Gen 1-2 (design of marrage; only two can be joined)
Gen 4:19ff (Lamach its inventor. Therefore how does the OT portray it?)
Dt 17:17 (Direct prohibition for king, therefore as example for people).
Divorce and remarriage as functional polygamy.
Polygamy as less damaging (in some respects) than other forms of adultery in that it keeps kids with their mom and dad more than divorce and remarriage.