A comparative analysis of chimpanzee and bonobo brains has shed some light on human social behavior. Not surprisingly, human behavior is between bonobos and chimpanzees, with the average human male closer to bonobos in behavior, but status-striving males closer to chimpanzees. I will also note that sociopaths are almost identical to chimpanzees in behavior. In any case, humans vary between the two.
The first article notes that bonobos separated off from the chimpanzee line after the chimpanzee/bonobo line split from what would become humans. I doubt that. There is good evidence that chimpanzees split from the human/bonobo line, and then the humans and bonobos split. Superficially bonobos look more like chimpanzees than humans, but the fact that bonobos share several neotenous traits with humans, including vaginal angle (allowing for more comfortable face-to-face copulation), suggests such a branching. This would also make sense of the similarities in brain activity/behavior as well as the fact that bonobos are genetically closer to humans than are chimpanzees.
What does all of this have to do with literature? Well, if we understand the fact that humans behaviorally are between chimpanzees and bonobos, then it suggests we should try to understand both species to understand better our own. Perhaps we can make more sense of characters' behaviors by understanding their closeness to chimpanzee or bonobo behavior.