Monogamy Wasn't Always Normal. . .

Romantically speaking, most people believe we're meant to find the one. But the truth is, for most of history, we were kind of freelancing. Our closest animal cousins don't do long-term pair bonds, and plenty of humans still don't. So when did we start treating just us two as normal? Well, today we're going to find out when exactly humans became monogamous. The question, are humans naturally monogamous? Sounds simple, but it's like asking whether we're naturally into skydiving or reality TV. The short answer is, not exactly. Sociologist Pepper Schwartz once compared humans to geese, a species so monogamous that if one mate dies, the other might never partner again. Humans, meanwhile, tend to move on. Even in the most monogamy-minded cultures, divorce, remarriage, and cheating are common. Which means, if anything, humans are flexibly faithful. More Netflix Renewal than Till Death Do Us Part. And it's not just us. Wolves, beavers, penguins, and even seahorses have been labeled faithful. But most of those species cheat too. Take penguins, nature's supposed lovebirds. In a captive Gentoo colony, DNA testing revealed that about 1.5% of chicks weren't sired by the social father or Magellanic penguins. Where nearly a third of chicks came from extra pair dads. Even prairie voles, the poster child for pair bonding, have litters fathered by multiple males. Turns out, the animal kingdom's basically one big episode of Maury. Humans may not be the most loyal species, but we're definitely the most performative about it. Across the animal kingdom, loyalty comes with choreography. Gibbons, those tree-swinging crooners of Southeast Asia, belt out elaborate duets to mark their territory and each other. A mated pair can spend minutes singing in harmony, the primate equivalent of a power ballad, reminding the jungle that, yes, they're still together. Sandhill cranes do something similar on the ground. Couples perform a unison call, bobbing and trumpeting in sync to strengthen their bond. Albatrosses, meanwhile, turn romance into a Broadway number, clapping beaks, swaying, and bowing in perfectly timed routines that can last half an hour. And the aforementioned prairie voles, the neurochemical mascots of commitment, reaffirm their partnerships through grooming, cuddling, and synchronized nesting, all wired by the bonding hormones oxytocin and vasopressin. Humans? We took that same instinct and built an industry around it. Several, actually. Wedding bows, diamond rings, honeymoon packages, and dating apps. Basically, we invented paperwork and playlists to accomplish what birds and monkeys handle with a dance number. Across the animal kingdom, social monogamy, raising offspring together, has evolved independently in birds, foxes, and even termites. Humans stand out because we mix biology with culture and enforce it with rituals and laws. Our bodies even hint at our romantic history. Human males and females are roughly similar in size, unlike gorillas, where large males monopolize harems. That subtle dimorphism suggests evolution favored pair bonding over dominance. We're not built like silverbacks, but we're not exactly penguins and parkas either. So while the goose may mate for life, humans just schedule couples therapy. Before humans were humans, our primate ancestors were loners, living solo and meeting up to mate before going their separate ways. About 75 million years ago, however, early primates started forming social groups, and with that came new problems. Competition. Infanticide. Insinuating questions about whether you'd jump off a bridge just because your friends did. And of course, the question of who sticks around to raise the kids. Two landmark studies in 2013 tackled this evolutionary puzzle. One, led by Kit Opie at Universal College London, proposed that monogamy evolved in response to infanticide. Males stayed with females to protect their offspring from rival males who might kill infants to bring the mothers back into fertility. The other, by Dieter Lucas and Tim Clutton-Brock at Cambridge, found monogamy often arose when females lived far apart. In those environments, it made more sense for a male to stick with one mate than waste energy searching for others. Different pressures, same result. A shift from one-night stands to longer-term, let's-raise-this-baby alliances. These weren't romantic pairings. Just survival strategies. But they laid the groundwork for the human habit of coupledom. Anthropologist Sarah Blaffer Hardy later expanded on this with her theory of alloparenting. The idea that humans evolved to share child-rearing responsibilities among parents, siblings, and community members. That cooperative model encouraged empathy, bonding, and trust. Grooming rituals, food sharing, and emotional attachment reinforced group survival. In a sense, love began as a survival strategy and turned into a lifestyle. In early human tribes, monogamy and polygamy likely coexisted. Environment shaped the rules. Scarcity pushed partners to pair up. Abundance allowed for competition. Some hunter-gatherer groups even practiced partable paternity, believing multiple men could father the same child. Of course, they can't, but it probably made for a hell of a prehistoric soap opera. Once those early pairs started cooperating, sharing food, protecting offspring, filing joint tax returns, the benefits stacked up. Staying together made life easier. And over generations, that cooperation wired itself into our social expectations. We became serial lovers, biologically primed for bonds, culturally free to break them. Fast forward a few million years. Early human groups got bigger. People started living in tight-knit communities. And new problems showed up. No, we're not talking about how tough it became to find a parking spot, although that probably was a thing. We're talking about disease. Canadian scientist Chris Bauch modeled this in 2016, showing how as societies grew, sexually transmitted infections spread more efficiently. The more people had multiple partners in overlapping time