Thousands of hours of observing communities of both species dismantle the peaceful image of the former. males triple the aggression rate of the latter when the victim is another male.

Only in 16% of the cases was it an attack on a female, almost identical to that observed in the opposite direction, from a female to a male. Female bonobos are co-dominant with males and can form coalitions against them. In chimpanzees, males outrank all females. They sexually force them to mate with them and therefore act aggressively against them, says researcher Maud Mouginot. The key is mating, she says: “The aggression of males against females is much lower in bonobos and they do not use it in the context of mating’s significance’” The research was published in the journal Current Biology, which is open-access and free to read on the website of the University of Massachusetts, Amherst, and the journal of the Royal Society of London, which published the study in January.