Humans rank seventh in monogamy among mammals, study finds

Humans are surprisingly committed to pair-bonding — at least compared to our closest living relatives. A new study from the University of Cambridge ranked 35 mammal species by their monogamous tendencies, and we landed in seventh place, ahead of meerkats and white-handed gibbons but trailing behind Eurasian beavers and moustached tamarins.

The researchers didn't ask animals about their feelings. Instead, they analyzed genetic data to measure something more concrete: the ratio of full siblings to half-siblings in each species. The logic is straightforward. Monogamous animals, where two parents stick together, produce offspring who share both parents. Promiscuous species produce more half-siblings. Humans came in at 66% full siblings — meaning full siblings outnumber half-siblings by roughly two to one.

"As anthropologists, we're interested in understanding the variation across human societies, but this is taking a step back and saying, if we were any other species of mammal, we'd be broadly content characterising ourselves as monogamous," said Dr. Mark Dyble, an evolutionary anthropologist at Cambridge.

The findings highlight just how different humans are from our closest genetic relatives. Chimpanzees, which share roughly 99% of our DNA, are largely promiscuous. Gorillas operate a polygynous system where a dominant male mates with multiple females. Both came in at the bottom of the monogamy scale — chimpanzees at 4%, gorillas at 6%.

Why humans went monogamous

Evolutionists have a theory for this divergence. In large-brained primate species, male infanticide — where males kill offspring that aren't genetically theirs — is a real threat. This created two survival strategies. Some females, like bonobos and chimps, use promiscuity to confuse paternity, making it unclear which male fathered which offspring and thus less likely any single male would kill the young. Humans took the opposite route: pair-bonding with a single partner provides paternity certainty, which keeps a father invested in protecting his biological children.

"Both the promiscuity of chimpanzees and bonobos and monogamy in humans are counterstrategies to male infanticide," said Dr. Kit Opie, an evolutionary anthropologist at the University of Bristol.

But here's the catch: human monogamy isn't entirely biological. It's also cultural. Religious traditions, legal frameworks, and social expectations all play a role in keeping pairs together. "If these religions lose their force, serial monogamy, or polygamy by any other name, quickly emerges," noted Professor Robin Dunbar of the University of Oxford.

In other words, our monogamous streak is real — but it's held together by more than just instinct. It's held together by the stories we tell ourselves and each other about commitment.