You are studying leaf size in a natural population of plants. The second season is particularly dry, and the following year the average leaf size in the population is smaller than the year before. But the amount of overall variation is the same, and the population size hasn't changed. Also, you've done experiments that show that small leaves are better adapted to dry conditions than are large leaves. Which of the following has occurred?
A) stabilizing selection
B) directional selection
C) genetic drift
D) disruptive selection

Question

Quizplus · Accepted Answer

Directional selection has occurred because the average trait (leaf size) in the population shifted towards smaller leaves, which are better adapted to the new, drier conditions. This indicates that individuals with smaller leaves had a selective advantage, leading to a change in the average trait of the population without affecting the variation or population size.

You Are Studying Leaf Size in a Natural Population of Plants