What are the types of selection?

In evolutionary biology, selection refers to the process by which certain heritable traits become more or less common in a population over time due to differential reproductive success. There are several types of selection that act on populations, each leading to distinct evolutionary outcomes. The main types of selection include:

Natural Selection:

Directional Selection: This occurs when individuals with one extreme phenotype are favored over individuals with other phenotypes, leading to a shift in the frequency of the trait towards one direction. For example, in response to environmental changes, individuals with larger body size might be favored over smaller individuals.

Stabilizing Selection: Stabilizing selection occurs when individuals with intermediate phenotypes are favored over individuals with extreme phenotypes, leading to a reduction in the genetic variation for the trait. This type of selection tends to maintain the status quo of the trait within the population. An example is birth weight in humans, where very low or very high birth weights are associated with increased mortality.

Disruptive Selection: Disruptive selection occurs when individuals with extreme phenotypes are favored over individuals with intermediate phenotypes, leading to the divergence of the trait into two or more distinct forms. This can occur in heterogeneous environments where different phenotypes have advantages in different niches.

Sexual Selection:

Intersexual Selection (Mate Choice): This type of selection occurs when individuals of one sex (usually females) choose mates based on certain traits, such as coloration, ornamentation, or behavioral displays. Traits that enhance an individual's attractiveness to potential mates are favored, leading to the evolution of elaborate secondary sexual characteristics.

Intrasexual Selection (Male-Male Competition): Intrasexual selection occurs when individuals of one sex (usually males) compete with each other for access to mates. This competition may involve physical combat, displays of strength or dominance, or other behaviors that enhance an individual's ability to secure mating opportunities.

Artificial Selection:

Selective Breeding: Artificial selection occurs when humans intentionally breed organisms with specific traits to enhance those traits in subsequent generations. This process has been used extensively in agriculture, horticulture, and animal breeding to develop domesticated varieties or breeds with desired characteristics such as higher yield, disease resistance, or aesthetic appeal.

Kin Selection:

Kin selection occurs when individuals behave altruistically towards relatives, thereby increasing the reproductive success of genetic relatives and indirectly passing on their own genes. This type of selection favors behaviors that promote the survival and reproduction of relatives, even at the expense of individual fitness.

Group Selection:

Group selection proposes that traits promoting the survival or reproductive success of a group or population may be favored, even if they are detrimental to individual fitness. This idea suggests that traits promoting cooperation, altruism, or social cohesion may evolve through selection acting at the group level.