Mechanisms of Evolution

Artificial and Sexual Selection

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Christian Bien Portrait_edited.jpg

Ben Whitten

Learning Objectives

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What are these types of selection?
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Artificial selection refers to how plants and animals can be deliberately bred in order to produce the most desirable traits. For example, certain pigs are chosen to breed with each other which results in some really buff pigs with a high yield of meat!


Sexual selection is a selection process that occurs between males or between females in a population for an inherited trait that assists in the copulation or winning of a mate.

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How does artificial selection work?
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As mentioned before, artificial selection (sometimes referred to as selective breeding) is the breeding of plants and animals to produce desirable traits. Organisms with the desired traits, including things such as but not limited to size, taste or appearance are mated or cross-pollinated with organisms with similar desired traits.


There are three mechanisms/processes in artificial selection.


  1. In-breeding: Breeding organisms that are more closely related than the average members of a given breed or strain; such as sire to daughter, mother to son or full-brothers to full-sisters

  2. Line-breeding: Breeding closely related organisms, using multiple pedigree crosses from a single exceptional animal/plant; systematic use of in-breeding

  3. Out-crossing: Breeding together unrelated plants or animals that are less related than the average members of a given breed or strain


Artificial selection results in changes in allele frequencies in gene pools over time. The breeding for particular traits results in changes in allele frequencies over generations, and therefore this is a mechanism for evolution. Specific allele frequencies will decrease, and variation will also decrease, as humans breed for specific desirable traits. Artificial breeding is also often applied to sheep and cattle, as well as fruits and vegetables.

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How does sexual selection work?
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Sexual selection is a process linked to mating behaviours in animals, where some individuals with certain characteristics are more able to attract a mate and pass on their genes to their offspring.


Sexual selection can produce a phenomenon called sexual dimorphism where males and females have different appearances or sizes such as the peacock. There is a theory that sexual selections helps females choose mates who have a higher level of fitness.

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