There were religiously-based forms of non-monogamy, ethical and otherwise, from the dawn of time to the present. Christopher Ryan and Cacilda Jethá present a mostly-scientific overview of this, and of the social evolution of monogamy in humans in their 2010 book Sex at Dawn (some of their claims have been disproven in the decade since the book’s release). Modern polyamory and modern polyamorous communities, as opposed to individually chosen group marriages that existed in mostly-hidden manners or religious groups with beliefs regarding plural marriage, have their basis in the 1960s and 1970s and the so-called Sexual Revolution.
Birth control pills becoming available made young people better able to experiment safely while dating, instead of marrying young because of early pregnancies; and it led to a dating culture where monogamy was not assumed before it was discussed, that has evolved into our modern “hook up culture.” The pill also allowed married people not just plan their families, but plan extramarital encounters with less worry. Many people have heard of swinging - of couples with “special understandings” with each other, or of “key parties” where people took each others’ wives home - in the 70s before the specter of HIV/AIDS created a sort of “Great Repression,” where average sexual norms swung back in a more strongly monogamous direction out of fear. You also may have heard of communes in the 60s and 70s that included open sexuality or group marriages.
While most experiments in communal living did nothing non-traditional sexually, and many of those that did leaned toward celibacy or limited sexuality in some way, the minority of communes that endorsed free-love or group marriage tend to be those that captured the public imagination and some are those that evolved into the modern understanding of ethical non-monogamy and polyamory.
The Sandstone and Kerista intentional communities, both in California, both founded in the very early 1970s, operated in a manner that would be identifiable to most modern polyamorists as similar to their own relationship philosophies. Kerista existed for 20 years, splitting up in 1991, and operated on a shared-parenting, shared-finances, chosen family model, with shifting consensual group romantic and sexual relationships between the adults (who numbered between 12 and 25 adults at different points over the two decade history of the community). These relationships included periods where all the adults were connected to one another in a group or network, or where there were several divisions, but all the adults were connected to some variety of group relationship. They collectively operated a business that sustained the community and worked as a group to raise children and meet the emotional needs of the adults. The Keristan vision included a belief that economic, family, and romantic interdependence in communities, rather than nuclear monogamous families, were the best way for the world to move forward, and that they had a duty to share this vision with the world. Several shorter-lived communities spun off of their vision and plans existed in the 1970s and early 1980s.
At the same time as these intentional communities came to exist, support groups and publications positively portraying polyamorous relationships began to crop up. Some of these were short-lived, and others lasted long enough to have an impact on the form of modern polyamory. One, inspired by Heinlein’s Stranger In a Strange Land, was Oberon Zell’s Church of All Worlds. A member of this group, Morning Glory Zell Ravenheart, would coin the word polyamory in print for the first time, rather than referring to these relationships as “group relationships” or “group marriages.” These groups and publications existed across the United States - Family Tree in Boston was one of the longer-running periodicals on the subject, and Family Synergy in Los Angeles was similar - and one, Polyfidelitous Educational Productions, rebranded as Loving More in the early 1990s and still publishes today. The language used around polyamorous relationships had not yet settled, but the concepts were becoming more understood and community-building had begun. People living outside these intentional communities, but in non-traditional, multi-person relationships, had ways available to them to see that they weren’t the only ones that lived this way, as groups and publications appeared in the late 1970s and through the 1980s.
The 1972 book Open Marriage by Nena and George O’Neill brought swinging culture into the light, and there were a plethora of studies done by social scientists in the late 70s on swinging culture and habits that got a good deal of publicity.
The HIV/AIDS crisis of the 1980s, and the realization that this was sexually transmitted, and that it was not a disease limited to gay men, caused an overall cultural shock and slide back into somewhat more Puritan social mores. A shift into “any sexual activity will give you a sexually transmitted disease so you shouldn’t have sex at all, much less with multiple people,” as the national discourse slowed growth of a movement toward acceptance of open relationships, and publicity of the same.
In 1997, when the term polyamory had not yet caught on as the popular term, but people were beginning to try to swing the pendulum back toward the possibility of open relationships being more acceptable, Dossie Easton and Janet Hardy (then writing under the nom de plume Catherine Liszt) released the first edition of The Ethical Slut. The original did not explicitly contain polyamory but reflects on many of the tenets of honesty in running multiple concurrent relationships, communication within relationships, and owning one’s own needs even when asking partners for help with them that are a cornerstone of polyamorous relationships. It is sometimes considered the first popular book on modern polyamory, and its later editions directly address polyamory in added sections. The third edition (published 2017) includes the subtitle “A Practical Guide to Polyamory, Open Relationships, and Other Freedoms in Sex and Love” as well as interviews with young polyamorists for modernizing context along with the twenty year old original text, written by women now in their 60s and 70s, who grew up in a very different environment. The Ethical Slut linked the open relationship movement to various sexual subcultures (notably the gay and lesbian communities and the BDSM community) in a way that affected the future intersections of those communities online.
The Internet made the biggest and fastest changes to create modern polyamory as we know it today. As with so many other niche interests, people found and were able to communicate with people who shared their interests (in this case, flavors of open relationship), at a speed never before imagined. The explosion of message boards, blog groups and forums allowed people to find connections - friendships, new relationship options, people to debate with and build discourse with - with people near and far, and to realize there were enough other polyamorous people nearby to make in person community possible. This internet discourse stabilized (though certainly not standardized - see how many variations there are of some terms in our glossary!) the words we use to describe ourselves and our relationships. Overlap with some of the online forums and in person meetings of those other marginalized identities that The Ethical Slut drew into open-relationship discourse created additional opportunities for community building, and shaped some of that debate around terms we use.
Crowdfunding published one of the most successful books on polyamory in the last decade, More Than Two by Eve Rickert and Franklin Veaux, and online payment methods and crowdfunding sites like Patreon, Ko-fi, Kickstarter, and GoFundMe have all been used to help create or expand blogs, books, podcasts, and video channels exploring polyamory. Most recently, “secret” and “private” Facebook groups have become a space for people to be known to their local polyamorous communities and share information, experiences, and local events, without either the relative anonymity of previous forums nor the public visibility of “following” or logged-in commenting on polyamorous items in a social network that may include work contacts or family members.
Mainstream television shows and news outlets have begun to cover polyamory, and not always in a tabloid manner. Despite this, polyamory is not a protected status or trait, people can lose their jobs for being polyamorous, and many people’s families are not understanding if they reveal that they’re living a life that involves multiple loves. While it feels like we are on the edge of a kind of sea change about this, I recognize that I live in a liberal, coastal area, and this is not the case everywhere in the country, no matter how many cable channels do bits on celebrities with open relationships, or how many articles with stock images of three feet under sheets as their lead image have been run. Humans may have been non-monogamous depending on circumstances since the dawn of time, but when you consider that polyamory as a specific variety of that has only had 50 years to make its cultural inroads, the progress towards the mainstream that has been made has been amazing.