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 English: "The audience gave the movie the thumbs-up" means that the audience approved of the movie, regardless of whether the gesture was actually made.
The source of the gesture is obscure, but a number of origins have been proposed.
Natural human behaviour
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[who?] have suggested, however, that the apes may be simply imitating humans.
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. In modern popular culture, it is assumed that "thumbs down" was the signal that a defeated gladiator should be condemned to death; "thumbs up", that he should be spared.
"Now they give shows of their own. Thumbs up! Thumbs down! And the killers, spare or slay, and then go back to concessions for private privies" from Juvenal's Against the City of Rome (ca. 110–127 B.C.)
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 extensively researched the practice, thumbs up signalled killing the gladiator while "a closed fist with a wraparound thumb" meant sparing him.
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 7 inches (18 cm), which is about the same as a fist with 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.[clarification needed] For an example in the 17th century see the Diego Velázquez painting The Lunch.
The Oxford English Dictionary cites the earliest written instance of "thumbs-up" (with a positive meaning) as being from Over the Top, a 1917 book written by Arthur Guy Empey. Empey was an American who served in the British armed forces during World War I. He wrote: "Thumbs up, Tommy’s expression which means ‘everything is fine with me.'"
Popularization in the United States is generally attributed to the practices of World War II pilots, who used the thumbs up to communicate with ground crews prior to take-off. This custom may have originated with the China-based Flying Tigers, who were among the first American flyers involved in World War II. The appreciative Chinese would say ”挺好的“ ("ting hao de"), meaning "very good," and gesture with a thumbs up, which in Chinese means "you're number one." High officials in the Chinese government see it as a sign of respect. Any person from China will recognize this numerical gesture, and it can be seen in movies and photos of the era, though this has not been verified in print by American Volunteer Group (AVG) pilots.
During World War II, pilots on US aircraft carriers adopted the thumbs up gesture to alert the deck crew that they were ready to go and that the wheel chocks could be removed. On modern US carriers, certain deck crew hold a thumb up to signal to the pilot and control tower that their station is OK for take-off. American GIs are reputed to have picked up on the thumb gesture and spread it throughout Europe as they marched toward Berlin. According to Luís da Câmara Cascudo, Brazilians have adopted the "thumbs up" from watching American pilots based in northern Brazil during World War II.
The thumbs up signal has a generally positive connotation in English-speaking countries. However, its perceived meaning varies significantly from culture to culture.
The sign has a pejorative meaning in parts of West Africa, Iran, and Greece according to Roger E. Axtell's book Gestures: The Do's and Taboos of Body Language Around the World. In practice, most Greeks nowadays recognise the positive connotation of the sign due to international exposure. Any perceived pejorative meaning of the past is lost in contemporary use. Despite that, the sign is still very rarely used by native Greeks for its positive meaning (and never for the pejorative).
In Finland, the gesture means "good luck".
The thumbs up gesture is used on the logo of Thums Up soda.
In the United States, American Sign Language users use the thumbs up wiggled modestly left and right to indicate the number ten (10). When held stationary and thrust toward another person the meaning is "yourself". When lifted up by the other palm, the meaning is "help".
On the Internet, and most particularly at the Facebook social media site, the thumbs up gesture is shown as an icon and is associated with the term "like"—which within that context means to follow or subscribe to the page, posts, or profile of another individual or company; and on YouTube, individual videos may be voted on positively or negatively by clicking the thumbs-up or thumbs-down icons respectively (which in some previous versions of the site, used to be acompanied by "Like" and "Dislike" labels, and are still referred as such nowadays), and in the case of a thumbs-up, the video gets added to the user's "Liked videos" playlist. See Like button.
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More recently, these gestures are associated with movie reviews, having been popularized by critics Gene Siskel and Roger Ebert on their televised review show Siskel & Ebert — the thumb up meaning a positive opinion of a film; the thumb down meaning a negative one. The trademarked phrase "two thumbs up", originally meaning a positive review from both reviewers, has come to be used as an indication of very high quality or unanimity of praise.
