Passage Summary: Scientists tracked two groups of the same bird species for 30 years. The birds in cages kept the same beak size, but the ones living in the wild ended up with much smaller beaks.

Reasoning: The researcher provides data showing that while captive birds maintained a consistent beak size over thirty years, the wild population of the same species experienced a significant decrease in beak size.

Analysis: To resolve this paradox, we need to identify an environmental factor that applied to the wild birds but not the captive ones. Since they are the same species, the change in the wild population is likely an evolutionary or adaptive response to a specific pressure, such as a change in food source or climate. The captive birds, living in a controlled environment with consistent food, would not face these same pressures. Look for an answer choice that introduces a specific change in the wild birds' environment that would favor smaller beaks.