MCAT Biology Question 175: Answer and Explanation
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Question: 175
10. As the climate became colder during the Ice Age, a particular species of mammal evolved a thicker layer of fur. What kind of selection occurred in this population?
- A. Stabilizing selection
- B. Directional selection
- C. Disruptive selection
- D. Speciation selection
Correct Answer: B
Explanation:
The situation described in the question stem is an example of directional selection. In directional selection, the phenotypic norm of a particular species shifts toward an extreme to adapt to a selective pressure, such as an increasingly colder environment. Only those individuals with a thicker layer of fur were able to survive during the Ice Age, thus shifting the phenotypic norm.