In humans, the family prevents infanticide. Next to language, the core family, consisting of a mother, a father and children, is the greatest difference between us and other primates.
I describe in 'Chimpanzee Politics' how the alpha male needs broad support to reach the top spot. He needs some close allies and he needs many group members to be on his side.
Most men probably wouldn't want to live the lives of bonobos. They're constantly clinging to their mothers' apron strings. They lack the ability to make decisions about their own fates, something that we and male chimpanzees practically consider our birthright.
Empathy probably started out as a mechanism to improve maternal care. Mammalian mothers who were attentive to their young's needs were more likely to rear successful offspring.
Bonobo studies started in the '70s and came to fruition in the '80s. Then in the '90s, all of a sudden, boom, they ended because of the warfare in the Congo. It was really bad for the bonobo and ironic that people with their warfare were preventing us from studying the hippies of the primate world.