Whence marriage?

I went to the beautiful wedding of Catherine's friend in Birmingham this weekend, but I had been reading too much Brothers K and was in an overly analytical mood. When the minister described marriage and love as if both originated from and were the exclusive province of a Christian God, I found myself wondering about the institution of marriage. I was kind of surprised that I had read so little explaining how we got to the point where churches sanctified and appropriated what must have at one point been the spontaneous union of two people to form a family. I found some random articles and the Wikipedia entry but I'm still not satisfied. Still looking for something better. Maybe it's worth finding a book?