Breeders use artificial selection, as opposed to natural selection, terms first employed by Charles Darwin in his seminal work On the Origin of Species, to choose individuals to mate from. The purpose may vary according to whether the animals are used as working animals (such as cattle herding dogs or draft animals), livestock (cattle, sheep, honey bees), or pets (dogs, cats, etc).
Selective breeding may be carried out for a wide range of desirable traits, such as, but not limited to: productivity, disease and parasite resistance, longevity, size, ease of handling (gentleness for bees, tight udders on cows), or even aesthetic appearance (show dogs). For selective breeding to take place, the breeder must be able to isolate, select and monitor individuals to be used for the breeding program; that is, they must thwart nature, and stop individuals in the same species from mating randomly. They must also note and record the characteristics of all progeny produced by the planned matings. Any inferior animals must be culled from the breeding population. Care must be taken that breeding is not so single-minded for some desirable traits that other, inferior traits may also be propagated.
Among the techniques used in selective breeding are:
The extent to which the characteristics of a subgroup of animals in the same species are refined over time, and the extent to which they will reliably reproduce progeny with consistent replicable characteristics and conformation, helps to differentiate between a type, or landrace, of animals and a pure breed.