A thumb signal, usually described as a thumbs-up or thumbs-down, is a common hand gesture achieved by a closed fist held with the thumb extended upward or downward in approval or disapproval, respectively. These gestures have become metaphors in , regardless of whether the gesture was made. History Natural human behaviour While the exact source of the thumb gesture is obscure, several origins have been proposed. Carleton S. Coon, having observed Barbary apes in Gibraltar using the gesture, hypothesised in the anthropological classic The Story of Man that it is a mutual celebration of having opposable thumbs. Critics have suggested, however, that the apes may be simply imitating humans. Ancient Rome The Latin phrase pollice verso is used in the context of gladiatorial combat for a hand gesture used by Ancient Roman crowds to pass judgment on a defeated gladiator. While it is clear that the thumb was involved, the precise type of gesture described by the phrase pollice verso and its meaning are unclear in the historical and literary record. According to Anthony Corbeill, a classical studies professor who has extensively researched the practice, thumbs up signalled killing the gladiator while "a closed fist with a wraparound thumb" meant sparing him. In modern popular culture, necessarily without a historical basis from Ancient Rome, it is wrongly presumed that "thumbs down" was the signal that a defeated gladiator should be condemned to death; "thumbs up", that he should be spared. Middle Ages It has been suggested that 'thumbs up' was a signal from English archers preparing for battle that all is well with their bow and they are ready to fight. Before use, the fistmele (or the "brace height") was checked, that being the distance between the string and the bow on an English longbow. This fistmele should be about , which is about the same as a fist with a thumb extended. The term fistmele is a Saxon word that refers to that measurement. Desmond Morris in Gestures: Their Origins and Distribution traces the practice back to a medieval custom used to seal business transactions. Over time, the mere sight of an upraised thumb came to symbolize harmony and kind feelings. For example in the seventeenth century, see the Diego Velázquez painting The Lunch. 20th century The Oxford English Dictionary cites the earliest written instance of "thumbs-up" (with a positive meaning) as being from Over the Top, a 1917