Natural Selection

Fitness
Stabilizing Selection
Directional Selection
Disruptive Selection
Speciation
Extinction

References:

Digital critters mimic behavior of real life

Natural Selection

Disruptive Selection

Disruptive selection, like directional selection, favors the extremes traits in a population. Disruptive selection differs in that sudden changes in the environment creates a sudden forces favoring that extreme. Think about the changes in the environment when that meteor crashed into Earth 65mya. A sudden decrease in light levels as the dust rose over large portions of the Earth. Extremely large tidal waves washing miles over the land. Increased seismic activity. The sudden lost of food along the coast, possible plague due to the high initial death rate, dust filling the lungs of animals would have been the most stressful on larger animals. Large animals need a large oxygen supply to supply energy to their muscles. They also need a large, constant supply of food. The the sudden drop of oxygen due the the dust, and the drop in fresh food, large animals would be stressed. If a plague started by the high death rate also hit these stressed animals, they would have been sorely pushed to survive. Evidence shows that they did not. So disruptive selection occurs quickly, selecting for those extreme traits that help organisms survive in the new environmental conditions.