Spite-- It makes us US! From a LiveScience.com article by Chucky Choi*: "Spite is a dark emotion that nonetheless seems to help set humanity apart from its closest primate relatives, new research suggests.
"The sinister emotion that angrily dwells on how unfair the world is could shed light on the unusual human notion of fair play, and scientists say the research could help understand how and why these dark and light sides of human nature evolved." (For the rest of the article, go here.)
* He goes by "Charles Q.", but I call him Chucky to spite him.