Final distribution of stabilizing selection: what is the outcome?

Final distribution of stabilizing selection: what is the outcome?

• A. Variation is reduced because extreme phenotypes are favored
• B. Variation increases due to selection for extreme phenotypes
• C. Genetic variation remains completely unchanged
• D. Stabilizing selection reduces variation by favoring intermediate phenotypes

Answer: (D)

Stabilizing selection keeps traits near the average by preferring intermediate phenotypes and selecting against extremes. Because individuals with intermediate traits have higher fitness, the population reproduces more of these forms and extremes become rarer. Over time, this narrows the range of phenotypes for that trait, producing a tighter, unimodal distribution centered around the mean. The mean trait value stays about the same, but the variation around it decreases as extreme forms are disfavored. An example is infant birth weight, where babies who are too small or too large have lower survival, so the population shifts toward mid-range weights. Therefore, the outcome is a reduced variation by favoring intermediate phenotypes.

Stabilizing selection keeps traits near the average by preferring intermediate phenotypes and selecting against extremes. Because individuals with intermediate traits have higher fitness, the population reproduces more of these forms and extremes become rarer. Over time, this narrows the range of phenotypes for that trait, producing a tighter, unimodal distribution centered around the mean. The mean trait value stays about the same, but the variation around it decreases as extreme forms are disfavored. An example is infant birth weight, where babies who are too small or too large have lower survival, so the population shifts toward mid-range weights. Therefore, the outcome is a reduced variation by favoring intermediate phenotypes.