Okay, you have to understand my thoughts behind the whole line system, a line does not necessarily mean that the Poke'mon before created the preceding Poke'mon, but it is in fact related to it, as a underling kind of way. Examples of this are Lugia and Manaphy, Lugia, didn't create Manaphy but was put below him in terms of hierarchy. But there are ones that are directly created by the before one, Dialga, Palkia, and Garitina, were created by Arceus. The humans are needed for a few of the legendary Poke'mon, and if you really think about it, aren't humans themselves legendary, so I put them in the same evolutionary stance as Mew, him being the first of all Poke'mon. I see the evolution of creatures taking three lines in the Pokemon world, first legendaries, come about when there is a need to fill. Second Poke'mon, givin' fantastic powers and can change form(evolve) to meet needs. Third and finally humans, they were givin intelligence enough to change the situation they are in instead of changing their physical body. Now I see all humans and Poke'mon evolving about the same time. Now as for Arceus, I see as a Poke'mon that created six Poke'mon, and left them to do what they will, not directly effecting any of what they created.