Determining whether or not something is natural requires that we can differentiate between traits that are the result of environmental factors and ones that are intrinsic to an organism's biology. In the broadest sense, traits include the physical and behavioral characteristics of an organism, but discussions about polyamory are typically centered on human behavior.
Early versions of the nature versus nurture debate argued that we're born with some degree of innate knowledge imparted by some unknown or supernatural means such as God, or conversely that innate knowledge doesn't exist and that we're born as a blank slate that is programmed by education and experience. Consider what the 16th century John Locke had to say:
Locke rejects the claim that there are speculative innate principles, practical innate moral principles, or that we have innate ideas of God, identity or impossibility. Locke rejects arguments from universal assent and attacks dispositional accounts of innate principles. - Stanford Encyclopedia of Philosophy
Since the late 1800s psychology has gained increasing academic respect and is now considered part of the social sciences. Consequently, behavior is now framed in a psychological context, and the mechanisms by which our psychology is shaped remain part of the debate.
With the discovery of genes, the idea that traits are intrinsic became linked to the study of genetics. Therefore God is no longer required to explain how innate knowledge and behavioral characteristics can be imparted.
So in recent times, the nature versus nurture debate tends to be one of genetics versus psychology rather than theology versus philosophy.TOP
Today there's little doubt that the majority of physical traits in living things are the result of an organism's genetic blueprint. There is also little doubt that physical traits heavily influence behavior. However the degree to which specific kinds of behavior is genetically blueprinted prior to birth or learned during life isn't always clear.
Over time, physical traits that facilitate behavior that increases the chances of survival and reproduction become a genetic predisposition for future generations. So on evolutionary time scales, the nature versus nurture question becomes a sort of causal paradox.
On top of that, learning and creation are also innate. In this context virtually all traits can be seen as either natural or learned or some combination thereof. So what justification do we have for saying that any sort of behavior, learned or otherwise, is more natural than another?TOP
Given the above, it can be argued that poly and mono relationships are both perfectly natural. However further reflection reveals that while this is superficially true, there is a qualitative difference. To reveal this difference lets have a closer look at the logic.
The rationale that one thing is as natural as the next distills down to the assumption that because it's perfectly natural for humans to learn and create, that the products of learning and creation are by extension also natural. That seems to make sense until we apply it to real life examples.
For example we can use the same argument to claim that synthetic food is as natural as organic. Clearly this example reveals that some things are more natural than others and that there are substantial qualitative differences between differing viewpoints.
But where does this leave us with respect to poly versus mono as ways of looking at relationships?TOP
As covered in the Introduction, the human capacity to experience romance evolved before the neocortex, making it a trait we've had for at least 3 million years. Therefore, regardless of cultural influences, romantic relationships between humans have been taking place as far back as recorded history, and even in cultures where romance between multiple partners has been repressed, humans have continued to do it anyway.
Similarly our perception of fairness is linked directly with our emotions, and psychological studies show that unfairness is experienced well before we learn about ethics on an intellectual level. In this context the word natural is more synonymous with organic in the sense that it's evolved rather than socially engineered. Therefore polyamorous relationships can and do happen whether anyone teaches us about polyamory or not, and have probably been happening for millennia.
According to evolutionary psychologist David M. Buss of the University of Texas at Austin, humans are in general innately inclined toward nonmonogamy. - Scientific American
Because polyamory recognizes our non-monogamous nature, the analogy to it being something organic is fitting. In contrast, relationships resulting from social conditioning can be fairly compared to being engineered, and there's little doubt that monogamous agreements, including marriages are engineered according to our social conditioning.
As with the difference between organic and engineered foods, there are consequences to consuming culture that conflicts with our nature. In western culture these side effects manifest in relationships as denial, which creates fertile ground for dishonesty, cheating, jealousy, and a host of related problems.
There is no exact number for the rate of our best estimates, which come from studies done in the last five to ten years, reveal that 45-50% of married women and 50-60% of married men engage in extramarital affairs at some point in their relationships. - Divorce MagazineTOP
Although monogamy and other marital relationships stemming from social conditioning can justifiably be compared to engineered foods, it's also true that we don't eat all our food raw off the ground while wandering around in bear skins and living in caves. Some engineering is good for us. The question is what sort of benefit does engineered monogamy have? Apparently it was good for the Romans. But why?
The ancient Greco-Roman and medieval European leaders who embraced anti-polygyny laws were heavily invested in the business of war, and their own social status and indeed survival often depended on their ability to maintain large, well-funded armies. And the imposition of monogamy produced bigger, better armies. - Psychology Today
It's hard to argue that the extensive influence that the ancient Romans have had on the development of Western civilization, or that Roman culture and conditioning was spread with the installation of Roman Christianity into Europe, which then migrated to North America in the 1600s.
But how relevant is that to modern society? Are large armies of shielded sword bearing soldiers fueled by religious mythology what modern relationships should be founded on? Most people probably don't give it much thought. However poly people often do consider the wider issues associated with relationships. For example, even if polyamory were the norm, some sort of social conditioning would still be required.
After all, education is valuable in helping to maintain community prosperity and stability. There are also practical limits to managing multiple relationships in large populations. So some form of governmental system would also be beneficial. But there's a different motivation at work between traditional mono relationships and modern poly ones.
Mono relationships are rooted in patriarchal rulership that serves a militant state and religious agenda, whereas poly relationships are rooted in gender equity and fairness as determined by the individuals in meaningful loving relationships. Which seems more in tune with human nature? Arguably humans are a bloodthirsty militant bunch, so perhaps there's a case to be made for either. But which do you prefer?TOP
Polyamory is part of our fundamental nature but conflicts with prevailing Western social conditioning. When mono people are faced with this conflict they are required to choose between embracing their natural selves or conforming to cultural norms. In many cases they give in to their natural instincts and that results in relationship breakdowns.
This problem can be solved by either consuming the engineered cultural diet we've been fed since childhood and enduring the consequences, or by embracing our poly nature and incorporating as many organic ingredients as are practical and beneficial.
Either way there are challenges and compromises. A poly relationship may be more organic, but acquiring organic ingredients is more hassle than going with what's readily available. How long are we prepared to go hungry before partaking in what's been put in front of us? A poly relationship may be fundamentally more natural, but keeping it stable with the addition of new partners also requires its own kind of engineering.
Ultimately it's up to each person in a relationship to decide what sort of combination of nature and nurture is going to make their relationship a recipe for success. Personally I like being my own person and being as organic as is practical, so I resonate well with a poly lifestyle, but also tend to be conservative in practice so as not to overcomplicate things or alienate me entirely from other possibilities.