Monogamy—one partner for one person—is a cultural practice we take for granted. It seems as natural as breathing: Two partners commit to each other, stay faithful, raise a family, and enjoy their happy life.

At least that’s what our culture tells us we should do. We’re taught that monogamy is the “normal” way of living in society, that having multiple partners (polygamy) is somehow unnatural and that we should find ourselves a “soulmate” and settle down.

But monogamy may not be as natural as you think. In fact, according to researchers, our polygamous ancestors weren’t abnormal; if anything, we’re the weird ones in this equation.

The Origins of Monogamy

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Right off the bat, we’ll need to point out that the exact origins of monogamy aren’t well known.

Modern monogamy dates back over 1,000 years, according to evolutionary researchers at University College London. That may sound like a long time, but 1,000 years is just a blip in the evolutionary timeline. Heck, we homo sapiens have existed for 200,000 years or more. Looking at monogamy in that context, it’s practically a new trend in modern society.

But to understand where monogamy came from, we have to look at what came before it.

Competition and Mating

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As polygamy was the norm in primitive societies, our ancestors were used to unceremoniously mating with whomever struck their fancy. It was a rough, tough time, when women had little choice in whom they mated with, and men killed one another to increase their odds of copulating.

In short, there was little in the way of social order, and few records detail the complex social structures of the time. This is part of the reason researchers can’t accurately determine the origins of constructs like monogamy, but academics have come up with a few theories.

Researchers from the University of Tennessee believe that these polygamous societies were dominance-driven hierarchies ruled by the highest-value and most aggressive members of the tribe. Lower-value males had less chance at procreating, and women had little incentive to favor them.

But slowly, things began to change.

A Shift Toward Caring and Protecting

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At some point, these lower-value males realized they could increase their chances of successfully mating by competing in a different way: caring for and protecting their female counterparts. Rather than aggressively copulating without so much as a “how do you do?” this new approach involved wooing potential candidates in a manner more befitting the modern era.

It evolved over the years thanks to the evolutionary advantages it offered. Research suggests that females would have (understandably) preferred this style of courtship, as it left them less open to aggression and provided better resources for raising their children. Along the same lines, this new system of courtship gave less-aggressive males new opportunities to find a mate and pass on their genes, with less need for violent confrontation.

This transition was one of the first steps toward what we might call “monogamy,” though it wasn’t the last.

We Started Farming—And It All Went Downhill

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Another key aspect to monogamy’s rise was the birth of modern agriculture.

While our hunter/gatherer roots forced us to forage and travel around looking for new food, subsistence agriculture allowed us to grow as much as we needed. Thus, we had less incentive to leave our homes and more incentive to hunker down, accumulate wealth, and raise our children in peace.

This drastic cultural shift didn’t happen overnight—modern agriculture is thought to be over 12,000 years old—but in terms of our primitive ancestors, it was an important step away from a life of ongoing hardship that necessitated birthing as many children as possible. Here, men and women weren’t incentivized to compete; they were incentivized to make choices that would produce the best chances of survival for their offspring.

This is about as close to modern monogamy as our ancestors got. And over time, these ideas developed until the concept of the “one partner for one person” family unit became the norm.

Is Modern Monogamy Natural?

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So, with all of that in mind, is monogamy really natural?

Sort of. It’s a young concept in the span of human evolution, but it played an important role in advancing our civilization to where we are today. There’s nothing unnatural about monogamy—just as there’s nothing unnatural about polygamy. Both practices helped shape our evolution in their own way.

And while some may disagree with these interpretations, bear in mind that these are just theories based on our available data. There are no certainties in life, but as time goes on, these theories seem to be plausible as explanations for the modern system of monogamy that we know today.