Well, seeing as Christianity DOESN'T hold the patent on marriage and in fact NEVER did......your religious beliefs or opinions really IRRELEVANT and rather boring to boot!!!
You really should take a read regarding Marriage throughout history especially in Western Civilization:
As Demosthenes, the orator, explained it: "We have prostitutes for our pleasure, concubines for our health, and wives to bear us lawful offspring."
Early in Roman history, a husband had considerable power over his wife and children, whom he could punish, sell, or even kill as he saw fit.
As we can learn from the Bible, the ancient Israelites had a patriarchal family structure. The status of women was low—they were regarded as the property of their fathers or husbands and could do nothing without their consent. The main purpose of marriage was procreation and the perpetuation of a man's name. Every healthy person was expected to marry. Single men and women were despised. A man could have several wives and concubines.(Jacob married two sisters, Leah and Rachel, and Solomon had 700 wives and 300 concubines.)
The Bible indicates that the marriage laws and customs of Israel changed somewhat in the course of time. Thus, divorces were increasingly frowned upon, and there was a general trend toward monogamy. Another change concerned the so-called levirate (i.e., the man's obligatory marriage to his brother's widow). This kind of marriage was at times required (Deuteronomy 25:5) and at other times prohibited (Leviticus 20:21). This change was probably related to changing economic conditions.
Yet still remained a MALE FEMALE formally recognized union. Sooooooooo.....despite all those changes over the past 600 years, the composition, male female, of the marital union, stayed the same.Interesting how marriage laws have changed over the last 600 years or so!!!