Selective Breeding

Selective Breeding Definition

Selective breeding, also known as artificial selection, is the process by which humans control the breeding of plants or animals in order to exhibit or eliminate a particular characteristic.

The procedure involves identifying certain desirable features and finding two members of a species that exhibit the particular feature. A series of matings or breedings is then performed between the individuals with favored features to produce offspring that exhibit the feature and that can be used for future matings. The desirable phenotypic traits are passed from parents to offspring via theirgenes.

Although selective breeding can increase the prevalence of desirable traits by increasing the frequency of favorable genes within the gene pool, undesirable traits, which can cause hereditary health problems, can also increase as a consequence of inbreeding.

The term ‘artificial selection’ was first coined by Charles Darwin in his book On the Origin of Species to describe how humans had mirrored the process of natural selection through selective breeding.

Examples of Selective Breeding

Dogs

All modern dogs have been selectively bred by humans over thousands of years. Dogs were first bred from a common ancestor of the gray wolf (Canis Lupus), which was domesticated by humans with whom it lived in close proximity. It is widely speculated that these animals were first domesticated by humans for hunting and protection, although modern dogs have been bred for a variety of reasons, such as companionship, performing particular tasks, entertainment, or for aesthetic purposes. Today there are over 400 breeds of dog, meaning they have the widest phenotyperange of any mammal.

The highly specific traits that are selectively bred in to dogs can come at a huge disadvantage to their health. Not only can the lack of genetic diversity within the gene pool lead to hereditary health problems, dogs that are bred with deliberately accentuated physical features can suffer from their unnatural physical form. For example, bulldogs and other ‘flat faced’ breeds can suffer from breathing problems, while large dogs commonly suffer from bone tumors due to their excessive body weight.

Plants and Livestock

Almost all of the food consumed by modern humans has been selectively bred over thousands of years. Around 10,000 years ago when humans began living in permanent or semi-permanent settlements, they started to cultivate their own crops and herd flocks of livestock for the first time. Humans originally selected fruits and vegetables for qualities such as large size and sweetness unconsciously; the seeds of plants with the desirable qualities would have been given the chance to germinate through human consumption and cultivated within their latrines (toilets). Over time, other favorable qualities, such as oil content, seedlessness and fleshy texture, were all altered, leaving many human-cultivated fruit and vegetables unrecognizable against their wild counterparts. The same process occurred with domesticated animals such as sheep (bred for thicker wool), chickens (considerably larger than their wild ancestors), and cattle (bred for more muscle mass or increased milk yield).

One of the oldest and most widely documented examples of selective breeding for food is the selection of tall growing (for easier harvesting), disease resistant wheat, which yields large amounts of grain. Historically, smaller crops were removed from fields, allowing bees and other pollinators to pollinate only the crops with the most human-favored characteristics. Today, the breeding of wheat is a more scientific process; individuals with specific genes are identified and bred to create plants that have improved nutritional content and more intense flavors, and require less fertilizer or pesticide applications.

Culling

Culling is a form of selective breeding. Rather than breeding two animals that display favorable traits, animals with undesirable traits (such as aggressive behavior) are removed from a population. Culling can be performed either by killing the individual or by spaying/neutering in order to prevent reproduction. The animals which are left in the population go on to reproduce, whilst genes controlling for the undesirable traits are removed from population.

Hunting

Selective breeding is not always beneficial to humans. Poachers, who hunt and kill rhinoceros and elephants for valuable rhino-horn and ivory, have in recent years caused unintentional selection for animals with smaller horns and tusks. As the males with the largest horns are the most desirable to hunters, the genes that control for size are being rapidly removed from the population. Additionally, a gene mutation which results in elephants with no tusks at all is increasing within populations. With population numbers greatly reduced due to hunting pressure, it is possible that elephant tusks could disappear entirely. This is an example of the effect that pressures of modern human populations have on wildlife.

Related Biology terms

  • Inbreeding – The process of breeding from closely related individuals.
  • Genes – A single unit of genetic information, which is stored within DNA.
  • Phenotypes – Observable characteristics of an individual, resulting from its genetic information or environment.

Test your knowledge

1. Why do humans selectively breed fruits?
A. To make them different colors
B. To make them taste sweet
C. To make them grow faster
D. All of the above

Answer to Question #1

2. When did humans begin to selectively breed livestock and crops?
A. 100 years ago
B. 30,000 years ago
C. 10,000 years ago
D. 3,000 years ago

Answer to Question #2

3. Why do health problems arise from selective breeding in dogs?
A. Animals are stressed from breeding
B. Lack of genetic diversity
C. Animals do not grow fur

Answer to Question #3

4. Which of the following is not a form of selective breeding?
A. Culling
B. Crossbreeding
C. Artificial Selection
D. Behavior manipulation

Answer to Question #4
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