Both of these appear in the early chapters of Genesis, and both are indicative of seminal moments in the history of man - events clearly moving men farther away from God in enmity against Him. This first one is about the line of Cain:
Polygamy entered the picture with Lamech, who was the seventh from Adam through Cain and was representative of a society that was quickly sinking in depravity and growing in contempt for God's way of life! His sons represented those people with material talents, but not with the right focus.
This example of moving away from the closest thing to a sanctified God plane marriage relationship is very significant!