Digital PSAT Reading and Writing Practice Question 166: Answer and Explanation

Question: 166

A biologist attempts to determine the cause of evolutionary divergence among the populations of a frog found in the Amazonian rain forest. Based on her observations, the biologist supports the riverine barrier hypothesis, claiming that dispersion across opposite riverbanks is responsible for the observed differences in the frogs. She notes that the width, depth, and water speed of the rivers form an obstacle that makes it extremely challenging for the frogs to cross.

Which finding, if true, would most undermine the biologist's hypothesis?

• A. Discovery of increased industrial pollutants in one branch of the Amazon River system
• B. Presence of fish and snakes that prey on this species of frog in large portions of the river
• C. Observation of present-day mating of this frog by specimens from opposite riverbanks
• D. The popularity of tourist activities in the river system, including cruises and fishing expeditions

Correct Answer: C

Explanation:

(C) To undermine would be to show the flaws with an argument. If present-day frogs mate with one another from across riverbanks, this would hurt the notion that the river poses a barrier to frog mating. It is not (A), because the presence of pollutants in one branch of the Amazon would not determine whether cross-river mating could occur throughout the river system. It is not (B), because that would add support to the biologist's hypothesis, since predators in the river would present another barrier to the frogs' crossing the river. It is not (D), because tourist activity could also provide a barrier to frog crossing, supporting rather than undermining the hypothesis.