Evolution?ted

So I don't believe that things just happened by chance. it is all to complicated and beautiful for that but I do get scared when I realize that the human body is a machine and that plants and animals change "evolve" and adapt to their surroundings to survive. Like plants that adapt their selves to trap moisture because it is so dry. My fear is that if the plant can do the little changes on its own is there a possibility that it could do larger changes on its own? But there is no evidence for larger changes ever happening (from one species to another) so I wonder if the ability for minute changes is just one more program from a very large programmer of nature.