See Threesome Subtext for when this is hinted in canon, and One True Threesome for Shipping examples. May develop into a case of the Supporting Harem if one partner receives preferential treatment over the others.
For more details and some Real Life tidbits, visit Useful Notes On Polyamory.
Rather, it was most likely due to skyrocketing rates of chlamydia, syphilis, and gonorrhea from all the polygamous sex being had.
Within hunter-gatherer groups of 30 or fewer people, STI outbreaks would have a minimal effect on the larger population and be over relatively quickly, Tech Times reports.
But as humans took up farming and settled in larger groups, infertility-causing STIs would spread rapidly and hurt a group's ability to propagate itself, according to AFP.
"Open relationships are not nearly as socially accepted as they were in the 1960s and 1970s, at the peak of the sexual revolution.
But they do work for some couples, provided there's a tremendous amount of trust and commitment."Rather than requiring someone to pick one person out of several potential love interests, or have a Your Cheating Heart situation, all parties involved agree to be together and share cooperatively.
This typically lacks any drama of the decision itself, but has a different form of drama in how people make arrangements with each other, manage jealousy and households, and deal with the disapproval of society as a whole.
Individuals who identify as polyamorous may consider themselves "Ethical Sluts".
Not all ethical sluts are polyamorous, and not all people in polyamorous relationships have the "ethical slut" attitude.
The difference between a polyamorist and a swinger is that a polyamorous person has broad-spectrum involvement in their partners' lives, including love.
Swingers are largely there for the sex, often for the novelty of an unfamiliar partner. The Love Triangle or Love Dodecahedron can develop into this.
If it's just sex, not full-on relationships with more than two, it's Three-Way Sex. When a foreign or alien culture is particularly accepting of this, you may get Exotic Extended Marriage.