Artificial Selection

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.

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.

Fig. 1 - The process of artificial selection

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.

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.

Fig. 2 - Cattle that has been selectively bred for its high growth rate

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