Question

in 1988, evolutionary biologist richard lenski began the long - term evolution experiment (ltee) using twelve populations of escherichia coli. for over 30,000 generations, the bacteria subsisted on glucose, ignoring the abundant citrate in their environment, until one population suddenly evolved the ability to metabolize citrate. lenski hypothesized that this innovation required a specific sequence of earlier potentiating mutations that had no immediate benefit but set the stage for the final change. subsequent genomic analysis supported this view, confirming that the trait was historically contingent.
6
mark for review
which choice best describes the function of the underlined sentence in the text as a whole?
a it offers an explanation for how the metabolic change described in the previous sentence could have emerged.
b it summarizes the results of the genomic analysis described in the final sentence.
c it presents a hypothesis proposing the mechanism by which the theoretical evolutionary development described in the preceding sentence may have occurred.
d it proposes a causal mechanism to account for the surprising evolutionary innovation mentioned later in the text.

Explanation:

1. Analyze Option A: The underlined sentence is a hypothesis, not an explanation (explanations are supported by evidence, while this is a proposed idea before genomic analysis). So A is incorrect.
2. Analyze Option B: The underlined sentence is before the genomic analysis sentence, so it can't summarize the results of that analysis. B is incorrect.
3. Analyze Option C: The preceding sentence describes the evolutionary development (one population evolving to metabolize citrate). The underlined sentence is Lenski's hypothesis about the mechanism (specific sequence of potentiating mutations) by which that development may have occurred. This matches.
4. Analyze Option D: The "surprising evolutionary innovation" is in the previous sentence, not "later" in the text. So D's timing is wrong.

Answer:

C. It presents a hypothesis proposing the mechanism by which the theoretical evolutionary development described in the preceding sentence may have occurred.