Question

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
disruptive selection
ecosystem selection
stabilizing selection

Explanation:

• Directional selection: Favors one extreme phenotype. Here, bear size shifts (large in cold, small in warm) in a direction based on environmental (temperature) change.
• Disruptive selection: Favors two or more extreme phenotypes over intermediate. Not the case here as it's a single - direction shift (size change with temperature).
• Ecosystem selection: Not a standard evolutionary selection term.
• Stabilizing selection: Favors intermediate phenotypes. Opposite of what's described (no favoring of'medium - sized' bears; size changes with temperature).

Answer:

A. directional selection