In time Okham's razor reduced the many gods of polytheism to the one of monotheism. As knowledge advanced less phenomena needed an unknown outside force. A god concept doesn't pop into a child's head at a certain age, someone puts it there. There is no Evolution vs. Religion, and no Nature vs. Nurture. Religion would seem to be a survival mechanisn and it is our nature to be religions.
Nurture is simply the result of nature and environment.
Try to imagine what an alien sent from another world to observe and report back about what humans are like. Very little has been done to change for the better their existance, except to invent and make thinks to make their lives more comfortable but at the same time more complicated. They haven't yet learned to accept how they came to be, and thus are not ready to change the unnecessarily harmful and hurtful things about themselves, and conversely they are not able to fully enjoy. Tribal survival genetics has made them socially dependent in a cooperative yet controlling way with conflicts that leads to much unnecessay pain. Their beliefs help them cope and while momost of these beliefs are obviously contrived and passed on from generation to generation, they are a great source of comfort and make living more worthwhile.