Every million years in a species' existence it will suddenly mutate to its next highest evolutionary level, having collected another million years' worth of collective biological experience. This is how evolution works.
Fittest does not mean strongest, or smartest. It simply means an organism that fits best into its environment, which could mean anything from "smallest" or "squishiest" to "most poisonous" or "best able to live without water for weeks at a time." Plus, creatures don't always evolve in a way that we can explain as adaptations. Their evolutionary path may have more to do with random mutations, or traits that other members of their species find attractive.
A lot of people in many species don't believe in evolution. Usually this is because they exist in the timeline far enough after the last 'evolution' that they don't have any oral, historical or genetic memory of it, or because they are not adequately sentient enough to grasp these concepts. These creatures instead make up stories using whatever they can look at in their immediate vicinity, be it the sun, clouds, oceans, mountains, panthers, or burning pinecone.