Bonobo Mothers Help Their Sons Find Mates And Have More Sex

A young juvenile male bonobo is groomed by his mom in the Kokolopori Bonobo Reserve. Credit: Martin Surbeck

Talk about interfering with your son’s love life: A bonobo mother will bring her son close to an ovulating female and fend off suitors to give him a leg-up in his mating game. A new study observed four groups of wild bonobos in the Democratic Republic of Congo and seven groups of chimpanzees as a comparison in Côte d'Ivoire, Tanzania, and Uganda. 

The males with maternal match-makers were three times more likely to sire offspring than those without mothers, according to the study published in the journal Current Biology. There’s nothing like having your mom watching over you as you do the deed, it seems.

"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," said lead author Martin Surbeck, a primatologist at the Max Planck Institute for Evolutionary Anthropology, in a statement. "We were surprised to see that the mothers have such a strong, direct influence on the number of grandchildren they get.”

Specifically, the mothers stood guard as their sons mated, they interfered with the mating attempts of other males, and helped their sons be more central in the group and thus nearer to ovulating females. Such bonobo behavior has been documented before, but solid data for how much of a reproductive advantage it provided them with was lacking until now.

"This was a study that combined genetic testing with information about the group composition at many conception dates," Surbeck told IFLScience. "We found that having a living mother in the group increased the likelihood of siring offspring for a bonobo male but not for a chimpanzee male." 

An adult male bonobo in the Kokolopori Bonobo Reserve. Credit: Martin Surbeck

Mothers did not extend the same behavior to their daughters. "In bonobo social systems, the daughters disperse from the native community and the sons stay," said Surbeck. "And for the few daughters that stay in the community, which we don't have many examples of, we don't see them receiving any help from their mothers."

Chimpanzee moms, on the other hand, showed no such interest in their son’s mating life. Bonobos and chimpanzees are closely related, but their social structures differ; bonobos live in mostly matriarchal societies whereas chimpanzees are patriarchal. It’s true that chimpanzee mothers will help defend their adult sons in fights for dominance, but that’s usually where their efforts end.

“Such maternal behavior is more likely to be effective in bonobos, where the sexes are co-dominant and the highest ranks are consistently occupied by females, than in chimpanzees, where all adult males are dominant over all females,” wrote the authors.

Some researchers have noted that the study provides an interesting twist, or nod, to the grandmother hypothesis – essentially why female humans stick around even after menopause. The hypothesis suggests that grandmothers have a better chance of passing on their genes if they help their children care for their offspring. 

When asked whether their research lends support to the grandmother theory, Surbeck told IFLScience "no, not really. However, we find a mechanism in our closest living relatives through which mothers can directly influence their number of grandchildren, so there are additional benefits for her to be alive, even if she doesn't reproduce herself.

"Such indirect fitness gains through support of their offspring (mainly daughters in humans) is, according to the grandmother hypothesis, thought to lead to the post-reproductive lifespan in humans... so a similar mechanism found in one of our closest living relatives."

Looks like the saying "be good to your mother" takes on a whole new meaning in the bonobo world.

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