A biologist conducting a long-term field study noticed there were two types of mice in a valley. One type of mouse had webbed toes, and one type of mouse lacked webbed toes. A dam was built in the valley turning the land into a wetland. As the years passed, all mice living in the valley were found to have webbed toes. No mice were found with non-webbed toes.
Which statement best explains the observed change in the mouse population?
a. The mice grew webbing to move more efficiently in the new environment.
b. Webbed-toed mice survived better and reproduced more than mice without webbed toes.
c. Webbed toes in mice are controlled by the environment.
d. The increased water levels in the valley increased the mutation rate in the mouse population.