I very highly dought Humans were created by Arceus. For one, Humans are the top species on the Pokeworld, and if my theory is correct, which I like to think they are, top species evolve into other top species. For example, Birds->Dinosaurs->Monkeys->Humans. Birds are claimed to be the first species that has ever existed, next to bugs. Then Birds evolved into Dinosaurs in order to survive in the rapidly changing world. Then somewhere before the extinction of dino's monkeys were produced as a mutation of Dinos. After the extinction, monkeys were (its arguable) the dominate species and they evolved into humans.
So therefore......there must have been another species of creature that co-existed with Pokemon before humans came around.