Make that "only theory." There is no other scientific model that rationally explains the data.
Oh my. Please explain to me how Evolutionary Theory is the "only" theory in your little world. Obviously you are incapable of explaining Complexity Theory, Chaos theory, and Intelligent Design Theory. Apparently you haven't even heard of them!
Go at ONCE and read Noble Prize Laurate Illya Prigogine's "Order Out of Chaos" and then come back and claim that NO OTHER THEORY explains the diversity of life on this planet.
Sheesh. Just because your fourth grade teacher told you that there was no other god besides Evolutionary Theory doesn't mean that the little luddite was correct.