Today, we still have a variety of gods and their central points of popularity follow governmental and cultural borders. If you are born in the US, you are likely Christian--this probability goes up further in the south, among conservatives, among whites of a European background, ect. Likewise, if you are born in India you're likely Hindu. Just like the historical examples of the past, the values of the gods believed fall in line with the cultures in which they were created. It's also true that, in the case of long-standing faiths, the morality attributed to a particular god and therefore as the standard to be followed shifts as it is adopted by new cultures or as the culture progresses. A possible reason for this is congregation retention. If a value goes out of favor that is a staple of the religion, the religion must adjust it's staples or lose their members to competing religions that have that more popular value. Or, as we atheists prefer, they defect from faith-based worldviews entirely and start a secular life.
The adoption to something like Christianity can be traced from the conversion of social/political leader to social/political leader who, in turn, either forces or encourages the adoption of the faith among his followers. Religions tend to ramp up in popularity when the leaders gain more territory and influence.
All this shows that the idea of Yahweh/Jehovah/Christ/whoever is not spontaneous, but the product of systematic indoctrination from culture to parent to child. The genesis of the idea of the god is harder to nail down because it goes so far back, but the imagination and creativity of humanity is well documented. We have covered every story I can imagine. (Admittedly, this is why I'm not a novelist.) What else is well documented is that charismatic individuals can convince a following so completely that they are willing to kill or be killed over ideology. Religious faith is more often than not the drive for this absolute compliance--just Google "cults" or "suicide bombers." I'm not equating Christianity in general terms to the harm caused by most of these groups, but think of how easy it would be to convince someone to believe some strange things, donate a little money and go to church Sundays compared to convincing people to take their own life. Jesus, Mohammad, and Joseph Smith are possible examples of these charismatic people.
The religions of this or that time of conception also take into account the scientific knowledge of the day as a base to start filling in gaps with faith alone. More modern religions deny or contradict less of what we (at least most of us :-) now understand. That could be another whole rant, and I've probably typed enough for now.
