It appears that there is an biological competition reason behind the word marriage. This biological mindset of envy would initiate some sort of sexual competition behavior as some requirement to Maslow's Hierarchy of Needs. Of course, marriage could be seen as some protective mechanism of social/sexual need. Of course, social than solidary animals would benefit with the assignment of some identity or function. However, social benefits are not insurance, are not guarantee. Exile can happen.

How does polyamory fit into this equation?

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polyamory has a different word root entirely in greek. poly amore. Poly means many, amore means to love the atmosphere given off by something. It means literally "a lover of the atmosphere given off by many things"

it's not a form of marriage nor a form of contract.

Polygamy is a different matter, it has Poly, meaning "Many", and Gamete meaning "Wife" in greek. It started as a counter for marriages and would have originally been treated as the two separate greek words kinda like you might say "I have a lot of apples" so it was a quantity descriptor or "counter", note it only is available in the form of multiple wives, if it was about women taking multiple husbands it'd be polygamys. but in ancient times for the described reasoning given in the description of marriage this was considered a deviant and shameful practice, some cultures even would not legally allow it (Rome in example) However in Rome Polygamy was normal.

lets clear this up, so Latin's word is polygamia however this is not pure latin, and was developed in later itallian times, it is not ancient latin. you can see from the word construction that this was a word adopted in Latin from Greek. So if polygamy was prevalent in ancient rome, how did they not have a word for it?

Simple, it was normal, it had been normal in all ancient cultures leading up to Rome. it was just considered +1 marriage. The word root starts with the offender: the Greeks. No doubt the greeks were emotionally sensitive and felt some prohibition about polygamy enough to create a term to reference it. That or it was a term devised as a form of braggary "I have Many wives" and such braggary may have developed the prohibitions about it due to the feeling of repulsion of listeners to the braggart.

Originally not a negative term, beta males of the time would have made it a shameful point of conversation.

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