Anthropologist's Mammal Monogamy Scale Reveals Human Rank

Understanding Human Monogamy Through a New Lens

Sticking with a long-term life partner to raise children has traditionally been viewed as the dominant mating pattern for humans. However, reproductive monogamy is not universal across all cultures and subcultures. A recent study by Cambridge evolutionary anthropologist Mark Dyble places Homo sapiens among the top 10 mammal monogamists, using sibling status (full or half) as a proxy for comparing monogamy's prevalence across various species.

Dyble’s research highlights that humans rank seventh in this "monogamy league," with an average of 66% of offspring coming from the same two parents. This finding suggests that monogamy remains a significant mating pattern for our species, even though it is not exclusive.

The Methodology Behind the Study

To assess the distribution of full or half siblings, Dyble analyzed data from over 100 human societies and compared it with equivalent data from 34 other mammal species. While this method serves as a proxy for reproductive monogamy, it offers a more direct way to gauge patterns of monogamy across different species and human societies than previous approaches.

The human data came from ancient DNA collected at nine archaeological sites across Europe and Asia, mostly dating back to the Neolithic and Bronze Age periods. Additionally, family trees compiled by ethnographers for 94 pre-industrial human societies were used in the analysis.

For other animals, Dyble gathered genetic data on mammal species that had enough detail to show things like reproductive skew and kinship composition. This allowed for a comparative analysis of how different species approach reproduction and family structures.

Surprising Findings in the Animal Kingdom

Among the mammals studied, the California deermouse (Peromyscus californicus) emerged as the most monogamous, with 100% of its offspring being full siblings. This is followed closely by the African wild dog, with 85% full siblings.

Across human societies included in the study—both pre-industrial and prehistoric—the average rate of full siblings was 66%, which aligns with the rates seen in other socially monogamous mammals such as meerkats and Eurasian beavers.

Humans vs. Primates: A Unique Evolutionary Path

Despite being closely related to primates, humans outperformed many of them in terms of monogamy. Mountain gorillas had a full sibling rate of just 6%, while chimpanzees scored only 4%. These levels of non-monogamy are similar to those seen in dolphins, known for their promiscuous mating habits.

Three macaque species also ranked near the bottom of the list. Dyble notes that based on the mating patterns of our closest living relatives, human monogamy likely evolved from non-monogamous group living, a transition that is rare among mammals.

Limitations and Cultural Influences

It is important to note that sharing the same set of parents with siblings does not fully capture the complexity of non-monogamy in humans and other animals. DNA records do not account for sexual encounters that do not result in offspring, and genealogical studies may miss certain relationships, especially in cultures where polygamy is accepted.

"In most mammals, mating and reproduction are tightly linked. In humans, birth control methods and cultural practices break that link," Dyble explains. "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."

The Full List of Monogamy Rankings

Here is the complete list of species ranked by the percentage of full siblings:

1. California deermouse (100%)
2. African wild dog (85%)
3. Damaraland mole rat (79.5%)
4. Moustached Tamarin (77.6%)
5. Ethiopian wolf (76.5%)
6. Eurasian beaver (72.9%)
7. Humans (66%)
8. Lar (white-handed) gibbon (63.5%)
9. Meerkat (59.9%)
10. Grey wolf (46.2%)
11. Red fox (45.2%)
12. Black rhinoceros (22.2%)
13. European badger (19.6%)
14. African lion (18.5%)
15. Long-tailed macaque (18.1%)
16. Feral cat (16.2%)
17. Banded mongoose (15.9%)
18. Rock wallaby (14.3%)
19. Ringtailed coati (12.6%)
20. Spotted hyena (12%)
21. Eastern chipmunk (9.6%)
22. White-faced capuchin (8.5%)
23. Mountain gorilla (6.2%)
24. Olive baboons (4.8%)
25. Common chimpanzee (4.1%)
26. Bottlenose dolphin (4.1%)
27. Vervet monkey (4%)
28. Savannah baboon (3.7%)
29. Killer whale (3.3%)
30. Antarctic fur seal (2.9%)
31. Black bear (2.6%)
32. Japanese macaque (2.3%)
33. Rhesus Macaque (1.1%)
34. Celebes crested macaque (0.8%)
35. Soay sheep (0.6%)

This research was published in the Proceedings of the Royal Society of London Biological Sciences.