Affairs dominate TV. Human society is based on monogamy, so are there really that many people who stray? Scientists compared humans with other animals and found that humans ranked near the top for monogamy. We were more similar to beavers and meerkats than to other primates.
Mike Dyble of the University of Cambridge's Department of Archaeology said on the 10th (local time) in the Proceedings of the Royal Society: Biological Sciences that "in a survey of monogamy rates across 35 mammal species, humans ranked seventh in faithfulness to a mate."
◇ Humans' faithfulness, between beavers and meerkats
In nature, many animals practice monogamy like humans. Beavers, foxes, and gibbons are representative examples. Then who is more faithful to a partner? Are some secretly straying? In an affair drama, it ends with a paternity test. Dyble said, "The higher the level of monogamy in a species and society, the more likely it is that siblings share both parents."
Dyble's team analyzed the proportions of full siblings and half siblings in 35 mammal species, including humans. The top of the monogamy ranking was the California mouse. Its offspring were 100% full siblings. African wild dog (85%), Damaraland mole-rat (79.5), moustached tamarin (77.6), Ethiopian wolf (76.5), Eurasian beaver (72.9), and humans (66%) followed.
In faithfulness to a mate, humans were closer to beavers and meerkats (59.9) than to other primates. Chimpanzees, the closest primates to humans, were at just 4.1%. Baboons (3.7) and rhesus macaques (1.1) were at the bottom of the monogamy ranking.
Scientists inferred human sexual selection by studying fossils of early humans and today's hunter-gatherer societies. For wild animals, they studied mating systems through long-term observation and paternity tests. Dyble analyzed the proportions of full and half siblings in mammal groups, including humans. He said, "These results show that monogamy is the dominant mating pattern of our species."
◇ A mating evolution different from chimpanzees and gorillas
Debate over human monogamy has continued for centuries. The prevailing claim has been that monogamy is the cornerstone of social cooperation that enabled humanity to dominate the Earth. But anthropologists have continued to find different cases in human societies. For example, earlier research found that 85% of preindustrial societies allowed polygyny, in which one man simultaneously marries multiple women.
To calculate humans' monogamous faithfulness, Dyble examined genetic analyses of fossils from archaeological sites. He also used ethnographic data from 94 human societies worldwide, ranging from the Hadza hunter-gatherers in Tanzania to the Toraja rice-farming group in Indonesia.
Dyble said, "Given the mating patterns of our closest primate relatives such as chimpanzees and gorillas (6.2%), humans likely began with multiple mates like other mammals and later evolved into monogamy." In fact, fossils from an early Neolithic site in the Cotswolds in England showed a full-sibling rate of just 26%, but four later Neolithic groups in northern France were 100% full siblings.
Humans are thought to have evolved monogamy as a survival strategy to protect offspring. Kit Opie, an evolutionary anthropologist at the University of Bristol, said, "Human societies are close to chimpanzees and bonobos, but simply chose a different path in mating," adding, "Differences in mating form are a response strategy to male infanticide, a serious problem in primate species with large brains." Female chimpanzees and bonobos mate with multiple males to create paternity uncertainty and protect their young, while humans ensure paternity so that males protect their offspring.
In this study, the species most similar to humans was the white-handed gibbon, ranked eighth, with a full-sibling rate of 63.5%. The white-handed gibbon was the only "singleton-bearing" species among the top monogamous species. Unlike other monogamous mammals that typically have multiple young per birth, it generally bears one offspring per pregnancy.
The only nonhuman primate in the top ranks was the moustached tamarin in fourth place. It is a small monkey living in the Amazon rainforest and usually gives birth to twins or triplets.
References
Proceedings of the Royal Society: Biological Sciences (2025), https://royalsocietypublishing.org/rspb/article/292/2060/20252163/363965/Human-monogamy-in-mammalian-context?searchresult=1
Human Behavioral Ecology (2024), DOI: https://doi.org/10.1017/9781108377911.011