Moving through Genesis, thinking about marriage.
Events that are recorded in the Bible are sometimes exactly that.
A record of events. It’s a mistake to assume every event in the Bible is there as a stamp of approval, a recommendation, or a permission.
Genesis 4:19 has the very first mention of a man having more than one wife. This is one of those kinds of events… a record… not a permission or recommendation or approval by God.
Just a fact. But highly noteworthy.
As such, I’d guess it was the first occurrence. And a precedent that many followed. Interestingly I think the only other mention of this dude Lamech, is that he committed murder.