In every generation, more offspring are produced than can survive. There is a "struggle for existence." On the island the snakes don't have enough resources for all of them.
Hey why are you so small? Hey why are you that color?
The survival and reproduction of individuals is not random. The brown squirrels are more likely to survive considering they blend in more with the tree.
The other 3 are your fur
Well they have your eyes
There is a variation in this population. Horses are all apart of the same species but they produce fertile offspring, which means their offspring can reproduce to be many different colors or sizes.
Traits are heritable the puppies fur color resembles the fur color of their parents. The puppies also share very similar traits like how they look.