Are humans naturally monogamous? And does it really make sense to have just one partner?

In a world where dating apps offer endless options and relationship labels continue to evolve, the question of whether humans are naturally monogamous seems more relevant than ever.

Alina, a Romanian woman living in London, found herself wondering the same thing after exploring polyamory — the practice of having multiple intimate relationships with the full knowledge and consent of all parties involved.

"I recently met someone who is poly, and always has been," she explains. "I just wanted to know: Why do we embrace monogamy as a society?"

One way to understand our evolutionary trajectory is to study our closest primate relatives and their reproductive strategies.

"Gorillas are polygamous — one male mates with multiple females," says Kit Opie, an evolutionary biologist at the University of Bristol in the UK. "So the offspring within the group are all conceived by the male, but fathered by different females in the group."

However, this is not an effective reproductive strategy, Opie explains, as it leads to high rates of infanticide.

"Infanticide is a pretty horrific aspect of gorilla life," he says. "It's when a male gorilla kills unrelated baby gorillas so that their mother can become fertile faster and he can mate with her. It's probably not an evolutionary strategy we'd want to emulate."

But among other primates more closely related to humans — such as chimpanzees and bonobos — females have evolved a different evolutionary tactic. Females mate with multiple males, confusing paternity and reducing the chance of their offspring getting hurt.

Humans probably started out with a similar system: mating groups with multiple males and multiple females. But about two million years ago, things changed.

"The reason for this was climate change," says Opie.

"In sub-Saharan Africa, where our ancestors lived, there was a drought and large areas became savannas. Early humans needed to be in large groups to protect themselves from large numbers of predators. Brains got bigger to cope with these large, complex groups and so the lactation period had to be extended."

But with many males in large groups, it became more difficult to confuse paternity.

"In addition, the females needed the help of one of these males to raise the offspring. So, they switched to monogamy."

Is monogamy the best strategy?

According to Opie, this change was necessary not because monogamy was "better," but because it was the only viable option.

Creating human babies with large brains and slow development required a huge investment from parents, more than a mother could make alone.

But while research suggests that early humans evolved to be monogamous, people who choose monogamy often have difficulty remaining faithful to a single partner.

"There are species that stay with a single partner for life and don't cheat, but they are quite rare," notes Opie.

"Our closest relatives that are monogamous are the gibbons. But gibbons are separated from other pairs, and it's probably easier for the male and female to police who's coming into their little patch of rainforest and who isn't."

"But when you're in a large group of multiple males and multiple females, as is the case with humans, it's much harder to police that, to see whether your partner is cheating or not."

Monogamy, from this viewpoint, is less a natural pattern and more a survival strategy—one that came with built-in flaws.

The chemistry of bonding

So what happens in our brains when we fall in love or struggle to stay faithful?

Sarah Blumenthal, a neuroscience PhD student at Emory University in the US, studies prairie voles — small, furry creatures known to form long-term pair bonds, similar to humans.

Unlike their non-monogamous rodent cousins, prairie voles have high levels of oxytocin receptors in the reward centers of their brains.

Oxytocin — often called the "love hormone" — is a neurochemical released in the brain during physical touch and bonding.

"If we experimentally disrupt oxytocin signaling in prairie voles, they are not able to form strong bonds, and they spend less time with their partners," says Blumenthal.

Humans have similar oxytocin systems, which suggests that our brains are designed to experience bonding as rewarding.

But another chemical — dopamine — may explain the shifts in our desire for novelty versus commitment.

During the early stages of bonding, dopamine floods the brain, stimulating attraction and openness. Once the bond is established, dopamine patterns change.

Women with multiple husbands

Despite the evolutionary argument for monogamy, human cultures have always featured a wide variety of relationship arrangements.

Anthropologist Katie Starkweather of the University of Illinois Chicago in the US has documented more than 50 cases of polyandry - when a woman has multiple husbands - around the world, from Nepal and Tibet in Asia to parts of Africa and the Americas.

Although polyandry is statistically rarer than polygyny (one man having multiple wives), Starkweather cautions that it should not be viewed as implausible.

"Women can benefit economically from having multiple partners. If your primary husband died or had to be away for long periods of time—as happened in some Native American groups—you really needed to have a backup plan," she says.

In some cases, non-monogamous arrangements also provided genetic advantages.

“In environments where people get sick a lot and die from diseases, you might do quite well if you have a bunch of kids with a slightly different genetic makeup,” Starkweather explains. “They might be a little bit better suited to the current environment.”

But non-monogamy has its challenges. Maintaining multiple relationships takes time, emotional energy, and negotiation.

"It's extremely difficult to maintain multiple spouses, whether you're a man or a woman. Economically, it's difficult, emotionally, it's difficult. I think that's the main reason why monogamy is still the most common form of marriage statistically," says Starkweather.

The perspective of polyamory

For Alina, monogamy didn’t work out so well in her previous relationship. Now, in a polyamorous relationship, she finds herself dealing with complex emotions.

"Jealousy can be really hard and strong," she admits. "But for me personally, a lot of it can come from feeling like the person isn't being honest with you, and once I know they're being honest, it helps with the feelings of jealousy."

Your partner agrees: "I would say that jealousy is actually not the biggest issue. I would say that the amount of time and effort it takes to maintain multiple healthy relationships can be a bit draining."

However, they both say it’s worth it. “There are no set rules,” Alina says. “It forces you to have conversations you wouldn’t otherwise have—and it’s made our relationship stronger.”

But, after all, are we naturally monogamous? The answer seems to be both yes and no.

Across cultures and throughout history, humans have developed a variety of relationship models to suit their social, economic, and environmental circumstances. For some, non-monogamy offers emotional freedom and economic flexibility. For others, monogamy remains the simplest and easiest way to approach love.

"Humans have evolved to be flexible, and that includes the way we have relationships and the way we marry," says Katie Starkweather. "We live in every type of environment on the planet, and that's because of the flexibility and behavior that we have."