How many times have you heard the phrase, “Life’s not fair?” And yet, we haven’t let it stop us from trying to make everyone equal. We right wrongs, punish evil-doers, stop injustice. But what explains our urge to retaliate or our need to stick it to Wall Street for the subprime mess? It turns out it’s all in our genes, baby. New York Times science reporter Benedict Carey talks about the evolution behind retaliation, and our primal urge to make the world a little fairer.