The theory was founded by a man named Darwin, who created it when he visited the Galapagos Islands off the west coast of South America. He saw many birds of the same species, yet they all had different sizes and shapes of beaks. He concluded that, through time, the birds had adapted to their environment, and had different beaks for certain types of eating.
      The reason that this is controversial, is that it conflicts with religious beliefs. Never in the bible does it mention evolution, or a time for it. People believe that because of these beliefs, it should not be taught in school.