Stabilizing selection

Definition

Stabilizing selection is a type of natural selection that favors intermediate phenotypes over extreme variations, promoting the stability of a population by reducing variation. This process helps maintain the status quo in traits that are advantageous for survival and reproduction, leading to a decrease in the extremes of a trait spectrum. In this way, stabilizing selection can enhance the overall fitness of a population, ensuring that successful traits are preserved through generations.

5 Must Know Facts For Your Next Test

1. Stabilizing selection reduces variation in traits by favoring average individuals, thereby increasing the frequency of intermediate phenotypes in the population.
2. This type of selection is commonly observed in traits that are critical for survival and reproduction, such as birth weight in humans, where extremes can be detrimental.
3. Stabilizing selection acts against both extremes of a trait, which means that individuals with extreme phenotypes are less likely to survive and reproduce.
4. This process can lead to a more uniform population over time, as traits that do not confer an advantage are gradually eliminated.
5. Stabilizing selection plays a crucial role in maintaining genetic diversity within populations by allowing some variation while promoting successful traits.

Review Questions

• How does stabilizing selection contribute to the maintenance of certain traits within a population?
  • Stabilizing selection contributes to the maintenance of certain traits by favoring individuals with intermediate phenotypes, which tend to have higher fitness than those with extreme traits. For example, in human birth weight, infants with average weights have better survival rates than those who are very small or very large. This selective pressure reduces the frequency of extreme traits over generations, promoting stability in those beneficial characteristics within the population.
• Discuss how stabilizing selection differs from other types of natural selection, such as directional and disruptive selection.
  • Stabilizing selection differs from directional and disruptive selection in its focus on intermediate phenotypes. While stabilizing selection favors average traits and reduces variation, directional selection shifts the trait distribution toward one extreme by favoring individuals at one end. On the other hand, disruptive selection favors extreme phenotypes at both ends of the spectrum while selecting against intermediates. These differences illustrate how each type of selection shapes population genetics and influences evolutionary paths.
• Evaluate the long-term effects of stabilizing selection on genetic diversity within a population and its potential impact on evolutionary adaptability.
  • The long-term effects of stabilizing selection on genetic diversity can lead to reduced variation as specific advantageous traits become more prevalent while extremes are diminished. Although this may initially enhance the fitness of a population by promoting successful traits, it can also limit adaptability in changing environments. A lack of genetic variation means that if conditions shift dramatically, the population may struggle to adapt due to fewer alternative phenotypes being available for natural selection to act upon, potentially risking their survival.

Related terms

natural selection:

A mechanism of evolution where individuals with favorable traits are more likely to survive and reproduce, leading to the prevalence of those traits in the population.

phenotype:

The observable physical or behavioral characteristics of an organism, which result from the interaction of its genotype with the environment.

genetic variation:

The diversity in gene frequencies within a population, which is essential for natural selection to act upon and can affect an organism's phenotype.