Bonobos
He started it! Bonobos shriek when attacked. But they produce different sounds depending on whether this happens with or without provocation. This distinction adds evidence to the idea that they sense when others have treated them unfairly. A bystander sometimes intervenes, supporting or consoling the attacked ape. This could mean that bonobos also take into account the fairness of how others are treated, something so far thought to be limited to humans. When one bonobo attacks another, there is sometimes an obvious reason, such as fighting over food.
On other occasions it appears unprovoked, and in those cases the scream is longer, more high-pitched and harshersounding. “We think these screams are actually eliciting interventions and help from third parties,” says researcher Zanna Clay. “It probably also inhibits the aggressor from doing it again.”