Isn't evolution just mutation?

Yes, you have the fossil records and all of that stuff, but it's not like any animal thought: "I need to grow more fur." Of course, they didn't think at all, they just have instinct. It just so happened that a mutant animal was born. And the mutant that had this trait, survived in that environment, while other animals died off. So why not call shorten it to the theory of mutation? Then, it wouldn't really be a theory, and would be much more plausible.