Stabilizing selection

Definition

Stabilizing selection is a type of natural selection that favors intermediate phenotypes and reduces variation within a population. This form of selection occurs when individuals with traits that are average or moderate have higher fitness compared to those with extreme traits, leading to a decrease in the population's diversity over time. It highlights how certain traits are optimized for a specific environment, maintaining a balance that promotes survival and reproductive success.

5 Must Know Facts For Your Next Test

1. Stabilizing selection is most commonly observed in traits that are crucial for survival and reproduction, such as birth weight in humans, where both low and high extremes have higher mortality rates.
2. This type of selection helps maintain the status quo in a population by reducing the frequency of extreme traits while keeping advantageous intermediate traits prevalent.
3. Stabilizing selection can be a powerful force in shaping species adaptations, ensuring that populations remain well-suited to their environments over generations.
4. Examples of stabilizing selection can be seen in various species, including plants that maintain moderate flower size for optimal pollination and fruiting.
5. It is a critical concept in understanding evolutionary processes, as it demonstrates how certain environmental pressures can lead to the preservation of specific phenotypes while curtailing diversity.

Review Questions

• How does stabilizing selection differ from directional and disruptive selection in terms of its impact on phenotypic variation?
  • Stabilizing selection differs from directional and disruptive selection by favoring intermediate phenotypes and reducing variation within a population. In contrast, directional selection pushes the population toward one extreme phenotype, leading to shifts in trait distributions, while disruptive selection promotes two or more extreme phenotypes at the expense of intermediate traits. These differences illustrate how varying environmental pressures can shape populations in distinct ways.
• Discuss an example of stabilizing selection and explain how it operates within a population to enhance survival.
  • An example of stabilizing selection can be observed in human birth weight, where infants born at an average weight have higher survival rates compared to those who are significantly underweight or overweight. This phenomenon occurs because average-sized infants are less likely to face complications during childbirth and have better chances of survival postnatally. As a result, this leads to a reduction in the prevalence of both low and high birth weights within the population over time.
• Evaluate the role of stabilizing selection in shaping the evolutionary trajectory of a species and its implications for biodiversity.
  • Stabilizing selection plays a crucial role in shaping the evolutionary trajectory of species by favoring traits that enhance survival and reproductive success under stable environmental conditions. While it promotes the preservation of advantageous intermediate traits, it can simultaneously reduce genetic diversity within a population. This loss of variation may limit the population's ability to adapt to changing environments, highlighting the balance between maintaining successful traits and fostering enough diversity for future adaptability.

Related terms

Natural Selection: The process through which individuals with advantageous traits are more likely to survive and reproduce, passing those traits to the next generation.

Directional Selection: A type of natural selection that favors one extreme phenotype over others, leading to a shift in the population's trait distribution.

Disruptive Selection: A form of natural selection that favors individuals at both extremes of the phenotypic range, potentially leading to speciation.