Fitness is counted in offspring that breed
- The idea
- Predict
- See it
- Why
- Check
The idea
“The fittest individual is the one that lives longest or is strongest and healthiest.”
"Survival of the fittest" sounds like a contest to stay alive. In biology, fitness is scored in offspring that grow up to breed.
The short version
The mistake: The fittest individual is the one that lives longest or is strongest and healthiest.
What's actually true: Fitness is the number of offspring that survive to reproduce. Long life and strength only count if they raise that number.
- Biologists also call fitness reproductive success. It's always compared within one population.
- Traits often trade off. Energy that goes into a big body or a long life isn't spent on young, so selection can favor a type that dies younger but breeds more.
- When one type leaves more offspring, its alleles grow more common each generation.
On the exam: Fitness counts offspring that survive to breed. Whoever leaves the most is fittest, however long they live.