The bunny population lives in a brown environment and the bunnies each have different traits that will determine how they survive.
More dominate bunnies are born that can survive in the forest. The bunnies with the less favorable traits will have a harder time surviving and reproducing.
Struggle to Survive
Not all the bunnies will match with the forest. Some bunnies are white. All of the bunnies in the forest are trying to survive and reproduce.
The white bunnies stand out over the the brown bunnies, that blend in with the environment. This makes them more likely to be killed more often than the brown bunnies.
Because of the species adaptation in the forest, brown bunnies are less likely to be killed by the wolf. The white bunnies are more visible to the wolf's eye and will easily get killed.
Only the genetically dominant bunnies survive and get to reproduce. Because most of the bunnies being brown pass on their traits to their offspring, therefore the brown bunnies will survive and reproduce.