The deer mouse in sand hills of Nebraska are ___________ in color.

The correct answer is: Light brown

 

The reason seems obvious enough: Mice that have dark fur and live on light sand are easy pickings for hungry hawks and owls. A genetic mutation led to lighter fur, and the sandhills mice lucky enough to be born mutants were more likely to survive and breed. With each generation, the population of light mice would grow, while that of the dark mice would shrink, until eventually, the bulk of the sandhills mice sported lovely beige fur.