Perhaps you're right. Perhaps you're just conjecturizing. Yes, we were animals. Now, we have the knowledge of good and evil, but if belief in God = fear of death, why so many martyrs? Because they have no fear of death, because they have something (Heaven/God/Reincarnation/etc) to believe. So, you see how your claim is circular? Even animals have a rudimentary fear of death otherwise they wouldn't fight back for survival, yet they genuinely lack a belief in God. They are "atheists" in the truest sense. I think there's something else involved with us that constitutes our belief in God besides the fear of death. Some call it "spirit." Now, it makes sense that those without the spirit (or rather, argue against the spirit, and as such argue against themselves) would rather us regress into animals while calling it progress (the saying "pissing in your face and calling it rain" comes to mind). This all starts with loosening human standards of behavior using a naturalistic fallacy. "Animals do it, therefore we should do it." Not every animal behavior is worth doing.