* Natural selection acts on existing traits: It doesn't create new ones. Instead, it favors individuals with traits that make them better suited to their environment.
* Variation provides the raw material: If all individuals in a population were identical, there would be no differences in traits for natural selection to act upon.
* Examples of variation: Differences in beak shape in finches, fur color in rabbits, or resistance to diseases in bacteria are all examples of variation that natural selection can act upon.
In summary: Natural selection requires pre-existing variation within a population to exert its influence and drive evolutionary change.
