Barbara King examines evidence showing that a basic fact of human nature is that we don't have one:
Anthropological studies show that humans respond with incredible plasticity to the social and environmental forces around us. As biological anthropologist and blogger Patrick Clarkin aptly puts it, our abilities for cooperation and conflict, love and hate are "triggered under given circumstances, facilitated or hampered by social conditions and structures." In a beautiful piece from 2006 for the magazine Foreign Affairs, neuroscientist Robert Sapolsky meshes Clarkin's point with an evolutionary perspective. He argues that even our primate heritage is one of plasticity; small shifts in social dynamics may tip the scales toward violence or peace.