You can be born and not believe in scientific theories or God> Essentially, it IS possible to have no belief. And since the definition of atheism is "without a God," we were ALL atheists at one point. Is it to unreasonable to say that some of us only graduated a little farther along that line. And we don't necessarily "believe" in theories. We accept that some might be true, but they are subject to change, which causes us to change our thought process to suit the facts as we know them. If you refuse to accept change, than you truly do "believe" in theories.