An Anthropologist Made a Mammal 'Monogamy Scale'. Here's Where Humans Rank.

Sticking with a long-term life partner to rear children has long been considered a dominant mating pattern for our species, although reproductive monogamy is not universal across our many cultures and subcultures.

Now, a new study by Cambridge evolutionary anthropologist Mark Dyble ranks Homo sapiens among the top 10 mammal monogamists, using sibling status (full or half) as a proxy for comparing monogamy's prevalence across a range of species.

"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 says.

In fact, humans scored seventh place, with 66 percent of offspring coming from the same two parents, on average.

Related: We Now Have The Largest Ever Human 'Family Tree', With 231 Million Ancestral Lineages

Dyble assessed the distribution of half or full siblings across more than 100 human societies and compared it with equivalent data from 34 other mammal species.

While his method is still only a proxy for reproductive monogamy, Dyble argues it's a more direct way of gauging patterns of monogamy across a spectrum of species and human societies than previous methods.

The human data came from ancient DNA collected from nine different archaeological sites across Europe and Asia (mostly dated to the Neolithic and Bronze Age), and from family trees ethnographers had compiled for 94 pre-industrial human societies.

For the other animals, Dyble rounded up a list of mammal species for which recent genetic data had already been collected with enough detail to show things like reproductive skew (where certain individuals might contribute more to reproduction than others) and kinship composition (the structure of a related family group).

The most monogamous creature of the bunch was, perhaps surprisingly, a rodent, the California deermouse (Peromyscus californicus), with 100 percent full siblings.

The California deermouse, unlike most other rodents, is strictly monogamous. (NNehring/Getty Images)

Across the human societies included in the study, both pre-industrial and prehistoric, 66 percent of siblings shared the same parents, on average.

That's comparable to the rates seen in the study's 10 other socially monogamous mammal species that prefer to parent in long-term partnerships, such as meerkats and Eurasian beavers.

"The finding that human rates of full siblings overlap with the range seen in socially monogamous mammals lends further weight to the view that monogamy is the dominant mating pattern for our species," Dyble says.

Love is free for chimpanzees. (Andreas Last/Getty Images)

We outranked many of our closest primate relatives, however: Mountain gorillas (Gorilla beringei beringei) had a full sibling rate of just 6 percent; chimpanzees, only 4 percent – a level of non-monogamy on par with the notoriously promiscuous dolphins.

Three macaque species also sit near the bottom of the list.

"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," says Dyble.

Of course, sharing the same set of parents with your siblings doesn't quite account for the many forms of non-monogamy humans and other animals are capable of.

DNA records don't account for sexual encounters that do not result in a child, and genealogical studies are limited to the information people choose to record, which may not have included their mistresses or illegitimate children. On the flip side, more detailed records may have been kept in cultures where polygamy is acceptable and enshrined.

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

"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."

Peruse the full list below.

Dyble's 'monogamy league'

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

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