The color of the trees in the squirrels’ environment likely changed to a darker shade, possibly due to factors like increased levels of pollution, the introduction of different tree species, or natural environmental changes. As a result of the change in tree color, the darker-colored squirrels (black) had a survival advantage over the lighter-colored squirrels (brown and gray).
In many generations, natural selection favored the darker squirrels because they blended in better with their darker surroundings, making them less visible to predators. This increased their chances of survival and reproduction. Over time, the population shifted significantly toward the black squirrels, as evidenced by the population distribution shown in the diagram: out of the total 14 squirrels, 10 are black, while only 2 are brown and 2 are gray. This illustrates how environmental changes can influence the traits in a population through natural selection.