It's a widely recognized gesture: fingers curled into the palm, thumb stretched out, pointing skyward. But what's the history of the gesture and how did it come to mean "yes" or "O.K."? First off, the idea that the up- or downturned thumb originated as a gesture that would save or cost a gladiator's life in Ancient Rome — an idea popularized by the movie Gladiator — isn't quite right. It's not that gestures wouldn't have been used to communicate such ideas, but rather that the Romans used a wide visual vocabulary in which the meanings of certain movements were different from their modern implications. The thumbs-up sign that today means "O.K." in that lexicon expressed disapproval.