This picture shows the natural habitat of these two rats and the enviorment they are surrounded by. The two rats are a stone gray color and the other a light brown color.
The two different color rats have a common predator, the owl. The owl eats the brown rats since they can see them really easy which they wont have the chance to reproduce and have new generations of themselves.
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Overtime the black rats reproduce which allowed them to spread the dark fur mutation which then spread to the new generation then they reproduce and so.