Boing Boing: Snap character judgements:
"The link between facial features and character may be tenuous at best, but that doesn't stop our minds from sizing other people up at a glance,' said Todorov, an assistant professor of psychology. 'We decide very quickly whether a person possesses many of the traits we feel are important, such as likeability and competence, even though we have not exchanged a single word with them. It appears that we are hard-wired to draw these inferences in a fast, unreflective way...'
Why the brain makes such snap judgments is not yet entirely clear, (professor Alex) Todorov said. However, he often works with a sophisticated technological tool for probing brain activity called a functional magnetic resonance imager (fMRI), and Todorov said some of his general research suggests that the part of the brain that responds directly to fear may be involved in judgments of trustworthiness."