Directional Selection

Definition

Directional selection is a type of natural selection that favors individuals at one extreme of a phenotypic spectrum, leading to a shift in the population's trait distribution over time. This process results in the prevalence of certain traits that provide a survival or reproductive advantage, allowing those traits to become more common in the population. Directional selection is significant in illustrating how environmental pressures can shape species and contribute to evolutionary changes.

5 Must Know Facts For Your Next Test

1. Directional selection can occur in response to environmental changes, such as climate shifts, which may favor certain traits that improve survival in new conditions.
2. This type of selection can lead to rapid evolutionary changes, as seen in examples like the peppered moth during the Industrial Revolution, where darker coloration became advantageous due to pollution.
3. Directional selection is often measured by observing shifts in trait distributions over generations, indicating which phenotypes are favored.
4. It can also play a role in artificial selection, where humans breed individuals with desired traits, amplifying directional trends in domestic species.
5. The impact of directional selection can be seen across various organisms, influencing traits such as size, color, and behavior based on specific selective pressures.

Review Questions

• How does directional selection influence the genetic makeup of a population over time?
  • Directional selection influences the genetic makeup of a population by favoring individuals with traits at one extreme of the phenotypic range. Over time, this selective pressure leads to an increase in the frequency of those advantageous traits within the gene pool. As a result, the overall distribution of traits shifts towards the favored extreme, altering the population's characteristics and potentially enhancing their adaptability to changing environments.
• Compare and contrast directional selection with stabilizing and disruptive selection, highlighting their unique impacts on populations.
  • Directional selection favors one extreme phenotype, causing a shift in trait distribution towards that end. In contrast, stabilizing selection promotes average phenotypes by selecting against extremes, thereby reducing variation within a population. Disruptive selection takes the opposite approach by favoring both extremes and can lead to increased diversity and potentially speciation. Each type plays a unique role in shaping evolutionary outcomes based on environmental pressures and reproductive success.
• Evaluate the role of directional selection in contemporary evolution and provide examples of its effects on species adaptation.
  • Directional selection continues to play a significant role in contemporary evolution as species adapt to rapidly changing environments due to factors like climate change and habitat destruction. For instance, research on Darwin's finches shows how beak size has shifted in response to available food sources, demonstrating directional selection's influence on trait development. This ongoing process illustrates how specific selective pressures can drive evolutionary changes, ultimately affecting biodiversity and species survival in various ecosystems.

Related terms

Natural Selection: The process through which individuals with advantageous traits are more likely to survive and reproduce, leading to changes in the genetic makeup of a population over generations.

Stabilizing Selection: A form of natural selection that favors average individuals in a population, reducing variation by selecting against extremes.

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