Haman behaviour often takes its roots to animals.
We are already seeing related forms of polyamory in human as polyandry and polygyny.
Nature and Biology prefer polyamory.
Only socially acquired learnings restrict it.
And the same socially acquired learnings pave ways for it.
We can find many couples who practice polyamory in a very slightly different manner..
They understand, allow/ connive the polyandry or polygyny of their spouse. Both members of the couple knows but not disclose openly.

Society terms it cheating however.

Lady T, the 'age bracket' observation is a good one.

Before I go there, though...

I'd like to clear up a potential misconception. Poly relationships don't (necessarily ) take the form of extended households featuring orgiastic group-gropes or serial bed-hopping or what-have-you.

Many PRs are made up of discrete and discreet pairings.

Pairings!?

Yep. There are often separate lives involved, completely self-contained. They just happen to share some emotional and/or physical assets.

This brings up the issue of time, but that's another entry altogether.

It would seem that this is a young person's bailiwick. Younger folks are more intellectually adventurous, have more energy, are more open-minded in many cases. And that's often where the fascination is born.

There are a surprising number of later-in-life PRs. In fact, it's more common among older, more affluent, educated and 'worldly' folks, I think. I've spoken with many more 30-, 40-, and 50-somethings about this than I have those younger.

There are many reasons for this. Some of those include experience in the 'relationship pool', maturity, self-knowledge and -confidence. There are as many reasons as there are adherents (well, ok - probably LOTS more reasons than there are participants )

Perfect explained. :))))