bifinches.jpgWhile visiting the Galapagos Islands, Darwin examined 13 different variants of finches. He proposed that the finches must have descended from birds that had flown to the island from the mainland. Because of their similar appearances, Darwin questioned whether or not they shared a common ancestor. However, he observed that the beaks of the finches were all slightly different, depending on their diets and habits. He suggested that this was caused by natural selection—due to food scarcity, some finches adapted slimmer beaks, which enabled them to eat other types of food. Through their DNA, they passed this genetic trait on to their descendants. This held the same for the giant tortoises on each of the islands. Darwin noticed that they differed in slight ways from island to island. This reinforced his theory of natural selection.