Humans sit somewhere between beavers and white-handed gibbons, with about 66% of siblings being full siblings, a study has found. —JULIAN STRATENSCHULTE/dpa
Modern humans belong to a small minority of monogamous mammals and, in terms of partner fidelity, rank between the Eurasian beaver and the white-handed gibbon.
That's the conclusion of evolutionary anthropologist Mark Dyble of the University of Cambridge from a comparison with 34 other mammal species.
He examined the offspring of these species for the ratio of full siblings to half siblings, that is, those sharing only one parent.
For humans the share of full siblings averages about 66%. For comparison, the world leader in monogamy, the California mouse (Peromyscus californicus), topping the chart at 100% monogamous.
The African wild dog (Lycaon pictus) stands at 85%, and the Damaraland mole-rat (Fukomys damarensis) and the Ethiopian wolf (Canis simensis) each at just under 80%.
Humans rank just below the Eurasian beaver (Castor fiber, 73%) and just above the white-handed gibbon (Hylobates lar, just under 64%), Dyble wrote in the journal Proceedings Of The Royal Society B: Biological Sciences.
When it coms to having full siblings, humans rank just below the Eurasian beaver. —PATRICK PLEUL/dpa
The large majority of mammals are non-monogamous and include the black rhinoceros (Diceros bicornis) and the European badger (Meles meles), each with roughly 20% full siblings.
The tail end of the list includes the bottlenose dolphin (Tursiops truncatus) at 4%, the orca (Orcinus orca) at 3%, and various macaque species at roughly 1% to 2%. At the very bottom stands the Soay sheep, where full siblings account for just 0.6%.
"Monogamy is the dominant mating pattern in our species," Dyble said in a statement from his university.The vast majority of other mammals take a far more promiscuous approach to mating, he said, noting that only 9% of mammal species are monogamous.
Full or half siblings?
To determine a species’ monogamy level, Dyble compared sibling data from genetic studies across mammals.While somewhat coarse given the patchy data, he said it was the most direct and concrete method.
Monogamy applies to humans even in societies where men have multiple wives or women have multiple husbands, it said. There is huge cultural diversity in human mating and marriage practices, Dyble said.But even the extremes in this spectrum are above what we see in most non-monogamous species, he added.
By contrast, our closest relatives, the great apes, show strong promiscuity. In the eastern gorilla (Gorilla beringei) full siblings account for around 6%, and in the common chimpanzee (Pan troglodytes) just 4%, similar to dolphins.
The world leader in monogamy is the humble mouse, one genus of which has an astonishing 100% rate of monogamy, research shows. — SINA SCHULDT/dpa
A high-ranking monogamous non-human primate is the moustached tamarin (Saguinus mystax) of the Amazon. In this callitrichid species, full siblings make up 78% of offspring.
Dyble argues that human monogamy favoured the development of large kin networks. That was the first step towards the creation of large societies and networks of cultural exchange, which in turn were crucial to human success. – dpa
