A population of voles (very small mammals) live in a shady forest. The all of the voles are a light tan color, a dark brown coloration arises by a new mutation. The darker voles are harder for predators to see in the leaf litter, thus they are less susceptible to predation. After 10 generations the majority of voles in the population are the dark brown color. In the figure above the solid red line represents the number of light colored individuals before the mutation and the black dashed line represents the number of dark brown individuals after 10 generations. What type of natural selection are the population of voles going through?