The first instance of polygyny was in the Bible, and concerned a man named Lamech.  Lamech was said to have taken two wives. His first wife was Ada, pronounced Aw’Daw.  The name means something like passed on or given to be put on.  Think jewelry that’s passed on to a daughter to be worn or passing by something and taking it for yourself.
The second wife’s name was Silla or Zilla pronounced Sillah’  and means something like shadow or shade.  I think the name was kind of saying that she was his comfort in the heat of the day.  So he had one wife that was his comfort, and one that he chose for her beauty.  So he sat down with them and said that he would protect himself (and them) from anyone who tried to hurt them.  That this verse talks about protecting someone from harm fits with the biblical narrative of this being just before the flood.

In the book, “Polygamy:  A very short introduction by Sarah M.S.  Pearsall, tells of a history of polygamy that is varied, interesting, and at times, horrifying.  Her research mirrors my own in many ways, but where I focus on Christians and Jews, she was far more broad in her research and I found it meticulous.