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Modern humans belong to a small minority of mammals that live monogamously – and rank between the Eurasian beaver and the white-handed gibbon in terms of partner fidelity. This is shown by a comparison of Homo sapiens with 34 other mammal species.
To determine the level of monogamy in a species, evolutionary anthropologist Mark Dyble from the University of Cambridge in England compared sibling data from genetic studies of various mammals. Specifically, he examined the ratio of full siblings to half-siblings – i.e., offspring with only one common parent – among the offspring of the 34 species.
Although this is somewhat crude given the incomplete data, it is the most direct and concrete method of investigation, according to the researcher. The proportion of full siblings in humans is therefore around 66 percent on average. By comparison, the frontrunner – the California mouse (Peromyscus californicus) – has a proportion of 100 percent. The African wild dog (Lycaon pictus) has 85 percent, while the Damara mole rat (Fukomys damarensis) and the Ethiopian wolf (Canis simensis) each have just under 80 percent.
Humans rank between the Eurasian beaver (Castor fiber) at 73 percent and the white-handed gibbon (Hylobates lar) at 64 percent in the list of species included, as Dyble writes in the journal Proceedings of the Royal Society B: Biological Sciences.
Only nine percent of mammals are monogamous
The vast majority of non-monogamous mammals include the black rhino (Diceros bicornis) and the European badger (Meles meles), in which the proportion of full siblings is roughly 20 percent.
At the bottom of the list are the bottlenose dolphin (Tursiops truncatus) with four percent, the orca (Orcinus orca) with three percent, and various macaque species with roughly one to two percent. At the very bottom of the monogamy list is the Soay sheep. Among these feral domestic sheep living on the Scottish island of the same name, full siblings are extremely rare, accounting for only 0.6 percent.
“Monogamy is the dominant mating pattern in our species,” Dyble concludes in a statement from his university. “In contrast, the vast majority of other mammals have a far more promiscuous approach to mating.” According to the study, only nine percent of mammals are monogamous overall.
Monogamy also applies to human societies in which men have multiple wives or women have multiple husbands. “There is enormous cultural diversity in human mating and marriage practices,” says Dyble. “But even the extremes in this spectrum are above what we see in most non-monogamous species.”
The moustached tamarin occupies one of the top spots among monogamous mammals
In contrast to humans, our closest relatives, the great apes, are highly promiscuous: in the eastern gorilla (Gorilla beringei), only around six percent of offspring are full siblings. In the common chimpanzee (Pan troglodytes), the figure is only four percent, similar to dolphins.
The mustached tamarin (Saguinus mystax), which lives in the Amazon region, occupies a top position among monogamous non-human primates. In this species, which belongs to the marmoset family (Callitrichidae), full siblings account for 78 percent of the offspring.
Evolutionary anthropologist Dyble believes that human monogamy has favored the development of large kinship networks. This was the first step toward the creation of large societies and networks of cultural exchange, which in turn were crucial to human success.
- source: red, science.ORF.at/agencies/picture:
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