Tree squirrels can have different fur colors.

Question

Squirrels live in forests where foxes also live. Foxes hunt squirrels for food. Squirrels that have fur the same color as the trees are harder for the foxes to see and catch.

Diagram titled Population Before containing 2 rows of squirrel icons. The first row is labeled Brown and contains 2 squirrel icons. The second row is labeled Gray and contains 11 squirrel icons.
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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.

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.

Answer 1

The change in the color of the trees in the squirrels’ environment can be inferred from the change in the population of squirrels over many generations. In the first diagram, there were 2 brown squirrels and 11 gray squirrels, indicating that the environment contained few squirrels that matched the tree coloration. However, in the second diagram, after many generations, there is a significant increase in black squirrels, with 10 black squirrels present, along with just 2 brown and 2 gray squirrels.

This suggests that the environment of the squirrels likely changed to include darker trees, which provided better camouflage for squirrels with darker fur. As a result, the black squirrels were less visible to foxes, making them less likely to be hunted and more likely to survive and reproduce. Over time, these black squirrels became more prevalent in the population, while the squirrel colors that were less suited for the new environment (brown and gray) decreased in number.

In summary, the trees likely became darker, which favored the survival of black squirrels, allowing them to thrive over many generations while the number of brown and gray squirrels decreased. This is an example of natural selection, where the traits that enhance survival and reproductive success become more common in the population over time.