Just how monogamous are humans? Scientists break down how we compare with other animals

By Jack Guy, CNN

(CNN) — Humans are far more monogamous than our primate cousins, but less so than beavers, a new study suggests.

Researchers from the University of Cambridge in England analyzed the proportion of full siblings versus half-siblings across several animal species, as well as various human populations throughout history.

Species and societies that are more monogamous tend to have a greater number of siblings that share both parents, while those that are polygamous or promiscuous produce more half-siblings.

The team of scientists led by Mark Dyble, an evolutionary anthropologist at the University of Cambridge, used a computational model and sibling data produced by genetic studies of humans and other animals to arrive at the estimated monogamy ratings.

They reported their findings in the journal Proceedings of the Royal Society B on Wednesday.

The researchers found that beavers had a monogamy rating of 72%, while humans clocked in at 66%, slightly higher than meerkats’ score of 60%. All three species are part of what they call the “premier league” of monogamy.

At the other end of the scale, dolphins and chimpanzees had a monogamy rating of just 4%, while mountain gorillas came in at 6%.

“This is not the first study to use sibling proportions as a measure of monogamy, but it is the first to compare the rates in humans to other mammal species,” Dyble told CNN.

Monogamy has long been considered a key factor in the social cooperation that has facilitated humans’ ability to dominate the planet, according to the researchers.

Dyble calculated human monogamy rates using genetic data from archaeological sites and ethnographic data from 94 different human societies, underlining that mating and marriage practices vary widely.

“While anthropologists are rightly interested in understanding this diversity, sometimes there is value in stepping back and considering species-wide patterns and how we compare as just another mammal,” Dyble said.

Monogamy ‘premier league’

The average monogamy rating of 66% for humans means we rank seventh out of 11 species included in the study that are said to be socially monogamous, or favor long-term pair bonds.

Dyble added that he was “not surprised” that the average human proportion of full siblings was the same range as other monogamous mammals.

“But where I was surprised was to see the complete separation between humans and non-monogamous mammals: the human societies with the lowest proportions of full siblings (26%) were still higher than the highest ranked non-monogamous mammal species (22%),” he said in an email.

The findings lend weight to the scientific view that monogamy is the dominant mating pattern for humans, said Dyble in a statement published by the University of Cambridge.

Isabel Smallegange, a senior lecturer in population biology at Newcastle University in England, told CNN that the “study uses a clever new way to compare monogamy across mammals.” Smallegange was not involved in the new study.

“The headline finding is striking: humans are much more monogamous than most of our closest animal relatives,” she said.

“Humans sit in the ‘premier league’ alongside species like beavers and meerkats, showing that stable pair-bonding is more common in humans than in related animals such as chimpanzees or gorillas, where multiple mating partners are the norm,” Smallegange added.

“Overall, this research reminds us that while humans are relatively monogamous compared to most mammals, our social success probably stems from a mix of pair-bonding, kin networks and cultural institutions rather than any single mating strategy alone,” she said.

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