Only humans have chins: Study shows it's an evolutionary accident‎

Dashiell Hammett mentioned Sam Spade's jutting chin in the opening sentence of his novel, "The Maltese Falcon." Spade's chin was among the facial features Hammett used to describe his fictional detective's appearance, but starting with that distinctive chin was—at least from an evolutionary perspective—an unintentional redundancy, since every chin is distinctive in the sense that humans are the only primates to possess that physical characteristic.