Good point, I was actually thinking of that when I wrote my post. I don't know which of the antique philosophers were atheists, but wasn't Plato an atheist? Don't quote me on that, I am speaking purely from ignorance.
Anyway, yea, I would also wonder what their idea of creation was? Do you believe they had some inkling of evolution but just didn't have proof for it, and thus never mentioned it? If they didn't have proof for evolution, and they didn't have proof for creationism, then evolution would be a belief just as much as creationism would.
Trippy stuff here. Haha
Some Buddhists groups were atheists. Many today will argue that Buddha was an atheist. But our conversation made me wonder as you have, what they must have believed. I've create a thread in the Buddhism DIR asking Buddhists about it. Will be interesting to see what they say