There is a population of animals that are called “Peppered Moths“. There are variations of them and some are, they mostly have white or gray wings and with dots on them. They actually sleep in the day and are awake in the night.
One of these traits are favorable because, for example if the moths wings are dark colored because it is easier for predators to get them.
The one trait that is not favorable is when the moth has really light colored wings because when an animal is trying to hunt for them, they will hide in trees and blend into them.
Overtime the unfavorable moth dies off because they since there is not enough of them, they can not reproduce more of their same trait.
The moths that have survived reproduce moths that also have dark colored wings.
After all of that the whole population is full of dark colored winged moths