The squirrel species, sand squirrels, lives on a brown, sandy area. The squirrels are getting killed by the vicious crows from above.
More dominant squirrels are born that can survive in the desert. There is not enough food nor space that they can live on. The squirrels with the worst traits are starting to get killed.
Not all of the squirrels match with the desert. Some squirrels are blue and red. All of the Squirrels in the desert are trying to stay alive and not get eaten by the vicious crows.
The blue and red squirrels stand out other than the brown, sandy desert. That makes them get killed more often, other than the brown squirrels they match their environment and are killed way less often.
Because of the species adaption on the desert, Brown squirrels are better at not getting killed by the vicious crows, there for there getting killed way less often.
Only the genetically dominant snails survive and get to reproduce. Because most of the squirrels being brown, they pass on their traits to their offspring, therefore a greater bunch of the squirrels survive much, much longer.