Question

peppered moths can have either a light wing color or a dark wing color. a scientist studied populations of both light and dark peppered moths over a 10 - year period. a graph of the data they collected is shown.
based on the graph, which is the best conclusion to make about changes in the moth populations by the end of the study period?
a disease has affected only the dark - winged peppered moth.
at present, wing color is not a factor in the success of peppered moths.
a new food source has become available only to the light - winged peppered moth.
at present, dark - winged peppered moths are being naturally selected for survival.

Explanation:

The graph shows the number of light - winged and dark - winged peppered moths captured over 10 years. As the years progress, the number of dark - winged moths decreases while the number of light - winged moths increases. This indicates that dark - winged moths are being selected against (not surviving as well), which is consistent with natural selection. Natural selection is the process by which organisms better adapted to their environment tend to survive and reproduce more successfully. In this case, if the environment (e.g., tree bark color due to pollution changes reversing) is favoring light - winged moths (they are better camouflaged), dark - winged moths would be less likely to survive (natural selection).

Answer:

At present, dark - winged peppered moths are being naturally selected for survival.