On the evolution of human emotions:

“Emotional flexibility means that we could spread our feelings around promiscuously, extending them to our fellow humans in general and sustaining loyalties over great expanses of time. By comparison, other animals seem strictly concerned with specific threats and benefactors. We might have evolved our emotional plasticity in part because our brains keep developing for so long after our birth, and so the social environment constitutes a huge part of our mental and emotional formation. Our emotional systems had to be fluid, flexible, and general; they couldn’t just fasten on one animal or action pattern. But these stretchable emotions probably helped our social evolution as much as language and symbol manipulation ever did.”