The fossil record shows that the average size of black bears was large during cold glacial periods and got smaller during warmer time periods. What is this an example of?

Directional selection occurs when environmental conditions favor one end of a trait range, shifting the population’s average. Here, colder glacial periods favored larger bears, while warmer periods were associated with smaller bears, so the average size changed over time. This is directional selection, not stabilizing selection, which favors intermediate traits.

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