Which type of selection occurs when the environment is stable and there is no pressure for change?

• A. Stabilizing selection
• B. Directional selection
• C. Disruptive selection
• D. Natural selection

Answer: (A)

When the environment is stable and there’s no pressure to move toward an extreme, individuals with average traits tend to have the highest fitness. This pulls the population toward intermediate values and reduces extreme variations. That pattern is stabilizing selection: it favors the middle of the trait distribution because average trait values are best suited to the constant conditions, while individuals with extremes—too small or too large—tend to have lower survival or reproductive success.

A helpful example is infant birth weight in a stable population: babies with average birth weight usually have better survival chances than those who are unusually small or unusually large. That keeps the population’s trait values centered.

If the environment were changing, you’d see directional selection shift the average toward one extreme, and disruptive selection would favor the extremes over the middle. Natural selection is the broad process, but the specific pattern described here—stable conditions with a preference for the middle— is stabilizing selection.