Why is it that when Darwin visited the Galapagos Islands, he found many different species of finches living on the different islands there? How can you explain the difference in their beaks?

Different environments require different characteristics in organisms. after being geographically isolated, the finches on each island evolved differently based on their environment. on one island, where the main source of food is nuts, finches with strong nutcracker beaks survived because they had a higher fitness, and passed down those traits to their descendants, resulting in a species fit for that environment. on another island, where the main source of food was bugs who lived inside flowers, a needle-nosed beak was much more beneficial, so finches with those beaks were the ones to survive, and eventually evolved into a different species from those with nutcracker beaks.