The average size of downy woodpeckers in North America gradually increases as one moves north.What term best describes this phenomenon?
A) Directional selection
B) Frequency-dependent selection
C) Muller's ratchet
D) Clinal variation
E) Genetic drift

Question

Quizplus · Accepted Answer

Clinal variation describes the gradual change in a trait along a geographic gradient. In this case, the gradual increase in downy woodpecker size as one moves north fits this description. The other options are unlikely to be at play in this scenario; directional selection implies that there is a selective pressure driving the evolution of larger downy woodpeckers, which is not mentioned in the question. Frequency-dependent selection refers to selection that depends on the relative abundance of different alleles in a population, and there is no indication that this is influencing downy woodpecker size. Muller's ratchet is a hypothesis that suggests that asexual populations will accumulate deleterious mutations over time, which does not seem relevant here. Genetic drift is a random process that can lead to the loss of genetic diversity in a population, but there is no mention of this in the question either.

The Average Size of Downy Woodpeckers in North America Gradually