Which form of natural selection favors extreme variations of a trait, shifting the population's average in one direction?

Which form of natural selection favors extreme variations of a trait, shifting the population's average in one direction?

• A. Directional Selection
• B. Stabilizing Selection
• C. Disruptive Selection
• D. Sexual Selection

Answer: (A)

This question is about how natural selection shifts the average value of a trait in a population when individuals with one extreme have higher fitness. When the environment or conditions favor one end of the trait spectrum, those individuals leave more offspring, so the population’s average value moves in that direction over generations. That shifting of the mean toward the favored extreme is the essence of directional selection. A familiar example is a color trait in moths during periods when environmental conditions favor darker forms, causing the population mean to become darker over time. Stabilizing selection, by contrast, favors intermediate values and tends to keep the average near the middle while reducing variation. Disruptive selection favors extremes at both ends, increasing variation and potentially creating distinct subgroups. Sexual selection focuses on traits that improve mating success and can produce exaggerations, but the mechanism described here—shifting the population mean due to differential survival or reproduction—maps onto directional selection.

This question is about how natural selection shifts the average value of a trait in a population when individuals with one extreme have higher fitness. When the environment or conditions favor one end of the trait spectrum, those individuals leave more offspring, so the population’s average value moves in that direction over generations. That shifting of the mean toward the favored extreme is the essence of directional selection. A familiar example is a color trait in moths during periods when environmental conditions favor darker forms, causing the population mean to become darker over time.

Stabilizing selection, by contrast, favors intermediate values and tends to keep the average near the middle while reducing variation. Disruptive selection favors extremes at both ends, increasing variation and potentially creating distinct subgroups. Sexual selection focuses on traits that improve mating success and can produce exaggerations, but the mechanism described here—shifting the population mean due to differential survival or reproduction—maps onto directional selection.