Atheism has been [around] far longer than any sort of theism has, the idea of God is one that had to be invented by people.
Alternatively, it could be that some form of theism is inherent in the way humans have evolved.
The only true atheist I have met was a total sociopath of a man, completely oriented to narcisism.
I have also met a lot of people who describe themselves as atheists, but in each of these cases it seems that their definition of atheism involves negating the idea of Deity (where "Deity" is an inclusive term for belief in God, Gaia, Goddess, multiple gods, pantheistic spirits, etc). So Deity was, through its negation, very much a part of their world view. In each of these cases there seemed to be some sense of rightness that pretty much functioned as Deity no matter what the person chose to call it. That is, their "atheism" seemed to be of the "I am not a believer in God (but I have pantheistic belief, or believe I am myself sacred, etc).
That one true atheist, the sociopath, never stated a belief or disbelief. That was unimportant to him. The only thing that was important to him was enjoying himself as much as he possibly could without paying for his pleasure if he could possibly arrange for someone else to foot the bill. He was a thief of convenience, a great imposter, and a con artist. But he was rarely a burglar and never an armed robber-- I think those would have required too much work.