A study by Charles and Mary Brown has documented a reduction in the wing length of cliff swallows that live near busy roadways; the study proposes that the need to avoid being hit by cars is the evolutionary driving force for the change.How would you evaluate this hypothesis if wing length had also shortened in cliff swallow populations that live in the desert Southwest where traffic is virtually nonexistent?
A) The hypothesis would still be valid. Natural selection is driven by local conditions; the two populations are probably evolving independently and they have coincidentally acquired the same characteristics.
B) The hypothesis would raise some doubts; perhaps aerial predators or another factor yet to be identified are creating the necessity for better flying skills in both populations.
C) The hypothesis would not be valid, because the probability of the same wing length mutation arising in geographically distinct populations is extremely low.
D) The hypothesis would not be valid; if the need to avoid vehicular collisions is driving natural selection, then no evolution should be occurring in the population that lives in the traffic-free environment.

Question

Quizplus · Accepted Answer

If wing length had also shortened in cliff swallow populations that live in the desert Southwest where traffic is virtually nonexistent, it would suggest that some other factor besides vehicular collisions is driving the evolution of shorter wings. This raises doubts about the hypothesis that the need to avoid cars is the driving force for the reduction in wing length, and suggests that further investigation is necessary to identify what that factor might be.

A Study by Charles and Mary Brown Has Documented a Reduction