Types of natural selection

There are different types of natural selection: directional, stabilizing and disruptive selection. Each of these types selects for a different phenotype.

We can define natural selection as the process in which the individual best able to live in a given environment survives, reproduces and passes its characteristics on to its descendants . This process is an important mechanism of evolution , since this selection causes characteristics to be maintained and increases their frequency, and may even lead to the emergence of a new species.

Natural selection can occur in different ways, being classified into three types: directional, stabilizing or disruptive selection.

→ Directional selection

Directional selection is the type of natural selection in which an extreme phenotype is favored and has its frequency increased in the population. It is the type of selection that causes changes more quickly than the others, being the type most used in artificial selections.

An example of directional selection can be seen in salmon that live in the Pacific Northwest. They have shown a reduction in their size in recent years because of the increase in net fishing in the region. This type of fishing ends up selecting larger individuals, which made the smaller ones have an advantage over the others, since they were not captured. Over time, a reduction in the average size of these fish was observed.

→ Stabilizing selection

An example of stabilizing selection occurs in some African regions, where the presence of a recessive allele(s) is observed that determines sickle cell anemia , a relatively serious disease. Despite being severe, many people present the gene, however, in heterozygosity (Ss). The permanence of this gene is important because it confers protection against malaria , a disease common in certain African regions. In this case, therefore, natural selection favored the permanence of the gene in heterozygosity, decreasing the frequency of the gene in homozygosity (SS and ss)

→ Disruptive selection

Disruptive selection is one in which extremes are favored and intermediate organisms are eliminated. An example of this type of selection can be seen in some African finches that are adapted to eating seeds. They vary in size (large, medium and small), but intermediate forms are rarely observed. This is because there are seeds that vary in hardness. Larger finches can feed on hard seeds, and smaller finches feed on soft seeds.

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