When a Lepidopterist Examined Museum Specimens of a Particular Moth

When a lepidopterist examined museum specimens of a particular moth species, she noticed that the variation in color was distributed as shown in the first graph. She was surprised because her data indicated the distribution of colors shown in the second graph. Which of the following hypotheses about the cause of this shift in the range of genetic variation is the most likely to be supported by examination of the distribution of colors in a collection assembled at a time between that of the collection of the museum specimens and her current specimens?

A) Darker moths tend to lay more eggs than light moths.
B) Birds prefer to eat lighter moths rather than darker moths.
C) The bark of the tree on which moths landed became darker over time.
D) Darker moths were more likely to survive and have more offspring over time.