A survival edge only spreads if it's inherited
- The idea
- Predict
- See it
- Why
- Check
The idea
“If individuals with a trait survive or reproduce more, the population shifts toward that trait.”
The winners breed, so you'd expect their traits to show up in the next generation. That's true for genetic traits. Size from good food or luck isn't passed on.
The short version
The mistake: If individuals with a trait survive or reproduce more, the population shifts toward that trait.
What's actually true: A population shifts toward a favored trait only when the trait is heritable, so the winners pass on the alleles behind it.
- Natural selection causes evolution only if a trait varies, affects survival or reproduction, and is heritable, passed to offspring through alleles.
- Selection acts on phenotypes, but evolution is a change in allele frequencies. If the edge came all from the environment, survivors carry the same alleles as the rest.
- Most traits depend on genes and environment. The more of the variation that comes from genes, the more of the edge reaches the offspring.
On the exam: Before you predict a trait will spread, check that it's heritable. Environmental differences aren't passed on.