Amongst laymen, it is widely believed that Adam & Eve were monogamous? How did mankind arrive at this conclusion? Was it due to their religious upbringing or due to a general assumption that people in the “old days” were more moral or even prudish?
Let us explore the possibility.
Main picture: Adam & Eve in the quintessential fashion of the Stone Age Era or was this only one of the pieces that they displayed this day
What do we know about pre-agricultural man? Very little? Apart from a few stone tools, nothing remains of his language, religion, beliefs and way of life. Notwithstanding that we probably misidentify him as “stone age” based upon vestigial remnants. Perhaps he should rather be classified as “Wood Working Man” as they might have mastered the art of constructing elaborate wooden artefacts. Instead, we do not know because no wooden artefact would survive except under the most exceptional circumstances. Without any evidence to the contrary, Adam and Eve are classified as Stone Age.
Consider this. Stone Age Man roamed the earth in tiny bands with probably no affiliation to any other bands. Their only contact with other groups of humans would be chance encounters in an area where fruits and nuts were plentiful. Each group would have developed its own culture. By culture one is referring to the accepted norms and habits of a group of people. Nothing more and nothing less. Today there exists pejorative beliefs of other people’s cultures only due to the fact that it is perceived to be alien to one’s norms. Yet cultures are dynamic, in a constant state of flux.

Adam & Eve displaying their “his and hers” matching branches but with Eve in temptress mode plucking an erogenous apple
Consider the case of homosexuality. Until very recently, sexual acts by homosexuals were defined as sodomy and the offenders were sentenced to incarceration. In applying these norms and values, one of the most brilliant minds of the 20th century, AlanTuring, was sentenced to undergo chemical castration in the 1950s. Yet, if he had lived in the 21st century, he would no longer have had to show affection for or make love to another man without fear of arrest or ostracisation.

Cultural values are malleable
Furthermore, we have to ask ourselves why, if culture is so malleable, are aspersions cast or vindictive actions taken against those who violate “accepted” norms? Whose norms are they anyway? If they are so transient or fickle why does society place such great emphasis upon them?
Today the debate regarding the society in which Adam and Eve lived rages on. Based upon rather flimsy evidence, the debate between the “Ancient Commune” camp and the “Eternal Monogamy” schools of thought wends its tedious way.
Without adopting either postulation, I would like to refer to an earlier blog that I wrote about hippy communes. By rights, all should have espoused free love in an environment of heavy drug use. Yet some espoused monogamy, others licentious sex with others a combination of sexual mores with no drug use tolerated.

Hippie Commune
Without societal pressure except that of the commune itself, each adopted a different variant of “normal behaviour.” In effect, each had developed its own culture.
Similarly with the bands of Adam & Eve roaming on the open Savannah or the dusty plains of Mesopotamia.
Some bands would have espoused free love whereas in others, jealousies would have precluded any other behaviour than monogamy.

The treacherous Serpent beguiles an innocent Eve
Maybe the serpent did tempt Adam with the apple in the Garden of Eden, but was that an aberration?
No, it was just human nature.
Post script: The proof that there were multiple bands of Adam & Eves is obvious as all the paintings of this couple never display the same persons.
I’m thinking that a debate about the sex lives of fictional characters has a flaw at its core :-)