You'd think, however there seems to be a sentiment that Christianity and its traditions are timeless, and mankind has never known any other way.
Probably so, but it's hard to say, and it probably depends on how broadly somebody wants to define what "religious doctrine" is.
Setting aside Christianity and dealing broadly with religiosity (or any other doctrine/teaching), at minimum what's needed is some social order for which to apply the teaching to.
To espouse or teach a doctrine infers you need at least an espouser or teacher and a listener or student. Implying the need for the most basic, crude "society".
Point is, it's fairly obvious that social habits and practices would predate doctrines and teachings.
Even if you believe in the concept of a deity and the timelessness that would entail, it still wouldn't mean religious (teaching) predates human socialism. As you most certainly would need one (human socialism) before the other.
To the topic of this thread...it's been mentioned that marriage started as a tool for a man to own or possess a woman. While that may have some element of truth throughout history and even today in the practical life of some marriages, it's pretty clear the overwhelming objective was/is to perpetuate a bloodline (of the man) and partition people into families.
If it was mainly a tool to "possess" women...why have extravagant ceremonies, exchange oaths/vows, exchange tokens of commitment, etc.? You don't need all that...certainly not some mutual oath in order to take ownership of something or someone.
If it were a matter simply of some ownership you would expect to see a history of auctioning and/or currency exchange. The only remotely similar case is in some cultures where maybe head of cattle or goats are given to the family of the wife to be. But that's more out of some courtesy, respect, etc. than an exchange of some currency for the women.
Clearly the nature of marriage as a custom is not just a legal one but in many cultures it is a religious sacrament. That is the reality. In the same respect, a couple need not be religious to be able to marry...therein lies the rub IMO.
For same sex couples I don't get the need to claim marriage when at the same time many are seeking to "divorce" the concept from a religious custom as a means of attaining family rights. If it's merely about attaining family rights, etc., why not for purposes of expedience accept some equal alternative? (Just a question).