Natural Selection

Fitness
Stabilizing Selection
Directional Selection
Disruptive Selection
Speciation
Extinction

References:

Digital critters mimic behavior of real life

Natural Selection

Directional Selection

Directional selection favors those individuals who have extreme variations in traits within a population. A useful example can be found in the breeding of the greyhound dog. Early breeders were interested in dog with the greatest speed. They carefully selected from a group of hounds those who ran the fastest. From their offspring, the greyhound breeders again selected those dogs who ran the fastest. By continuing this selection for those dogs who ran faster than most of the hound dog population, they gradually produced a dog who could run up to 64km/h (40mph).

The greyhound was originally used to hunt the fastest of game, fox and deer. Their bred dates to Egypt in 3BC.