Matthew Hutson in The New York Times:
ANGER is a primal and destructive emotion, disrupting rational discourse and inflaming illogical passions — or so it often seems. Then again, anger also has its upsides. Expressing anger, for example, is known to be a useful tool in negotiations. Indeed, in the past few years, researchers have been learning more about when and how to deploy anger productively. Consider a forthcoming paper in the November issue of the Journal of Experimental Social Psychology. Researchers tested the effectiveness of expressing anger in three types of negotiations: those that are chiefly cooperative (say, starting a business with a partner), chiefly competitive (dissolving a shared business) or balanced between the two (selling a business to a buyer). In two experiments, negotiators made greater concessions to those who expressed anger — but only in balanced situations. When cooperating, hostility seems inappropriate, and when competing, additional heat only flares tempers. But in between, anger appears to send a strategically useful signal.
What does that signal communicate? According to a 2009 paper in Proceedings of the National Academy of Sciences, anger evolved to help us express that we feel undervalued. Showing anger signals to others that if we don’t get our due, we’ll exert harm or withhold benefits. As they anticipated, the researchers found that strong men and attractive women — those who have historically had the most leverage in threatening harm and conferring benefits, respectively — were most prone to anger. The usefulness of anger in extracting better treatment from others seems to be something we all implicitly understand.