A trait that wins in one place can lose in another
- The idea
- Predict
- See it
- Why
- Check
The idea
“Some traits are just better, so a favored trait stays the fitter one wherever the organism lives.”
Fast, loud and big sound like good traits on their own. We call the winners well adapted and forget to ask where.
The short version
The mistake: Some traits are just better, so a favored trait stays the fitter one wherever the organism lives.
What's actually true: Whether a trait raises fitness depends on the environment. It can help in one place and hurt in another.
- Fitness is how well an individual survives and reproduces compared with others in its population. It's always measured in a particular environment.
- Selection favors heritable traits that help individuals leave more offspring where they live now. On lava or sand, the winner is the fur owls can't easily see.
- When the environment changes, selection can reverse. A favored trait can become a disadvantage, and its allele can grow rarer.
- Many traits carry a cost too. Bright colors help male guppies attract females but also predators, so bright males do best where predators are few.
On the exam: Fit always means fit somewhere. When the environment changes, the trait that's favored can flip.