Stabilizing selection

Definition

Stabilizing selection is a type of natural selection that favors intermediate variants of a trait, reducing variation and maintaining the status quo in a population. This form of selection typically acts against extreme phenotypes, leading to a more homogenous population over time. It plays a critical role in preserving advantageous traits that are beneficial for survival and reproduction in a stable environment.

5 Must Know Facts For Your Next Test

1. Stabilizing selection reduces variance within a population by favoring average phenotypes and acting against extremes.
2. This type of selection can be observed in traits like human birth weight, where both low and high weights have higher mortality rates.
3. Stabilizing selection often occurs in stable environments where conditions remain relatively unchanged over time.
4. Examples of stabilizing selection can be found in plant traits, such as flower size, which may be favored at an intermediate size for optimal pollination.
5. Over many generations, stabilizing selection can lead to a more uniform population, as extreme variations are less likely to be passed on.

Review Questions

• How does stabilizing selection differ from directional and disruptive selection in terms of its effects on phenotypic variation within a population?
  • Stabilizing selection differs from directional and disruptive selection primarily in its focus on preserving intermediate phenotypes. While stabilizing selection reduces variation by favoring average traits, directional selection shifts the population towards one extreme phenotype, and disruptive selection promotes extremes at both ends of the spectrum. Each type of selection influences genetic diversity and adaptation differently, with stabilizing selection typically leading to decreased variability.
• Discuss how stabilizing selection might affect the evolutionary trajectory of a species over time, particularly in stable environments.
  • In stable environments, stabilizing selection can lead to a consistent evolutionary trajectory by promoting traits that enhance survival and reproductive success in those specific conditions. This results in the maintenance of certain advantageous characteristics while minimizing the potential for drastic changes. Over time, this can create populations that are highly adapted to their niche, but may also limit their ability to adapt quickly to sudden environmental changes.
• Evaluate the long-term implications of stabilizing selection on biodiversity and evolutionary potential within ecosystems.
  • Stabilizing selection can have complex long-term implications for biodiversity and evolutionary potential. While it helps maintain beneficial traits within a population, it can also limit the diversity of phenotypes available for adaptation in changing environments. If environmental conditions fluctuate significantly, populations that have undergone strong stabilizing selection may struggle to cope with new challenges due to reduced genetic variation. This could lead to increased vulnerability to extinction events or failure to exploit new ecological opportunities.

Related terms

Directional selection: A type of natural selection that favors one extreme phenotype over others, causing the allele frequency to shift in one direction.

Disruptive selection: A form of natural selection that favors extreme values of a trait at both ends of the spectrum, potentially leading to speciation.

Phenotype: The observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences.