The Origin of Religion

I've got a project to do for school, and I thought I'd get anon's input. The topic I've chosen is The Origin of Religion. Now, don't get the wrong idea, this doesn't mean I think all religion came from one source, I just haven't been able to come up with a better title. Basically, I'm going at this with a purely scientific standpoint, looking at the reasons religions are formed, how they evolve, and why they've lasted so long. I'll also include some of the first instances of religion and why were how they were.

So far, I have the most functions of religion as:
To help give moral support.
To keep a stable social structure.
To "motivate" people.

These are, of course, a bit simplistic, but I think I've come close. If anyone has objections, changes, or anything else regarding this project, I'd be very much obliged if you'd submit them in a civil manner.

Religions indoctrinate people so they can be controlled, but they are a double edged sword for a tyrant. The medieval church rivalled Kingdoms in wealth and influence, all the King's nobles were indoctrinated from birth to follow the church and in order to make the church more believable they had to espouse charity and virtues etc..

The Karl Marx quote "religion is the opiate of the masses" is too simplistic to describe the purpose of religion, there are 100s of other factors at play.