a population over generations. Individuals with certain heritable traits survive and reproduce more. No individual's traits change.
- Clones that differ by environment point to plasticity. So does a shift where survival barely differed by trait.
- Selection can also shape plasticity, since the ability to respond can be inherited.
On the exam: Ask if the same individuals changed. If so, it's plasticity. Selection needs some to die or breed less.