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Artificial Selection

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Biology

One of the most significant steps in developing the human race was domesticating plants and animals for our benefit. Over time, methods have been developed to produce greater crop yields and animals with optimum traits. This process is called artificial selection. Over time, these useful traits dominate the population.

Artificial selection describes how humans choose organisms with desirable traits and selectively breed them to produce offspring with these desirable traits.

Artificial selection is also known as selective breeding.

Artificial selection differs from natural selection, which is the process that results in the survival and reproductive success of individuals or groups best suited to their environment without human intervention.

Charles Darwin coined the term artificial selection in his famous book “On the Origin of Species.” Darwin had used the artificial selection of birds to gather evidence to explain his theory of evolution. Darwin started to breed pigeons after studying finches on the Galapagos islands to prove his theory. He was able to show that he could increase the chances of desirable traits in pigeons to be passed on to their offspring. Darwin hypothesised that artificial selection and natural selection functioned the same way.

Like natural selection, artificial selection allows reproductive success to individuals with specific genetic characteristics to increase the frequency of desirable traits in the population. Natural selection works because desirable features give the greatest fitness and ability to survive. On the other hand, artificial selection works by selecting traits based on the breeder’s desires. Individuals with the desired trait are chosen to reproduce, and those without the trait are prevented from reproducing.

Fitness is an organism’s ability to survive and pass its genes on to future offspring. Organisms better adapted to their environment will have higher fitness than those not.

The process of artificial selection

Humans control artificial selection as we select what trait is deemed desirable. Outlined below is the general process of artificial selection:

  • Humans act as the selective pressure

  • Individuals with desirable phenotypes are selected to interbreed

  • Desirable alleles are passed onto some of their offspring

  • Offspring with the most desirable traits are chosen to interbreed

  • Individuals that display the desired phenotype to the most significant degree are selected for further breeding

  • This process is repeated over many generations

  • Alleles deemed desirable by the breeder increase in frequency, and the less desirable traits ultimately can completely disappear over time.

Phenotype: the observable characteristics of an organism.

Humans started selectively breeding organisms long before scientists understood how the genetics behind it worked. Despite this, individuals were often selected based on their phenotypes, so the genetics behind the breeding was not so much needed. Due to this lack of understanding, breeders can accidentally enhance genetically linked traits to the desirable trait, harming the organism’s health.

Advantages of artificial selection

Artificial selection brings about several advantages, especially to farmers and animal breeders. For example, desirable traits might be able to produce:

  • crops with a higher yield
  • crops with a shorter harvest time
  • crops with higher resistance to pests and diseases
  • reduce costs because farmers can identify crops or animals from their resources to be used
  • create new plant and animal varieties

Disadvantages of artificial selection

Despite the advantages of artificial selection, many individuals are still concerned about the practice due to the reasons outlined below.

Reduction of genetic diversity

Artificial selection reduces genetic diversity as only individuals with desirable traits reproduce. In other words, individuals share similar alleles and are genetically similar. Consequently, they will be vulnerable to the same selection pressures, such as disease, which could drive the species into becoming endangered or even extinct.

Additionally, the lack of genetic diversity often leads to the inheritance of adverse genetic conditions. These artificially selected individuals often suffer health conditions and reduced quality of life.

Knock-on effects on other species

If a species is produced that has beneficial traits over another species (for example, a drought-resistant plant), other species in the area could be outcompeted as they have not had their evolution accelerated at the same rate. In other words, surrounding species will have their resources taken from them.

Genetic mutations can still occur

Artificial breeding aims to transfer positive traits from offspring to parents, but poor traits also have the potential to be transferred because mutations are spontaneous.

Mutations are spontaneous changes in the DNA base sequence of genes.

Examples of artificial selection

Humans have been artificially selecting desirable individuals for decades on crops and animals. Let’s look at specific examples of species that have undergone this process.

Crops

Crop yield is increased and improved by breeding crop species with superior results. Artificial selection helps meet the needs of the expanding human population; some crops may also be bred for their nutritional content (e.g., wheat grains) and aesthetics.

Cattle

Cows with desirable features, such as fast growth rates and high milk yield, are selected to interbreed, as are their offspring. These traits are repeated over many generations. As bulls cannot be assessed for milk production, the performance of their female offspring is a marker of whether or not to use the bull in further breeding.

Researchers have found that the selection for high growth and milk yield in cattle is associated with decreased fertility and fitness, leading to lameness. Inbreeding depression is often a consequence of artificial selection, increasing the likelihood of inheriting abnormal health conditions.

Racehorses

Breeders discovered many years ago that racing horses generally have one of three phenotypes:

  • All-rounder

  • Good at long-distance racing

  • Good at sprinting

If a breeder wants to breed a horse for a long-distance event, they are likely to breed together the best endurance male and the best endurance female. They then allow the offspring to mature and select the best endurance horses to breed further or use for racing. Over several generations, more and more horses are produced that have greater endurance performance.

