In the wild, male dominance seems to be the norm, but bonobos have a weird male-female relationship. Bonobos share 99% of their DNA with us, and are matriarchal, with female bonobos holding power positions. For example, female bonobos decide who they will mate with and when. Males physically outmatch female bonobos, but they don’t risk forcing aggressive mating moves. Female bonobos also control high-value resources like a fresh kill. They eat while sitting on the ground, while males hover around in branches in hopes of grabbing scraps.
Bonobo males are larger and stronger than females, which gives them an upper hand in attacking, have absolute power in decisions like who should feed first, and in forcing sex. Like almost all other social mammals with larger males, bonobo societies should, in theory, be dominated by males. However, that’s not the case. Until now, scientists had no clue how bonobo females held such powerful spots in the hierarchy of bonobo society. Scientists have now shed some light on the topic and have discovered what makes female bonobos equal, or even more potent than male bonobos. It is their solidarity and ability to form allies that give them the upper hand.
Martin Surbeck from Harvard University and Fruth discovered how female bonobos in the wild maintain their higher spot. This empirical evidence explaining this rare bonobo behavior involves the formation of alliances, or gangs, which the team calls “coalitions”. In 85% of the observed coalitions, females joined forces to target males, forcing them to submit and shape the group’s dominance hierarchy. According to Surbeck, this is the first instance in which females have supported one another to elevate their positions in the hierarchy.
An international team of researchers analyzed 30 years of data from six wild bonobo societies across three field sites in the Democratic Republic of the Congo, the only country where bonobos are found in the wild. The team also recorded and analyzed 1,786 conflicts that occurred between males and females, out of which, females won 1,099 conflicts.
The team had some early hunches about the results. Surbeck thought that a reproductive strategy such as hidden ovulation (ovulation in which no perceptible changes occur) might be the reason females were dominant, as hidden ovulation prevented the monopolization of mating opportunities. The result of coalition formation came as a surprise. Unrelated adult females from different communities, who did not grow up together, unexpectedly formed deep bonds and developed a sense of cooperation. Surbeck, who runs the Kokolopori bonobo research station, notes that coalitions are not often seen forming in the wild.
Female bonobos make a significant impression when forming coalitions. The first signal is deafening screaming, says Fruth. Coalitions form in a matter of seconds in events such as those in which males try to hurt the young. The male is targeted, and female bonobos scream and follow the male through the trees. They can inflict fatal injuries to male bonobos when needed. They are ferocious in asserting their power, and males are better off if they don’t cross any lines, says Fruth.
While females in the study won 61% of conflicts against males and outranked 70% of males on average, this dominance is not a set rule, says Fruth. Females in the bonobo species enjoy a higher status, rather than unchallenged dominance at the top.
Ganging up is just one of many mechanisms likely to drive the dominance and empowerment of female bonobos, the authors say. The fertile window of females is hidden from males, as females show no signs of ovulation during this period. Males can mate by being around female bonobos, rather than forcing themselves on them. According to Fruth, it gives her a glimmer of hope and interest to see females of humans’ closest living relatives in the evolutionary line, teamed up to take the reins of power alongside males.
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