There are 3 types of natural selection: Stabilizing Selection-- The extremes are selected against. Example: height; mostly beings tend to the average height- not too many really short ones or really tall ones.

Directional selection-- One extreme value is selected for. Example: speed; faster is always better so a population will tend to get faster over time.

Disruptive selection-- The extremes are both selected for. This type of selection is not as common as the first two. Example: Prey-type animal with distinctive markings which the predators know will over time move away from the norm in both directions.