The same species of squirrel lives on either side of the Grand Canyon. The squirrels on the west side of the canyon have adapted to have white fur, while the squirrels on the east side of the canyon have black fur. Which of the following has most likely led to the differences in fur adaptations? A. differences in squirrel reproductive rates
B. higher mutation rates on one side of the canyon
C. low genetic diversity in the initial population of squirrels
D. the isolation of the two groups in different environments