Brent Cornell

    
Selective breeding is a form of artificial selection, whereby man intervenes in the breeding of species to produce desired traits in offspring

• By breeding members of a species with a desired trait, the trait’s frequency becomes more common in successive generations
• Selective breeding provides evidence of evolution as targeted breeds can show significant variation in a (relatively) short period

Selective breeding of plant crops has allowed for the generation of new types of foods from the same ancestral plant source

• Plants of the genus Brassica have been bred to produce different foods by modifying plant sections through artificial selection
• This includes broccoli (modified flower buds), cabbage (modified leaf buds) and kale (modified leaves)

Selective breeding of domesticated animals has also resulted in the generation of diverse breeds of offspring

• Examples of selective breeding of domesticated animals can be seen in horse, cows and dogs

Example 1:  Horse Breeding

Horses have been selectively bred across many generations to produce variation according to a targeted function

• Race horses have been bred for speed and hence are typically leaner, lighter, taller and quicker
• Draft horses have been bred for power and endurance and hence are sturdier and stockier

Example 2:  Cow Breeding

Cows have been selectively bred across many generations to produce offspring with improved milk production

Farmers have also targeted the breeding a cows with a mutation resulting in increased muscle mass

• The resulting stock of cattle (termed Belgian Blue) have excessive bulk and produce more edible lean meat

Example 3:  Dog Breeding

Dog breeds show an enormous amount of variety due to the targeted selection of particular traits by man

• Hunting dogs (e.g. beagles) were typically bred to be smaller in stature so as to enter fox holes
• Herding dogs (e.g. sheep dogs) were bred for heightened intelligence in order to follow herding commands
• Racing dogs (e.g. greyhounds) were specifically bred to be sleek and fast 
• Toy dogs (e.g. chihuahuas) were selectively bred for their dimunitive size

Variation in Domesticated Dog Breeds