For which part?
In Africa, there have been many tribes that allow women to marry other women and use a man from outside the marriage to father children that the women raise together.
Now I know why I had never heard of it, the whole lets pretend that Sub-Sahara Africa has actually been culturally or scientificly significant to the world or that there where any "great civilizations" there that were the basis or foundation for future civilizations, movement didn't start until after I graduated high school.
There has been at least one recorded case of a family in China (centuries ago) who had a wedding for the dead daughter of one family with the dead son of another family so that the families could have a legal connection to each other.
Wow, one whole case to point to. Ok, accepted that it happened, but what about other cultures?
Sparta-- Boys entered the Agoge at around age 7. When they entered puberty, around age 12, they entered into a ritualized form sexual relationships with older students and instructors (yes, those students and instructors were also male), at 20, they joined fighting clubs (messes) and were again encouraged to have relations with other members. However, Sparta never recognized any of those relationships as marriage, at 30 they became full citizens and were allowed to marry so that they would produce an heir and sons for Sparta.
Japan--women were expected to produce male heirs in marriage. For royal families, at least, don't really know about the common people, a woman could be "divorced" for failure to produce a male child and the man could then choose another woman who could produce an heir.
Catholic teachings that governed Europe and European societies--Sex outside of Marriage was a sin and prohibited (not that people didn't do it, just that the Church and in some cases, the law since many, perhaps most laws came down from the Church, not just the local King,ets. said it was wrong) Sex was also not to be engaged in for pleasure, only for procreation. Failure to consumate was grounds for Anulment. Putting all three of these teachings together, Sex is for Procreation, sex is inescapably linked to Marriage.
Many, perhaps most Middle Eastern cultures did not recognise homosexual marriage, however, some (Ayatollah Khomeini reportedly being one) believed that your male friends were for pleasure, women were for making babies. Again, a longstanding and wellknown influential cultural that directly linked marriage to procreation. There are some Muslims today who try to discourage and even stop this longtime tradition about marriage and homosexuality. So that evidence would indicate that the practice was derived from pre-Muslim middle-eastern culture. I am not positive about the exact teachings of each, but this seems to be one of the big differences between Sunni and Shia (Shi'ite).
Marriage has been about family ties more than any other thing in history. Procreation is a secondary, like many other things such as business arrangements, ending family feuds, or joining countries/kingdoms.
Undoubtedly this has been true for the Aristocracy in many countries, but only to the Aristocracy and not the common people or common culture. Peasant farmers and other laborers really did not concern themself's with "Family ties", I am sure there are some exceptions, but then we are discussing the overall view, not a few exceptions.
What does all of this have to do with "modern" marriage, simple, the modern incarnation is evolved and handed down from previous generations. "Conservatives" in this case are conservative about changes and only adopt those changes slowly, "Liberals" are liberal about making changes. And why should we be concerned, simple, every previous "Democratic" culture, the ones we based ours on anyways, experienced "Moral Decay" and the break down of Marriage right before their fall. Does this "Moral Decay" and break down of marriage cause the collapse? That is a whole other topic for debate and there is a plethora of views on that subject, but, it cannot be denied that the decay and breakdown of marriage traditions did occurr, especially in Greece and the Roman Republic (Later, the Roman Empire after Julius Ceasar ceased power) Augustus Ceasar difinitly fought against that decay, he imprissoned his own daughter on a remote island for committing adultry.
So, other Democracies experienced "Moral Decay" and breakdown of traditional marriage just prior to their collapse, The US today started off as a Democracy and is currently seeing the same "Moral Decay" and breakdown of traditional marriage, not hard to see why many could conclude that America is about to fall unless we re-establish "Moral Decency" and traditional marriage. And this "Decay" is also coming at a time when we see our Economic strength declining, our military strength being stipped away and the country is mounting up indecent amounts of debt that we may never be able to repay without creating an unsustainable tax burden on our productive citizens. It would seem that that writing is on the wall and we are quickly heading towards collapse unless we change things.
5 states, Arizona, Illinois, Indiana, Utah, and Wisconsin, only allow first cousins to be legally married if they cannot procreate. Why let them marry at all if marriage is about procreation and they cannot be able to do so in order to legally marry?
Interesting, prior to this, I only knew of Mississippi allowing first cousins to marry, guess it is the only state that allows it and doesn't put a restriction on it.