Mums rule the roost in bonobo society

Mums rule the roost in bonobo society

Young male orcas are mammy’s boys. Instead of leaving to seek his fortune when he comes of age, a young buck stays on in the home pod, where his doting mother pampers him. She leads her son to the best places to feed, and ‘is there for him’ when rival males challenge.

In due course, the golden boy starts visiting other pods for one-night stands with females. His mother’s nurturing now begins to pay off. Big and strong, thanks to her efforts, he gets to father more offspring and, in doing so, helps promulgate her genes.

Pilot whale youths behave like orcas, but the mother-mo-croí fixation was thought to be confined to just those two species. Now researchers at the Max Planck Institute for Evolutionary Anthropology have discovered that it isn’t. In a paper in Current Biology, Martin Surbeck and colleagues claim that young bonobo males and their mothers have similar family arrangements.

In the 1920s, a crate containing early ‘pigmy chimpanzee’ specimens was shipped from Bolobo on the Congo River. The name of the town was misspelt on the shipment and a new noun, ‘Bonobo’, was added to the lexicon.

The Japanese zoologist Takayoshi Kano studied these forest-dwelling primates during the 1970s. ‘Make love not war’, he concluded, is the golden rule in their society. Females mate with all and sundry, even with juveniles and infants. Unusually for mammals other than humans, bonobos even adopt the missionary position in about a third of copulations.

Zanna Clay of Durham University, however, drew more nuanced conclusions following her recent research on the species.

“There is this perception,” she noted, that bonobos “have sex all the time, they are like nymphomaniacs”. In fact, she claims, they are no more sexually active than their cousin, the common chimpanzee.

Given such a permissive regime, it’s impossible for a young bonobo to know the identity of its father. It hardly matters, because this society, like that of the orca, is matriarchal. Powerful females ‘call the shots’; a young male’s standing in the community depends on his mother’s rank.

She defends her son in conflicts with rivals and gives him access, says Surbeck, “to popular spots within social groups in the community”, introducing him to the ‘right’ people.

But despite the bonobo’s anything-goes attitude to sex, there are restrictions on mating. When her son seeks out a female and tries to mate with her, the mother will prevent other males from joining in. She tries to disrupt the mating attempts of young males other than her own.

Surbeck and his co-authors estimate that, by doing so, a mother increases her son’s chance of fatherhood three-fold. Just like orcas and pilot whales, by supporting her son, a bonobo mother is trying to increase the number of grandchildren she will have. It’s all about her, not him.

Bonobos and common chimps are closely related, having shared an ancestor less than a million years ago.

A chimp mother may help her son if he gets into a scrape, but she draws the line at interfering in his sexual encounters. The crucial factor seems to be that, while bonobo society is female-dominated, males rule the roost among chimpanzees.

Martin Surbeck et al. Males with a mother living in their group have higher paternity success in bonobos but not chimpanzees. Current Biology. 2019.

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