The light colored rock pocket mice in New Mexico blend in with the sandy soil of the area, but on darker lava flow, the light color makes them stand out, making them easy prey for owls, hawks, and other visual predators. A gene mutation has produced a darker fur color that makes the some mice better able to survive predators in the lava environment. Over time, the darker colored mice became more common in the area of the lava flow. Why did dark colored rock pocket mice first appear in the population?