That's rather a sweet outlook, if misguided, since we're related to all other animal life forms via evolution, so although some species that had developed into their present form before we did are still here, we all have the same forebears and started our evolutionary life journey at the same time.
I've had my present garden for six years and only recently discovered where the slugs live – underneath the leaf rosettes of Common Cat's Ear plants. I keep seeing hedgehog droppings so I guess the hedgehog(s), whose home(s) I haven't yet found, are eating well and keeping the slup population down. Frogs eat slugs too and we have some frogs, also rarely visible as there are so many places for them to hide.