. The Clydesdale is a large breed of horse that was used for specific farming purposes, such as plowing and pulling wagons. The biggest and most muscular male horses were crossed with the biggest and most muscular females to produce the strongest offspring possible. This is an example of

artificial selection/selective breeding

Explanation:

The illustration is an example of artificial selection.

By definition, artificial selection is the deliberate perpetuation of some traits in living organisms simply because the traits are desirable. The organisms are selected because of the traits and allowed to breed either naturally or otherwise in order to ensure that these traits appear or are even consolidated in the offspring of the breeding.

The offspring from selective breeding are expected to combine the desirable traits of the two parents and thus, appear better than each of the parents.