Male bonobos tend to stay with their mothers for life, and for good reason: an adult male bonobo who lives in the same group as his mother is three times more likely to become a father than a male who’s gone his own way, according to a recent study.
That’s likely because bonobo moms, who tend to enjoy high social status, go to extraordinary lengths to make sure their sons mate with fertile females in the group, says a team of primatologists led by Martin Surbeck of the Max Planck Institute for Evolutionary Anthropology in Germany. For example, mothers bring their sons near females in heat, protect them from rival males as they attempt to copulate with these females, and break up copulations between estrous females and rival males.
Bonobo mothers leverage their clout to make sure their sons become fathers.
Surbeck and his colleagues, who observed four bonobo communities in the Democratic Republic of Congo, suspect that moms intervene on behalf of their sons to enhance their own reproductive fitness: the more grandchildren they have, the more likely their genetic material will survive in perpetuity. Similarly, human grandmas in hunter-gatherer societies appear to increase the fertility of their daughters by foraging on behalf of their grandkids; elephant grandmas run their multigenerational families, guiding their grown daughters and grandchildren to food and water and steering them clear of lions; and orca grandmas lead their pods during times of scarcity, homing in on supplies of fish that their daughters and sons may not know about.
Unlike humans, elephants, and orcas, bonobos are “male philopatric”: while males often remain with their moms after reaching maturity, most mature females disperse. So bonobo moms don’t generally have the opportunity to influence the fertility of their daughters, but they can influence the fertility of their sons.
Surbeck and his colleagues also observed another male philopatric species, the chimpanzee, which is closely related to the bonobo. But chimpanzee society differs from bonobo society in that female chimps lack power; all adult males in a group are dominant over all adult females. As a result, chimp mothers can’t effectively advocate for their sons.
Unsurprisingly, the scholars found that a male chimp who lives in a group with his mother is no more likely to sire offspring than a male chimp who doesn’t, and he may even be slightly less likely to achieve fatherhood with his mother around.
Surbeck intends to conduct further studies to establish how and why bonobo females leverage their clout to maximize the mating opportunities of their sons.