Finches are a type of bird that eat mostly nuts. Because of this, all finches have hard beaks. However, not every beak is the same. If a finch is born with an exceptionally hard beak, this can be a survival advantage. How is a harder beak an advantage?

AA harder beak will provide a reproductive advantage.

BA harder beak will allow the finch to fly faster and farther than before.

CA harder beak would allow the finch to use it to burrow even deeper into trees foraging for insects.

DA harder beak would allow the finch to crack open even the hardest shells, meaning it has a bigger food supply than most.