In Sparta the schoolmaster punished his pupils by biting their thumbs.
montaigne, “of thumbs”
Isaac Newton thought the thumb alone proved the existence of God.
Pliny attests that the right thumb of a virgin can cause a fallen epileptic to recover.
The classicist Anthony Corbeill relates “the most awful authority of the pollex,” for this is how the ancient Romans called the thumb, with their word for strength, thus distinguishing the thumb from the rest of the hand for its power: “In Roman practice the thumb lived up to its etymological reputation. It could both bestow and withhold favor, grant and deprive life.” In antiquity, “the gesture of infesto pollice, in particular, which seems certain to refer to the erect thumb, was indecorous for the orator and demanded death for the gladiator.” Scanning the crowd for thumbs thrust skyward, like so many middle fingers, the “editor” interpreted the will of the mob: whether a gladiator should slay or spare his opponent. The defeated fighter, in turn, conveyed his request for mercy by raising the index finger, usually of his left hand.
Though “extant evidence . . . indicates that the Romans were unique among Indo-European peoples in identifying at an early stage of their language’s development the thumb’s singularity as a digit,” no direct line of influence can be traced between the current American application of thumbs-up to indicate approval and the Roman use of the upturned thumb to signify certain death….