Differences between artificial selection and natural selection

Natural selectionArtificial selection
Organisms better adapted to their environment tend to survive and produce more offspring.The breeder selects organisms to produce desirable traits in successive generations.
NaturalMan-made process
Produces variationProduces organisms with desired traits and can decrease diversity
Slow processRapid process
Leads to evolutionDoes not lead to evolution
Only favourable traits are inherited over timeOnly selected traits are inherited over time
Table 1. The main differences between artificial selection and natural selection.

Artificial Selection - Key takeaways

  • Artificial selection describes how humans choose organisms with desirable traits and selectively breed them to produce offspring with these desirable traits.
  • Natural selection describes the process by which organisms with advantageous alleles have an increased chance of survival and reproductive success.
  • Charles Darwin coined artificial selection in his famous book “On the Origin of Species”.
  • There are both advantages and disadvantages to artificial selection. For example, although artificial selection can increase crop yield for farmers, the process also decreases genetic diversity.
  • Examples of artificial selection include crops, cattle and racing horses.

Artificial Selection

The process by which humans choose organisms with desirable traits and selectively breed them in order to produce offspring with these desirable traits. Over time, the desirable trait will dominate the population. 

  • Disease resistant crops
  • Cattle that produce a high yield of milk
  • Fast racing horses

  • Humans act as the selective pressure.

  • Individuals with desirable phenotypes are selected to interbreed.

  • Desirable alleles are passed onto some of their offspring.

  • Offspring with the most desirable traits are chosen to interbreed.

  • Individuals that display the desired phenotype to the greatest degree are selected for further breeding.

  • This process is repeated over many generations.

  • Alleles deemed desirable by the breeder increase in frequency and the less desirable traits ultimately  have potential to completely disappear over time. 

The common forms of artificial selection include breeding crops to increase crop yield and interbreeding cattle to increase productivity (milk yield and growth rate).

The advantages include a higher crop yield, new varieties of organisms can be created and crops can be selectively bred to be resistant to disease. 


Disadvantages include a reduction in genetic diversity, harmful knock-on effects on other species and genetic mutations can randomly occur.

Final Artificial Selection Quiz

Question

What is artificial selection?

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Answer

The process by which humans choose organisms with desirable traits and selectively breed them in order to produce offspring with these desirable traits and over time increase their population.

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Question

What is natural selection?

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Answer

A natural process that results in the survival and reproductive success of individuals or groups best suited to their environment.

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Question

Individuals that have the desired trait are _______ to reproduce and those that lack the trait are _______ from reproducing.


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Answer

 selected, prevented

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Question

What are 3 methods of selective breeding?

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Answer

Artificial selection, inbreeding, hybridisation.

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Question

What is inbreeding? 


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Answer

Inbreeding is when you mate closely related individuals.

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Question

Why may artificial selection be a threat to the survival of a species?

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Answer

If we think about the benefits of evolution, it ensures that species are able to adapt to a constantly changing environment. Artificial breeding of plants and animals for selected traits could result in threat to the species because, due to reduced genetic diversity, it can't adapt to the new environmental conditions.

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Question

How may artificial selection affect other plants and animals?

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Answer

If a species is produced that has beneficial traits over another species (for example a drought resistant plant), other species in the area could be outcompeted as they have not had their evolution accelerated at the same rate and their resources are taken from them.

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Question

How can crop yield be increased through artificial selection?


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Answer

The introduction of disease-resistant crops can greatly increase crop yield for farmers.

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Question

How can artificial selection be used in cattle breeding?

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Answer

Cows with desirable features such as fast growth rates and high milk yield are selected to interbreed, as are their offspring. This is repeated over many generations.

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Question

How are bulls used in breeding for high milk yield?

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Answer

As bulls cannot be assessed for milk production, the performance of their female offspring is used as a marker of whether or not to use the bull in further breeding.

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Question

What are the three phenotypes of race horses?


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Answer

  • All-rounder
  • Good at long distance racing
  • Good at sprinting

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Question

How is artificial selection used in race horses?

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Answer

If a breeder wants to breed a horse for a long distance event then they are likely two breed the best endurance male and the best endurance female and then breed them together. They allow the offspring to mature and select the best endurance horses to breed further or use for racing. Over several generations, more and more horses are produced that have a greater endurance.

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Question

Give three pros of artificial selection.


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Answer

Enhances desirable traits, creates a new variety of species, is relatively simple.

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Give two cons of artificial selection.

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Answer

There's more risk of disease, it takes a long time, genetic diversity is reduced, harmful traits can be selected and passed on to the offspring.

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Question

What is the potential for artificial selection?

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Answer

Artificial selection can be used to increase the production or resistance of crops and animals used for human consumption, reducing the costs of farming and increasing the amount of food available.

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