Don't add a hidden cost to a trait that's winning
- The idea
- Predict
- See it
- Why
- Check
The idea
“Every advantage has a catch, so a helpful trait will be held back by some cost.”
Biology is full of real trade-offs, so expecting a catch is a good instinct. Once you know who left more offspring, though, the catch has already been counted.
The short version
The mistake: Every advantage has a catch, so a helpful trait will be held back by some cost.
What's actually true: If carriers of a heritable trait leave more surviving offspring, the trait spreads, costs and all.
- Fitness is reproductive success, the number of surviving offspring an organism leaves compared with others in its population.
- Many traits do cost something, like energy or a higher risk of being eaten. Offspring counts are taken after those costs are paid, so the costs are already in them.
- When carriers of a heritable trait leave more offspring, the trait gets more common. Don't add a cost the question never gave you.
On the exam: Costs are already in the offspring count. Don't subtract them a second time.