The Science of Smiles

"Chimpanzees sometimes smile not for pleasure or for a social bond, but for power. A dominant chimpanzee will grin and show its teeth. Dr. Niedenthal argues that humans flash a power grin as well — often raising their chin so as to look down at others. 'You're an idiot, I'm better than you'–that's what we mean by a dominant smile,' said Dr. Niedenthal." (NYT)