It's universally hetrosexual and outside of Africa it's restricted to one woman.
"Yet another reason that government should not be involved in such things"
You haven't given a reason. Govm't is involved to recognize and protect rights. If you don't want govm't involved, then don't ask them to get married. Tthose that wish to be called married will get the license and be officially recognized as such.
You are perfectly free to call and have any relationship you want with whatever sex, species, or thing you want, but no one and no arm of the govm't will recognize the relationship as a marriage. It is a rights violation to coerce others into conforming to, or accepting that as marriage.
Government wants a monopoly on the contract. I have no problems with governemnt upholding the contracts agreed upon by private individuals, but governemnent has no legitimate authority to set the terms of the contracts themselves.
You seem to have ignored my comments about universiality and human history, Furthermore, polygamy is legal in Saudi Arabi and other countries, which are outside of Africa.