Do you think that it's possible that Jenova is simply an organic lifeform similar to bacteria that had no will of its own?

I envisioned it something like this. Jenova and Sephiroth become intertwined in a way that allows Jenova to act as an extension of his will and his body, yet Sephiroth is like the brain, and they can't really exist without the other, but they're both necessary for the events in the game to happen —

It makes me wonder what Jenova was like before. Does the Ultimania state anything about the Jenova from the past? Did it really have a will of its own or was it like a bacterium? If it was like a bacterium, that would explain why it did not succeed in nearly destroying the world the first time.