A new study led by Dr Mark Dyble from the University of Cambridge’s Department of Archaeology has introduced a novel method for measuring monogamy across species, including humans. The research uses genetic data to analyze the proportion of full siblings versus half-siblings as an indicator of monogamous behavior.
Dyble developed a computational model that maps sibling data from recent genetic studies onto known reproductive strategies. This approach aims to provide a more direct measure of monogamy compared to previous methods, which often relied on fossil records or long-term animal observations.
“There is a premier league of monogamy, in which humans sit comfortably, while the vast majority of other mammals take a far more promiscuous approach to mating,” said Dyble.
Despite this ranking, anthropologists have documented significant diversity in human mating systems. Previous studies indicate that 85% of pre-industrial societies allowed polygynous marriages, where one man has multiple wives.
To estimate human monogamy rates, Dyble used genetic evidence from archaeological sites such as Bronze Age burial grounds in Europe and Neolithic locations in Anatolia. He also incorporated ethnographic data from 94 societies worldwide, including groups like the Hadza hunter-gatherers in Tanzania and the Toraja rice farmers in Indonesia.
“There is a huge amount of cross-cultural diversity in human mating and marriage practices, but even the extremes of the spectrum still sit above what we see in most non-monogamous species,” Dyble stated.
The findings, published in Proceedings of the Royal Society: Biological Sciences, show that humans have an overall 66% rate for full siblings. This places humans seventh out of eleven socially monogamous species studied. Beavers rank just above humans with a 73% rate, while meerkats are slightly below at 60%.
The white-handed gibbon closely matches humans with a 63.5% rate and is noted as another “monotocous” species—one that typically produces single offspring per pregnancy. The moustached tamarin ranks higher among primates with nearly 78% full siblings.
Other primates studied exhibit much lower rates; mountain gorillas have a 6% full sibling rate and chimpanzees only 4%, similar to dolphins. Japanese macaques and Rhesus macaques are near the bottom with rates around or below 2%.
“Based on the mating patterns of our closest living relatives, such as chimpanzees and gorillas, human monogamy probably evolved from non-monogamous group living, a transition that is highly unusual among mammals,” said Dyble.
Among canids, grey wolves and red foxes have moderate rates (46% and 45%), while African wild dogs (85%) and Ethiopian wolves (76.5%) score higher for monogamy. The California deermouse tops the list with a perfect score; Soay sheep rank lowest at just 0.6%.
“Almost all other monogamous mammals either live in tight family units of just a breeding pair and their offspring, or in groups where only one female breeds,” explained Dyble. “Whereas humans live in strong social groups in which multiple females have children.”
The Patagonian mara—a large rodent—was identified as another mammal forming stable multi-adult groups with several exclusive pair bonds.
Dyble concluded: “This study measures reproductive monogamy rather than sexual behaviour. In most mammals, mating and reproduction are tightly linked. In humans, birth control methods and cultural practices break that link.”
“Humans have a range of partnerships that create conditions for a mix of full and half-siblings with strong parental investment, from serial monogamy to stable polygamy.”