Why do people beleive evolution?

i was sittin in science cl (at a christain school) and we were learnin about lyk the stomach and lyk the path of food and air and blood and all and recently we learned about the eye and there is just so many amazing things and i just wonder, what kind of person would beleive that all of this just "appeared" out of no where or that there was just a big BOOM and it was just all magically there... think about it