42. Natural selection against extreme phenotype is termed as
    (1) Directional selection (2) Diversifying selection
    (3) Disruptive selection (4) Stabilizing selection

Introduction

Natural selection shapes the diversity of life by favoring traits that enhance survival and reproduction. While some forms of selection push populations toward new extremes or split them into distinct groups, stabilizing selection works differently: it preserves the status quo by selecting against individuals with extreme traits and favoring those with intermediate characteristics.

What Is Stabilizing Selection?

Stabilizing selection is a form of natural selection in which individuals with average or moderate phenotypes are more likely to survive and reproduce, while those with extreme traits (either too high or too low) are less fit and are gradually eliminated from the population. This process narrows the range of variation and keeps the population centered around an optimal mean trait value.

Key Features

• Eliminates Extremes: Individuals at both ends of the trait spectrum are selected against.

• Favors the Mean: The average phenotype is favored, leading to increased frequency of intermediate traits.

• Reduces Variation: Genetic diversity decreases as extreme phenotypes become rarer.

• Maintains Stability: The population remains well adapted to a stable environment.

Classic Examples

• Human Birth Weight: Babies born with very low or very high birth weights have higher mortality rates, while those with average weights have the best survival chances. Over generations, this leads to most babies being born within a healthy weight range.

• Clutch Size in Birds: Birds that lay too few or too many eggs have lower reproductive success than those laying an optimal number, so the average clutch size is maintained.

• Fur Color in Stable Environments: Animals whose coloration matches the environment are less likely to be preyed upon, while those with unusual colors are selected against, keeping the population color stable.

Stabilizing Selection vs. Other Types

Evolutionary Significance

Stabilizing selection is thought to be the most common form of natural selection in nature. It maintains well-adapted traits in populations living in stable environments and prevents drastic changes, ensuring long-term survival and evolutionary stability.

Conclusion

Stabilizing selection is the evolutionary force that acts against extreme phenotypes, preserving the average and maintaining the stability of populations. By consistently favoring intermediate traits, it helps ensure that species remain well adapted to their environments over time.

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Stabilizing selection demonstrates that, in evolution, sometimes the safest path is to stay close to the mean.