The popular belief that ancient Romans used thumbs up and down gestures to determine a gladiator's fate is largely inaccurate. Historical evidence suggests a more complex system of hand signals was used in gladiatorial contests. The Latin phrase "pollice verso" (turned thumb) is ambiguous and does not specify a particular direction1. Some scholars, like Anthony Corbeill, argue that a thumbs-up gesture may have actually signaled death, while a closed fist with the thumb pressed against it indicated mercy12. The modern interpretation of thumbs up meaning approval likely stems from a misunderstanding of Roman gestures, popularized by Jean-Léon Gérôme's 1872 painting "Pollice Verso"4. This painting, which depicted spectators giving thumbs-down gestures to condemn a gladiator, significantly influenced popular culture and even inspired scenes in the film "Gladiator"45. In reality, the exact nature of these gestures remains uncertain due to limited historical evidence.

During the Middle Ages and Renaissance in Europe, the thumbs-up gesture took on new meanings and uses. One notable practice was the custom of sealing business transactions or agreements by extending thumbs upward. Two parties would wet their thumbs and then press them together, held upwards, as a sign of friendly agreement or approval4. This practice likely contributed to the modern association of the thumbs-up gesture with positive affirmation. Additionally, English archers reportedly used the gesture to signal readiness for battle, as the distance between the bowstring and the bow (the fistmele) was measured using a fist with an extended thumb1. These historical uses helped shape the gesture's positive connotations in Western culture, laying the groundwork for its widespread adoption as a symbol of approval in later centuries.

The widespread adoption of the "thumbs up" gesture as a symbol of approval or success gained significant momentum during World War II, particularly among American military personnel. Fighter pilots on US aircraft carriers used the thumbs up to communicate their readiness for takeoff to deck crews, signaling that wheel chocks could be removed1. This practice may have originated with the China-based Flying Tigers, who were among the first American flyers involved in World War II1. The gesture was easily visible from the cockpit and quickly understood by ground personnel, making it an effective form of non-verbal communication in noisy environments. As American soldiers spread across Europe during the war, they likely contributed to the gesture's widespread adoption beyond military contexts5. The thumbs-up sign, carrying the cool bravado associated with fighter pilots, appealed to many and rapidly spread, eventually becoming a universal symbol for approval, readiness, and positivity in Western culture3.

The thumbs-up gesture carries diverse meanings across cultures, highlighting the importance of cultural awareness in non-verbal communication. In Western cultures, it is widely recognized as a positive sign indicating approval or agreement.12 However, its interpretation varies significantly in other parts of the world. In some Middle Eastern and West African countries, the gesture can be considered offensive or insulting.13 In Japan, while generally understood as positive due to Western influence, it can also be used to indicate the number five.4 The gesture's meaning can even differ within Western cultures; for instance, in Australia, it may mean "okay" or "good job," similar to its American usage.2 These cultural variations underscore the need for caution when using hand gestures in international settings to avoid unintended offense or misunderstandings.