According to the Vatican (http://www.vatican.va/roman_curia/congregations/cclergy/docu...): "Convincing testimonies to the normative nature of clerical continence in the fourth century can be found in individual Western patristic authors (such as Ambrose, Augustine, Jerome). The first known example of actual legislation is c. 33 of the Spanish Council of Elvira, the usual date of which is given as ca. 305"

it also goes on to say:

"As with other juridical institutions of the Church, with time clerical continence developed sharper and more defined outlines. From the fifth to the seventh centuries much provincial conciliar activity is seen in the West where both the obligation to continence is reaffirmed (indicating infringement), and greater precision, taking into account changed circumstances, is given to the law. Canonical collections would circulate and consciousness of legislating in conformity with a wider legal patrimony and with ancient tradition is sometimes made explicit."

I'm sure whatever the exact origin, it's motivation and rationale has probably changed with times. The Vatican site points out that Pope Hormisdas (5 14-23), was married, and that his son, Pope Silverius, succeeded him. But, Popes have done all kinds things that go against our current idea of the Catholic tradition, like executions: http://en.wikipedia.org/wiki/List_of_people_executed_by_the_....

I've found the Vatican website is a pretty fantastic resource for information, and that Vatican scholars don't necessarily toe a specific line.

I'm not a religious person. It was something that really worried me as a kid growing up Catholic. I used to be afraid that God would be mad because I didn't believe in him enough. So, my personally point of view doesn't matter too much here, I suppose. But here it is anyway:

I don't think that we've got this existence situation figured out. For me, the more I looked at religions, the more I kept finding a human face behind every edict or ceremony that was associated with it. It's not so much that I don't believe in God, but I don't believe that we have anything on our hands that can address that question. In mass, the priest would hold up a King James Bible and say "This is the word of the Lord". Well, it doesn't take much research to see how the Bible was edited over time. So, yes, maybe God's hand guided that editing, but maybe not. And maybe it's not literal, and some sort of device for faith-based interpretation, but then maybe the Koran is too? Maybe a mountain or a lake is? At any rate, I want to do good in this world, and I try to. IMHO, nobody has it figured out.

Allowing priests to marry might reduce the amount of pedophilia in the Church. So yes, I think that's a powerful argument for it. Especially when the practice has such murky origins.