Answer:
Natural Selection.
Step-by-step explanation:
Darwin observed the finches on Galapagos island where different, depending on the island they lived on and what food was available. A birds color can change or differ from other birds of the same species when their surroundings are different. For example a bird living in the jungle with many predators will adapt over time to a green color, while a bird from the same species living in a desert with no predators will not evolve or adapt to their surroundings since there is no competition.