How does being at the top of the food chain equate to civilization? Maggots are higher than us on the food chain, followed, I suppose, by birds that eat flies, followed, I suppose, by plants that are fertilized by bird droppings.
It equates to population growth as long as there is enough food. Unless there is war, pestilence, global flood, etc. Even then man tends towards population growth. 300,000 years of no growth, doesn't sound realistic.