Image caption Whether or not M.I.A. was aware, the gesture originally referred to a phallus

An American television network has apologised after pop star M.I.A. extended her middle finger during Sunday night's Super Bowl halftime show. What does the gesture mean, and when did it become offensive?

A public intellectual, expressing his contempt for a gas-bag politician, reaches for a familiar gesture. He extends his middle finger and declares: "This is the great demagogue."

The episode occurred not on a chat show nor in the salons of New York or London, but in 4th Century BC Athens, when the philosopher Diogenes told a group of visitors exactly what he thought about the orator Demosthenes, according to a later Greek historian.

The middle finger, extended with the other fingers held beneath the thumb, is thus documented to have expressed insult and belittlement for more than two millennia.

'Phallic gesture'

Ancient Greek philosophers, Latin poets hoping to sell copies of their works, soldiers, athletes and pop stars, schoolchildren, peevish policemen and skittish network executives have all been aware of the gesture's particular power to insult and inflame.

"It's one of the most ancient insult gestures known," says anthropologist Desmond Morris.

"The middle finger is the penis and the curled fingers on either side are the testicles. By doing it, you are offering someone a phallic gesture. It is saying, 'this is a phallus' that you're offering to people, which is a very primeval display."

During Sunday night's broadcast of the Super Bowl, America's most-watched television programme of the year, British singer M.I.A. extended the finger during a performance of Madonna's Give Me All Your Luvin'.

Image caption Diogenes of Sinope was reputedly a fan of the middle-finger gesture

The NFL and NBC television, which broadcast the game and the half-time show, apologised.

"The obscene gesture in the performance was completely inappropriate," said Brian McCarthy, a spokesman for the NFL.

The gesture is widely known to Americans as flipping the bird, or just giving someone the finger.

The Romans had their own name for it: digitus impudicus - the shameless, indecent or offensive finger.

In the Epigrammata of First Century AD by the Latin poet Martial, a character who has always enjoyed good health extends a finger, "the indecent one", at three doctors.

Monkeys' obscene gesture

The Roman historian Tacitus wrote that German tribesmen gave the middle finger to advancing Roman soldiers, says Thomas Conley, a professor emeritus of communication and classics at the University of Illinois, who has written about the rhetoric of insults.

Image caption They may look innocent, but these squirrel monkeys are capable of their own obscene gesture

Earlier, the Greeks used the middle finger as an explicit reference to the male genitalia.

In 419BC, the playwright Aristophanes puns in his comedy The Clouds about dactylic (finger) rhythm, with a character gesturing first with his middle finger and subsequently with his crotch.

The gesture's origins may extend even further back: male squirrel monkeys of South America are known to gesture with the erect penis, says Dr Morris.

The middle finger, which Dr Morris says probably arrived in the US with Italian immigrants, is documented in the US as early as 1886, when a pitcher for the Boston Beaneaters gave it in a joint team photograph with the rival New York Giants.

Expression of 'displeasure'

The French have their own phallic salute, says Dr Morris.

In performing the "bras d'honneur" (arm of honour), one raises the forearm with the back of the hand facing outward, while slapping or gripping the inside of the elbow with the other hand.

The British gesture - the two-fingered "v" with the palm facing inward - is a "double phallus", Dr Morris quips.

Image caption The legend that the "two-fingered salute" stems from the Battle of Agincourt is apocryphal

Although scholars and historians continue to debate its origins, according to legend it was first displayed at the battle of Agincourt in 1415, although this is widely regarded as mythology.

The story goes that English soldiers waved their fingers at French soldiers who had threatened to cut off captured archers' first two fingers to prevent them shooting arrows. The English were thus boasting they were still capable of doing so.

The middle finger's offensive meaning seems to have overtaken cultural, linguistic and national boundaries and can now be seen at protests, on football pitches, and at rock concerts across the world.

In December, Liverpool striker Luis Suarez was photographed giving an American-style middle finger to Fulham fans after his club's 1-0 loss there.

The FA cited him for improper conduct and suspended him for one game.

Protest, rage, excitement

In 2004, a Canadian MP from Calgary was accused of pointing his middle finger at a member from another party who he said had been heckling him in the House of Commons.

"I expressed my displeasure to him, let's put it this way," Deepak Obhrai told a Canadian newspaper.

Two years earlier, pop star Britney Spears gave the finger to a group of photographers in Mexico who she complained had been chasing her. Some of her fans thought the gesture was aimed at them, and Spears later apologised.

While the middle finger may historically have symbolised a phallus, it has lost that distinctive meaning and is no longer even obscene, says Ira Robbins, a law professor at American University in Washington DC, who has studied the gesture's place in criminal jurisprudence.

"It does not appeal to the prurient interests," he says.

"This gesture is so well ingrained in everyday life in this country and others. It means so many other things, like protest or rage or excitement, it's not just a phallus."

And he rejects an Associated Press journalist's characterisation of the gesture as "risque".

"What is risque about it? Maybe the dancing was risque, but the finger? I just don't see it."