A University of Cambridge study ranks humans among the most monogamous mammals, closer to beavers and meerkats than to chimpanzees. By analyzing sibling ratios across species and human societies, researchers found that long-term pair bonding is unusually prevalent in our species. Even in cultures allowing polygamy, human monogamy exceeds that of most other mammals.
Researchers at the University of Cambridge have developed a new method to measure monogamy across mammal species, placing humans firmly in a select group of socially monogamous animals. The study, led by Dr. Mark Dyble from the Department of Archaeology, uses the ratio of full siblings to half-siblings as a proxy for exclusive mating patterns. This approach draws on genetic data from recent studies and applies a computational model to compare reproductive strategies over time.
Dyble's analysis reveals that humans exhibit a 66% rate of full siblings, ranking seventh out of 11 studied species and aligning with those showing a preference for long-term pair bonds. For comparison, beavers achieve 73%, meerkats 60%, and the white-handed gibbon 63.5%. Among primates, the moustached tamarin stands out with nearly 78%, while closer relatives like chimpanzees score only 4% and gorillas 6%. At the top, the California deermouse reaches 100%, and at the bottom, Soay sheep just 0.6%.
"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," Dyble stated. He noted that human monogamy likely evolved from non-monogamous group living in ancestors similar to chimpanzees and gorillas—a rare shift among mammals.
The research incorporates genetic evidence from ancient sites, such as Bronze Age Europe and Neolithic Anatolia, alongside ethnographic data from 94 societies, including the Hadza of Tanzania and Toraja of Indonesia. Despite 85% of pre-industrial societies permitting polygyny, human full sibling rates remain high. "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 added.
This focus on reproductive monogamy, rather than sexual behavior, highlights how human partnerships—from serial monogamy to stable polygamy—foster strong parental investment. The findings appear in Proceedings of the Royal Society B.