I was watching a Sam Harris lecture the other night. In the beginning of the lecture he makes an offhand statement that really stuck with me.
"The reality of death is absolutely central to religion. it's denial is central to religion. Without death, faith based religion would be unthinkable."
I dunno why, but that thought had never occurred to me before, but once you think about it, it seems to be completely true. What kind of religion would we have if we understood death and dying hundreds of thousands of years ago?
Faith based religion only makes sense in a world full of death, but to go farther, it only makes sense in a world full of ignorance and fear about death.
I'd say the same intelligence that evolved in human beings gave us a higher level of self awareness and the ability to contemplate our own inevitable deaths along with longer grieving sates of the deaths of our loved ones. Death anxiety followed and the trait of a predisposition to believe in gods, a soul and an afterlife became advantageous in abating the death anxiety and promoting the social order that would increase regional survivability for the humans.
Not unlike spoken language, which you can find in every culture, religion is also there. No matter how dramatically different they almost all share very common traits. But no one would argue that language isn't an innate construct of the mind. It's the same with religions. Even the religious will accept that as a fact....for other religions. It's only their own that is true and divinely inspired with a true supernatural diety that exists.