I believe. Seems like we make up reasons to ensure our survival as a race. Eg... Socially, if we can only survive in a group then we will create a society that makes us act as a group. Rules, like morals, beliefs, and so on back up the need.
And anyone who's had kids or worked in Social Services will know, we the people are basically out to get the best we can, and take the easiest route to it. By nature. Unless persuaded otherwise. I'm not being nasty here, I think it's true. A baby will find as much dominion as a parent will allow, thus ensuring food and nurture and life.
So, it used to be that we must marry and remain faithful to that partner to ensure the survival of the child... the new seed. And in my humble, and very non-conclusive opinion, our families no longer need to remain together because the child will live without it. And we no longer have to protect it with stories.
I think our myths and morals and social norms are borne out of the survival of the human race. Sounds basic, but viva la free choice. The bigger picture would push us back together if we couldn't get along alone.?????
Make sense? Feel free to rip it to shreds.