Out in the wild, countless animal societies are governed by males. That's why scientists have long puzzled over those in the animal kingdom that are female-dominated, whether they consist of elephants, honeybees, or, most recently, bonobos. Why, a new study asks, do female bonobos reign supreme, even when male bonobos are so much bigger, louder, and stronger? Turns out the arrangement has a lot to do with solidarity.
For nearly three decades, between 1993 and 2021, a group of researchers closely tracked six wild bonobo communities in the Democratic Republic of the Congo in an attempt to determine exactly how female bonobos asserted their dominance over males. The resulting study, which was published in Communications Biology on April 24, concluded that females would band together to maintain authority.
"We have found what everybody already knows -- that when you work together, you're more successful and you gain power," Martin Surbeck, a behavioral ecologist at Harvard University and lead author of the study, told National Geographic.
Unlike many other species, such as chimpanzees, female bonobos are often those with priority access to food resources, those deciding when and with whom to mate, and typically outrank males in their social hierarchies. The study revealed that, to retain these privileges, female bonobos form coalitions of about three to five members. In 85% of cases, the coalitions would collectively target male bonobos to gain power, and in 61% of these fights, female bonobos proved victorious.
"To our knowledge, this is the first evidence that female solidarity can invert the male-biased power structure that is typical of many mammal societies," Surbeck said in a statement. "It's exciting to find that females can actively elevate their social status by supporting each other."
Exciting as they may be, these results actually came as a surprise. Before parsing their data sets, Surbeck and his team considered several hypotheses, such as hidden ovulation, which prevents males from monopolizing mating opportunities. Adult females must migrate to mate, and so, during these moments, they join communities in which they didn't grow up, making the deep bonds and cooperation within these coalitions unexpected.
The female coalitions are "ferocious," according to Barbara Fruth, who has led the LuiKotale bonobo research station for 30 years. The bonobos can scream so loud "you have to block your ears," Fruth claimed, chase males up trees, and, at times, cause fatal injuries, especially if there's a threat posed to chimps.
"You know why these males don't try to overstep boundaries," Fruth added.
In bonobo societies, females outrank 70% of males on average, but their dominance is by no means the rule. Female dominance varied in each population along a spectrum, with coalitions offering just one mechanism to drive empowerment.
"It's more accurate to say that in bonobo societies, females enjoy high status rather than unchallenged dominance," Fruth said.
Regardless, as one of our closest living relatives, bonobos do provide insight into the evolution of social hierarchies.
"[Our findings] tell us that male dominance and patriarchy is not evolutionarily inevitable," Surbeck continued in National Geographic. "This reinforces the idea that apes and humans are very innovative and flexible in their behavior. If anything, I think we can say that it does give us some hope."
Laura Simone Lewis, a biological anthropologist at the University of California, Berkeley, who was not involved in the study, echoed Surbeck's sentiment in the Washington Post: "This study could provide insight into how women could build power to better protect ourselves from male violence -- by forming and maintaining coalitions, or alliances, with one another, just like our bonobo cousins."
Following this study, researchers are, of course, eager to discover more about bonobos and the complexity of their societies. To accomplish this, however, the primates must be protected in the face of climate and habitat destruction.
"Bonobos are an endangered species," Surbeck told the New York Times. "As our closest living relative, they help us look into our past. If we lose them, we lose a mirror for humanity."
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