Summary:
- Natural selection occurs when there are differences in fitness among members of a population.
- The example of sickle-cell anemia is described in the Figure below and Table below.
- It shows how natural selection can keep a harmful allele in a gene pool.
- Natural selection for polygenic traits is more complex, unless you just look at phenotypes.
- It may have a stabilizing, directional, or disruptive effect on the phenotypic distribution.
- It also shows that fitness may depend on the environment.