What is selective breeding?

Weimaraner and French bulldog
Public Domain Karen Arnold

One of the earliest forms of biotechnology is responsible for many of the plants and animals that we know today.

Selective breeding, also known as artificial selection, is a process used by humans to develop new organisms with desirable characteristics. Breeders select two parents that have beneficial phenotypic traits to reproduce, yielding offspring with those desired traits. Selective breeding can be used to produce tastier fruits and vegetables, crops with greater resistance to pests, and larger animals that can be used for meat. The term “artificial selection” was coined by Charles Darwin in his famous work on evolution, On the Origin of Species, but the practice itself predates Darwin by thousands of years. As some of the earliest forms of biotechnology, both plant and animal breeding have been common practice since the birth of civilization.

Perhaps the earliest example of selective breeding is the domestic dog (Canis familiaris). It is unknown exactly when and where dogs were first domesticated, but humans have been breeding dogs for at least 14,000 years. Scientists believe that the domestic dog evolved from the wild gray wolf (Canis lupus), and through artificial selection, humans were able to create hundreds of different dog breeds. As people domesticated and bred dogs, they favored specific traits, like size or intelligence, for certain tasks, such as hunting, shepherding, or companionship. As a result, many dog breeds vastly differ in appearance, a unique phenomenon in the animal world, as different breeds of a single species generally resemble each other. The Chihuahua and the Dalmatian, for instance, are both dogs, yet they share few physical attributes.

Selective breeding has also been practiced in agriculture for thousands of years. Almost every fruit and vegetable eaten today is a product of artificial selection. Cabbage, broccoli, cauliflower, Brussels sprouts, and kale are all vegetables derived from the same plant, Brassica oleracea, also known as wild cabbage. By isolating wild cabbage plants with specific characteristics, farmers were able to create a variety of vegetables from a single source, each with differing flavors and textures. Broccoli, for example, was developed from wild cabbage plants that had suppressed flower development while kale was derived from Brassica oleracea with larger leaves.

Corn, or maize, is an unusual product of selective breeding. Unlike rice, wheat, and cabbage, which have clear ancestors, there is no wild plant that looks like corn. The earliest records of maize indicate that the plant was developed in southern Mexico 6,000-10,000 years ago from a grass called teosinte. Scientists believe that early Mexican farmers selected only the largest and tastiest kernels of teosinte for planting, rejecting punier kernels. This process allowed Mexicans to develop corn very quickly, as small changes in the plant's genetic makeup had dramatic effects on the grain's taste and size. Despite their physical dissimilarities, teosinte and corn only differ by about 5 genes. Today, corn is a staple in diets across the world. In 2012, an estimated 875 million tons of maize was produced around the world, primarily in the United States, China, and Brazil.

Evolution of corn from teosinteJohn Doebley/CC BY 3.0

Without selective breeding, many of the plants and animals on earth today would not exist. However, there are some disadvantages of artificial selection, especially in the case of inbreeding. Through inbreeding, two closely related organisms reproduce to yield a purebred with desired traits. However, these organisms may also have undesirable traits due to recessive genes found in both parents. Thus, purebred dogs are sometimes born with health defects like hip dysplasia and have shorter life spans than other mixed-breed dogs. Since artificial selection reduces variation in a population, breeders must be careful that their selectively bred organisms do not become too susceptible to diseases or to environmental changes.

Tags: Agriculture | Animals | Evolution | Farming

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