With his distinctive “hooked” writing style, Barack Obama has become the new poster boy for left-handers. In fact, had Obama lost the presidential race, the White House would still have had a leftie at the helm. John McCain is a left-hander, as is Bill Clinton (plus all the candidates who ran against Clinton in 1992), and George Bush Sr.

The apparent proliferation of lefties in the Oval Office has revived the debate about whether left-handedness is associated with extraordinary accomplishment. According to Britain's leading academic on handedness, lefties, or southpaws, appear to have the edge when it comes to music and mathematics, but there is no hard statistical evidence to suggest that they are favoured in other spheres, such as politics.

Chris McManus, professor of psychology and medical education at University College London, calls the recent run of four out of the past seven American presidents being left-handed “a local blip”. He says: “When you look at American presidents as a whole, or British prime ministers or French presidents or German chancellors, there is no excess of left-handers.” On the other hand, as it were, lefties run a higher than average risk of autism, dyslexia, mental illness and accident. Some health surveys show that they die earlier, too. This darker side of lefthandedness is also evident in language: gauche (French) and sinister (Latin), whereas right, of course, means correct.

McManus, author of the popular science book Right Hand, Left Hand, has become something of a champion for lefties' rights. He calls left-handers the “last neglected minority”; thinks it is scandalous that dangerous machinery is built almost entirely for right-handers; and recently wrote in the British Medical Journal that left-handed surgeons get a raw deal.

He even believes that the census should contain a question on handedness. But he also believes that the lefthanded community goes so far as to “tell lies” about their brethren and how talented they are: “People claim that Bob Dylan is left-handed and Picasso was, but these are urban myths. Some make a virtue out of being left-handed but there's no evidence that left-handed people are more talented in general.”

About one in ten of us - whether presidents or dustmen - is a natural left-hander, with a slight dominance of men (there are five left-handed men for every four left-handed women). The only professions that buck the trend, McManus says, are musicians and mathematicians. Sir Paul McCartney and Sir Isaac Newton are perhaps the most famous embodiments of this thesis. McManus believes that numeracy, musicality and left-handedness could all somehow be part of the same neurological package, and it's down to the way in which the human brain divides its duties between the hemispheres. Language is handled by the left hemisphere; movement by the right.

Gay men (but not lesbians) also sport a higher proportion of lefties than would be expected by chance . This suggests that hormones must be part of the story (autism, too, has been linked to foetal hormones).

There are national differences in the trait: Japan has the fewest left-handers (about one in 25, but rising rapidly), with England (rather than Britain), Belgium and the Netherlands having the most (about one in ten). Social norms are probably at play; left-handers have traditionally been forced to use their right hands, a practice that is, thankfully, dying out.

Handedness has only been observed in human beings and chimpanzees. McManus believes that the genes emerged during the course of human evolution, and stayed in the gene pool because they conferred a survival advantage, although what that advantage was remains unclear. French scientists have suggested that left-handers enjoyed the (pun alert) upper hand in hand-to-hand combat, as it would have been practised in primitive times.

This genetic argument explains why handedness runs in families, including McManus's. The professor is a right-hander; his mother was a left-hander. He has nine-year-old identical twin daughters - and one is a left-hander. He believes that the growing acceptability of left-handedness means that more left-handers are marrying and having children, further spreading the associated genes.

Mind how you hold that pen

When Barack Obama was filmed signing his first official documents as President of the US, his left wrist curling awkwardly over, Mark Stewart was shocked. “I thought - how should I put this politely? - it's not a very good way to hold a pen.” Obama was demonstrating the “hooked” style of handwriting, favoured by a minority of left-handers, in which the paper is held straight and the pen is “pulled” across it from above. “Pushing”, in which the hand remains underneath the script, is regarded as a better technique and places less strain on the wrist.

There is no overall strategy for teaching left-handed children how to write, according to Stewart, who runs courses on the subject (and who owns a shop selling items such as left-handed scissors). Little attention is paid to technique; more to letter formation. As a result, a technique that works with pencils fails with pens, because children smudge their work as they drag their hand across fresh ink.

Stewart, whose youngest son is left-handed, started the courses because his customers regularly complained about their children's battle with handwriting. The repercussions can be severe: a Bristol University study published last month showed that, as a group, left-handers do worse at school.

Stewart says: “I had one woman who said that her daughter no longer wanted to go to school on Thursdays because that was handwriting day. It can affect self-esteem. Yet it takes less than five minutes to show someone how to write without smudging.” He adds that teachers need also to think of other practicalities, such as making sure that left-handers don't knock elbows with right-handers.

You can contact Mark Stewart at mail@lefthand-education.co.uk The charity National Handwriting Association (www.nha-handwriting.org.uk) publishes a pamphlet on handwriting for left-handers.

You've got to hand it to them: Famous left-handers

Napoleon Bonaparte

The reason why most of the world drives on the wrong side of the road. Napoleon overturned the historic practice of travelling on the left with weapons in the right hand when he ordered his armies to the other side to suit his left-handedness.

Fidel Castro

Although ambidextrous, Castro is, perhaps, the ultimate leftie leftie: even on his sick bed in 2007, he insisted on calling into a television show with President of Venezuela Hugo Chavez to hail the fellow left-hander.

Thomas Jefferson

The third American President was the first in a long line of left-handers. Since 1974, two presidents, Jimmy Carter and George W Bush, have been right-handed. Bill Clinton, George Bush senior, Ronald Reagan and Gerald Ford were all left-handed.

Neil Armstrong and Buzz Aldrin

These two lefties earned their places in history as the first men to set foot on the moon in 1969. Their right-handed colleague, Michael Collins, was left on board Apollo 11 to orbit.

Joan of Arc

Handwriting experts have concluded that signatures believed to be Joan of Arc's were written with her left hand. Left-handers have embraced Saint Joan as their own, but sceptics argue that she was simply depicted as a leftie to make her appear evil.

Bart Simpson

Left-handed Simpsons creator, Matt Groening, did his bit for the cause by making Bart, Mr Burns, Ned Flanders, Seymour Skinner and Moe Szyslak lefties. Even Homor Simpson has been seen writing with his left hand.

Julius Caesar

Although left-handed, Caesar introduced the right-handed handshake. Perhaps this was to ensure neither party had an advantage on meeting, their weapon hands taken up. Perhaps it simply benefited Ceaser, who held his weapon in his left hand.

Other left-handers of note:

Alexander the Great

Aristotle

Prince William

Winston Churchill

Henry Ford

Leonardo da Vinci

Charlie Chaplin

Robert de Niro

Osama bin Laden

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