Natural selection is the most important cause of evolutionary change. Darwin found three important factors which lead to his theory. On Darwin’s journey, One of the things he discovered was adaptation. He found this by observing Finches beaks. The finches that ate seeds had thick beaks, if they ate insects they had skinny and pointy beaks, and if they ate cactus fruit their beaks sharp. The shapes and sizes made it easier to eat or hunt the food. Another thing Darwin discovered was variation. He observed barnacles and noticed that their body parts varied depending on the environment they were in. Finally, the last factor is artificial selection. After Darwin’s trip to the Islands, he turned to breeding birds at home in order to prove his ideas.