The diagram above shows a population of squirrels that lived in a forest. Scientists had previously only seen brown and gray squirrels in this forest; they had never seen squirrels of any other color.

Question

The diagram below shows how the population changed after many generations.

Diagram titled Population Many Generations Later containing 3 rows of squirrel icons. The first row is labeled Black and contains 10 squirrel icons. The second row is labeled Brown and contains 2 squirrel icons. The third row is labeled Gray and contains 2 squirrel icons.
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How did the color of the trees in the squirrels’ environment change? Explain what happened to the squirrels over many generations.

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Answer 1

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.