According to IFL Science, a research team analyzed three groups of bonobos in the Kokolopori Bonobo Reserve in the Democratic Republic of Congo and two chimpanzee communities in Gombe National Park in Tanzania.
Eleanor Higgs
For the study published in the journal Current Biology, the researchers focused on 12 bonobos and 14 chimpanzees within these groups and followed these individuals for entire days, noting how often they had aggressive interactions and with whom.
They also studied whether the interactions involved fighting or biting or whether they were non-physical.
"We go to the nests and wait for them to wake up and we follow them all day long - from the moment they wake up to the moment they go to sleep at night - and we record everything they do," says Maud Mouginot, anthropologist and lead author, currently at Boston University.
The researchers found that, contrary to their expectations, male bonobos were more aggressive than chimpanzees.
Bonobos had 2.8 times more aggressive encounters and three times more physical interactions, with higher rates of female-male and male-male aggression than chimpanzees.
Male bonobos were practically only aggressive towards other male bonobos, while chimpanzees were also aggressive towards females.
Male chimpanzees were usually aggressive in groups of males - which the researchers think may be part of the reason why chimpanzees were considered less aggressive overall.
"The idea is not to invalidate the image that bonobos are peaceful, but rather that there is more complexity in both species," continued Mouginot.
These groups of males, known as "coalitions", have the potential to cause more injuries and weaken the group as a whole against threats.
Bonobos, on the other hand, almost exclusively had one-on-one interactions, but were never observed killing each other and are not thought to fight over territory.
"Chimpanzees and bonobos use aggression in different ways and for specific reasons," says Mouginot.
In both chimpanzees and bonobos, it seemed that the more aggressive the male, the more successful he was at mating. This was extremely surprising in both species, as they have very different social structures.
In chimpanzee communities, male-dominated hierarchies can form coalitions that force females to mate. However, in bonobo groups, females outnumber males in a codominant social dynamic.
The team found data showing that the two males with the highest rate of contact aggression in the Kokolopori bonobos had sired 80% of the offspring.
"Male bonobos that are more aggressive get more copulations with females, which is something we didn't expect," said Mouginot.
"This means that females don't necessarily opt for nicer males."
