Stabilizing selection

Definition

Stabilizing selection is a type of natural selection that favors intermediate phenotypes over extreme variations within a population. This process reduces variation and maintains the status quo for a particular trait, leading to populations becoming more adapted to their environment. It is essential in understanding how populations evolve, the genetic structure of populations, and the mechanisms driving adaptive evolution.

5 Must Know Facts For Your Next Test

1. Stabilizing selection often occurs in traits that are subject to high selective pressure, such as birth weight in humans, where both very low and very high weights can have negative effects on survival.
2. This type of selection can help maintain genetic diversity in other traits while keeping certain advantageous traits stable within a population.
3. Stabilizing selection contrasts with disruptive selection, where extreme phenotypes are favored and intermediate phenotypes are selected against.
4. The impact of stabilizing selection can be seen in many species, including plants and animals, where specific traits that enhance survival are consistently passed on.
5. It contributes to evolutionary stability by promoting traits that are already well-suited to an organism's environment, reducing the likelihood of drastic changes over time.

Review Questions

• How does stabilizing selection impact the genetic variation within a population?
  • Stabilizing selection reduces genetic variation by favoring individuals with intermediate phenotypes while selecting against extremes. This process leads to a decrease in the range of traits present in the population since those that do not fit the optimal range are less likely to survive and reproduce. As a result, over time, the population tends to stabilize around certain trait values that are best suited for survival in their environment.
• Compare stabilizing selection with disruptive selection and discuss their roles in adaptive evolution.
  • Stabilizing selection and disruptive selection represent two contrasting mechanisms of natural selection. While stabilizing selection favors intermediate traits and reduces variability, disruptive selection favors extreme traits at both ends of the spectrum. Both play significant roles in adaptive evolution: stabilizing selection helps maintain successful adaptations in stable environments, whereas disruptive selection can promote diversification by enabling a population to exploit different ecological niches or respond to changing environments.
• Evaluate the long-term effects of stabilizing selection on a population's adaptation and evolutionary trajectory.
  • The long-term effects of stabilizing selection on a population lead to decreased variability for specific traits, which can result in enhanced adaptation over time if those traits continue to match environmental demands. However, this reduction in diversity might make populations more vulnerable to environmental changes or diseases since they may lack the variation necessary for adaptation. In summary, while stabilizing selection can solidify beneficial traits, it also risks limiting a population's potential for future evolutionary changes as conditions shift.

Related terms

Natural Selection: The process where organisms better adapted to their environment tend to survive and produce more offspring, influencing evolutionary changes in a population.

Phenotype: The observable characteristics or traits of an organism, which result from the interaction of its genotype with the environment.

Genetic Drift: A mechanism of evolution that involves random changes in allele frequencies within a population, which can lead to reduced genetic variation over time.