frames, the easier it was for diseases like syphilis or chlamydia to sweep through populations. Some of those infections caused infertility, which made group-wide survival harder. So monogamy, or at least enforced monogamy, became a kind of public health measure. Fewer partners meant fewer pathogens, and cultures that promoted pair bonding had a demographic advantage. The shift to agriculture accelerated this, as humans built permanent settlements. They stopped wandering and started hoarding food, property, and partners. Urban life meant more people in close quarters, more interaction, more hanky-panky, and more potential for disease. But biology wasn't the only motivator. As human societies developed property systems and inheritance rules, pairing up became economically useful too. Marriage linked families, transferred wealth, and stabilized social hierarchies. Anthropologist Joseph Heinrich has argued that widespread monogamy even reduced violence by preventing powerful men from monopolizing women and leaving lower-status men without mates. Basically, love got bureaucratic. It wasn't just who you liked, it was who could help keep your lineage alive, your farm running, and your in-laws happy. In other words, monogamy didn't just cure syphilis, it cured chaos. Once monogamy emerged, it brought perks, especially for dads. By sticking around, males could protect offspring, share resources, boost survival odds, and receive a bottle of aqua velvet every year on Father's Day. That cooperation helped our species' kids thrive, which in turn reinforced the pattern. Over generations, that stability may have even shaped our brains. Kit Opie and others have speculated that committed partnerships encouraged reliable food sharing, particularly protein, which supported the evolution of larger human brains. Obviously, that's great for zombies, because it means bigger meals. But for humans, bigger brains meant longer childhoods, which required even more parental care, a feedback loop that kept families intact. Love, as it turns out, was also chemical. Oxytocin and vasopressin, the so-called bonding hormones, regulate attachment in humans, and yes, even prairie voles. Prairie voles, for the record, are basically the midwestern suburbanites of the rodent world. One partner, shared burrow, joint custody of the grass seeds. Meanwhile, their cousins, the meadow voles, remain charmingly single. So if you're looking to hook up with a vole, try the meadow. Anyway, evolutionary biologists love this contrast because it shows that bonding isn't destiny, it's wiring. And humans have both sets of circuits. Our brains also reward bonding through dopamine and serotonin, the same chemicals behind addiction. For one, this means Robert Palmer really was addicted to love. But it also means falling in love is nature's way of getting us hooked long enough to reproduce. In modern terms, it's like evolution whispering, sure, this'll end badly, but you'll at least raise a few kids first. Once child-rearing became a team sport, culture took over. Monogamy became moralized. Religions and governments began enforcing it, turning what started as a practical arrangement into a moral expectation. By around a thousand years ago, the western idea of one man, one woman for life has solidified through church law, though other systems, from polygamy to polyandry, continued elsewhere. That doesn't mean humans stopped experimenting. Anthropologists note that only about 17% of cultures are strictly monogamous. Most allow some variation. But the general pattern stuck because it worked. Monogamy wasn't universal. It was useful. And for a species that builds everything from families to Netflix queues, useful is close enough to natural. So when exactly did humans decide to be monogamous? Trick question. We never decided. We just kept finding new reasons to double down on it. First came survival pressures. Protect the baby. Avoid disease. Make sure there's enough food to go around. Then came social pressures. Property, peace, and politics. Eventually, monogamy wasn't just practical. It was cultural. We turned it into songs, laws, ideals, and the plot of Pride and Prejudice. Today, technology and globalization are reshaping that story again. Dating apps, social media, and shifting gender norms make monogamy look different. But the goal, stability, is the same. Even new movements, like ethical non-monogamy, echo our old evolutionary flexibility. We've been trying open relationships since before there were houses to open them in. Modern data suggests that around 20-25% of adults have engaged in some form of consensual non-monogamy. We'd be careful before trying that line as a pitch to your spouse. But it's proof that while culture changes, curiosity doesn't. Turns out, till death do us part, now comes with an optional renewal every 18 months. Just like your phone plan. Humans remain what psychologists call biologically polygamous, culturally monogamous. We form deep bonds, but still crave novelty. We build social systems around pair bonding, but break them when they don't fit. Our ancestors built huts and marriage vows for the same reason, to keep the rain out. Whether it's tinder or temple vows, humans just keep finding new ways to make pair bonding work. If anything, monogamy isn't proof that we overcame nature. It's proof that we got creative with it. As always, there are a few fringe hypotheses that go even further. Some scientists speculate that biological parasites, like toxoplasmosis, might subtly influence human bonding and risk-taking behaviors. Others argue that monogamy thrives in environments where economic cooperation is vital, since stability between parents increases survival rates. In other words, whether it's germs or GDP, love is still a numbers game. But the bottom line is, humans are part biology, part culture, and part sheer chaos. Monogamy isn't destiny. It's a strategy we keep revising as our lives, laws, and love stories change. So the next time someone says, monogamy is natural, remind them, so was eating raw meat. Evolution just gave us options.