Beavers, more monogamous than humans: study

Madrid. Humans are much closer to meerkats and beavers in terms of exclusive mating than to most of our primate cousins, according to a new study from the University of Cambridge (United Kingdom) that includes a table that ranks rates of monogamy in several mammal species.

The study, published in Proceedings of the Royal Society: Biological Sciencesputs humans at an overall rate of 66 percent full siblings, putting us in seventh place out of the 11 species in the study considered socially monogamous and preferring long-term pair bonds.

Previous evolutionary research has used fossil records and anthropological fieldwork to infer human sexual selection. Meanwhile, in other species, researchers have made long-term observations of animal societies and used paternity tests to study mating systems.

Now, a new approach by Dr Mark Dyble of Cambridge’s Department of Archeology looks at full-sibling and half-sibling ratios in a large number of species, as well as in various human populations throughout history, as a measure of monogamy.

Species and societies with higher levels of monogamy are likely to produce more siblings who share both parents, Dyble says, while those with more polygamous or promiscuous mating patterns are likely to have more half-siblings.

Data collection

The expert devised a computational model that maps sibling data collected from recent genetic studies on known reproductive strategies to calculate an estimated monogamy score.

To assess rates of human monogamy, Dyble used genetic data from archaeological sites, including Bronze Age cemeteries in Europe and Neolithic sites in Anatolia, as well as ethnographic data from 94 human societies around the world: from the Hadza hunter-gatherers of Tanzania to the Toraja rice farmers of Indonesia.

Meerkats have a monogamous reproduction rate of 60 percent, while beavers surpass humans in monogamy, with 73 percent. As in the case of humans, this suggests a significant tendency towards monogamy in these species, but with considerable flexibility.

The white-handed gibbon is the most similar to humans in the study, with a monogamy rate of 63.5 percent. It is the only other species with a higher classification of “monotonic,” meaning it typically has one offspring per gestation, unlike the litters of other monogamous mammals.

The only other non-human primate in the top division is the mustached tamarin: a small Amazonian monkey that usually produces twins or triplets and has a full-sibling rate of nearly 78 percent.

All of the other primates in the study are known to have polygynander or polygynander mating systems (in which both males and females have multiple partners) and rank very low on the monogamy table.

Mountain gorillas reach a complete reproduction rate of 6 percent, while chimpanzees reach only 4 percent, the same level as dolphins. Several macaque species, from the Japanese (2.3 percent) to the rhesus (1 percent), rank near the bottom of the table.

Among the few animals with a similar evolutionary change are the wolf and fox species, which have a degree of social monogamy and cooperative care, while the ancestral canid probably lived in groups and was polygamous.

The gray wolf and red fox sneak into the top league with full sibling rates of almost half (46 and 45 percent, respectively), while African species have much higher rates: the Ethiopian wolf hits 76.5 percent and the African wild dog comes in second for monogamy with a rating of 85 percent.

Topping the chart is the California deer mouse, which maintains its mate for life, with a rating of 100 percent. In last place is the Soay sheep from Scotland, with 0.6 percent full siblings, as each ewe mates with several rams.