By extension from the movie review usage, many websites (including Facebook) allow users to approve or disapprove of items, such as comments in a forum, products in a store, or even other people's reviews of movies, books, products, etc., by choosing to click either a thumbs-up or thumbs-down button. In the aggregate, this serves as an evaluation system. Other users may then see the total number of thumbs up and thumbs down given to an item, or may simply see the number which is produced by subtracting thumbs down from thumbs up. (In the latter case, an item which has received exactly ten of each would read as having a rating of zero, rather than one of +10/-10.) Often, users may view a list of items in order of popularity, as ranked by this metric.
Hitchhikers in the West traditionally use a thumbs up gesture to solicit rides from oncoming vehicles, although in this presentation the arm is generally outstretched with the palm and closed fingers facing the motorist. The gesture is also usually performed with the hand nearest the motorist. (However, in one "dialect", the hitch hiker isn't giving a thumbs-up, but is pointing back down the road, to indicate the hopeful destination. A hitch hiker may wave the hand, emphasizing the directional meaning. This is a similar to the "thumb towards the door" gesture, for "get out of here!") 
In scuba diving, the thumbs-up gesture is a specific diving signal given underwater, in which the diver indicates that he or she is about to stop his or her dive and ascend. This occasionally causes confusion in new divers, who might automatically gesture thumbs-up when trying to indicate approval — actually indicating a desire to stop diving and to ascend. The diving signal for approval is the A-ok sign.
Amusement park rides such as roller coasters are usually cleared for departure using a thumbs-up signal from the crew after inspection that all safety precautions have been taken.
Unicode reserves 👍 or U+1F44D symbol and 👎 or U+1F44E symbol for the thumbs up and thumbs down gestures, respectively. A reversed (left-facing) thumbs up gesture is encoded at U+1F592.
|Wikimedia Commons has media related to Thumbs.|
- Carlton S. Coon: "The Story of Man" (1954)
- "James Grout: The Gladiator and the Thumb, part of the Encyclopædia Romana". Penelope.uchicago.edu. Retrieved 2013-07-03.
- "Desmond Morris, Peter Collett, Peter Marsh and Marie O'Shaughnessy, 1979 Webified by Bernd Wechner: Gestures: Their Origin and Meanings, The Thumb Up". Bernd.wechner.info. Retrieved 2013-07-03.
- "Did The Romans Turn Thumbs Down On Gladiators?". News.ku.edu. 1997-09-29. Retrieved 2013-07-03.
- Onion, Rebecca. "Slate: What Does a "Thumbs Up" Mean in Iraq?". Slate. Retrieved 2013-07-03.
- Where Does the 'Thumbs-Up' Gesture Really Come From?, Time
- Hagar, George (1841). Of the Shaft, Ancient and Modern. The Archery Library: Hansard. pp. Chapter 10.
- Toledo, Roberto Pompeu de (March 14, 2007). "Uma paixão dos brasileiros". Veja Magazine (1999): 110.
- Strazny, Philipp (2005). Encyclopedia of Linguistics: M-Z. Fitzroy Dearborn. p. 812. ISBN 1-57958-451-9.
- "Ten". ASL Browser. Michigan State University Communication Technology Laboratory.
- "Yourself". ASL Browser. Michigan State University Communication Technology Laboratory.
- "Help". ASL Browser. Michigan State University Communication Technology Laboratory.
- CBS (2 January 2011). "Roger Ebert's New Voice" – via YouTube.
- Pulver, Andrew (23 June 2016). "'Thumbs down': female critics vastly outnumbered by male counterparts – new study". The Guardian. Retrieved 2 May 2017.
- Wickman, Forrest. "Digit To Ride". slate.com. Retrieved 2 May 2017.
- Feather, Lauren. "Hand signals are the most effective means of communication underwater. Do you know which are the most common?". scubadiverlife.com. Retrieved 2 May 2017.
- "List of emoticons in MSN messenger".
- "Thumb Up / Like Sign Facebook Chat Emoticons Shortcut Keys Code Dislike button". November 3, 2011.