Charles Darwin used the finches to provide evidence for natural selection. He realized that the finches have different beaks because they are adapted to eat different kinds of food. For example, a finch with a big beak is very good at cracking open nuts, and a finch with a long beak is very good at catching insects. Darwin was able to see that the finches had a common ancestor which is why they were so similar except for their beaks. Eventually, this led to the theory of evolution.