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 occurs when environmental changes favor one extreme phenotype over others, shifting the population's trait distribution in a specific direction. Here, colder periods favored larger bear size (better heat retention), while warmer periods favored smaller size, showing a directional shift in average size with changing conditions. Disruptive selection favors two extremes, stabilizing selection favors the average, and ecosystem selection is not a standard type of natural selection.

Answer:

directional selection