If you’re tired of your parents asking you when you’re getting married, tell them they could be more like bonobos and help you out.

“You’re not going out groomed like that, young man!”
Image via Pixabay.

Many social animals share child-rearing duties among members of the group, but new research from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, found that one species takes this to the extreme: the bonobos. Mother bonobos, the team reports, take an active role in ensuring their sons father children. Sons who are aided by their mothers have three times the chance of becoming fathers compared to those who aren’t.

‘I gave your number to a cute girl’

“This is the first time that we can show the impact of the mother’s presence on a very important male fitness trait, which is their fertility,” says Martin Surbeck, a primatologist at the Max Planck Institute for Evolutionary Anthropology.

“We were surprised to see that the mothers have such a strong, direct influence on the number of grandchildren they get.”

Surbeck and his team worked with populations of wild bonobos in the Democratic Republic of Congo, as well as groups of wild chimpanzees in the Ivory Coast (Tanzania) and Uganda. Both chimpanzee and bonobo mothers would take the role of advocating for their sons in male-on-male conflicts, the team reports — but bonobo mothers also seem to aid their sons in romance.

Some of the behaviors they’ll use to this end include protecting their sons’ mating attempts from other males and intervening in other male’s mating attempts. Bonobo mothers will also leverage their rank in the group (bonobos have matriarchal societies) to give their sons access to popular spots within social groups in the community and help them achieve higher status — which increases their mating prospects. Chimp mothers also engage in such interactions, albeit rarely, the team notes. However, male chimpanzees hold a dominant position over females, socially, making their efforts much less effective than those of bonobo females.

Bonobo mothers don’t seem to extend the same kind of help to their daughters — either socially or romantically.

“In bonobo social systems, the daughters disperse from the native community and the sons stay,” Surbeck says.

“And for the few daughters that stay in the community, which we don’t have many examples of, we don’t see them receiving much help from their mothers.”

In the future, the team wants to understand why bonobo females engage in such behavior. Their working theory so far is that by helping their sons father children, they’re indirectly supporting the continuation of their own genes. This will require a long-term, collaborative effort, he says, to gather data on post-reproductive lifespans of females in chimp and bonobo communities.

“These [bonobo] females have found a way to increase their reproductive success without having more offspring themselves,” Surbeck says.

The team notes that a similar mechanism may have taken place in humans (the ‘grandmother hypothesis‘), listing the long stretch of the post-reproductive human female lifespan as well as the early-age at which human women can no longer bear children (menopause) as evidence in support of this.

The paper “Males with a mother living in their group have higher paternity success in bonobos but not chimpanzees” has been published in the journal Current Biology.