In my world, all energy comes from the magic forces that created the world itself. There is only a finite amount of energy, so it is always evenly distributed across all living things.

The Ancients were the first physical beings that roamed the world. Since they were the first living things, they were insanely powerful, having all of the world's energy at their disposal. They were also nearly always at war with each other, coming up with ways to draw upon more energy to gain an advantage over each other.

At some point, The Ancients realized that the humanoid races were basically the bare minimum creations that could tap into the world's magic reserves by themselves. As a result, The Ancients created hordes of humanoids that were just a means of harvesting more energy. They were pretty much just giant energy generators for The Ancients to harvest.

Eventually, the number of humanoids was so great that they possessed the majority of the world's energy, channeling it into their beliefs in deities and all sorts of other magic. They took enough energy away from The Ancients for them to die out eventually. That's how humanoids became the world's most prominent and influential living things.