[Hooman Ghayouri]

This Saturday is International Lefthanders day. We kid you not

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This Saturday is International Lefthanders day. We kid you not.

Unlike most daft days though, like Play Your Ukele Day (2nd May) or Town Crier Day (11th July), we think lefthanders are well-worth their own entry in the calendar.

How many lefties are there?

Around ten per cent of the world's population is left handed - that's 640 million-odd people - and there are so many famous lefties whole websites have been set up to list them all.

A bizarrely high percentage of US presidents are southpaws, including Barack Obama, Bill Clinton, Gerald Ford and Ronald Reagan. Ditto ace tyrants Alexander the Great, Julius Caesar and Napoleon.

In the acting world Robert De Niro and Nicole Kidman use their left hands, as do sports stars Pele, John McEnroe and Mike Tyson. Art giants Michelangelo and Leonardo Di Vinci were also left-handed.

No wonder lefties have a reputation for being rather special.

Perhaps the last two chaps explain their reputation for being more creative, but the lucky ten per cent also earn more money according to some studies. This one 7  by the National Bureau of Economic Research, found that left-handed college graduates in the US earned ten per cent more than right handed alumni.

Is it better to be a leftie?

Back in the day lefties also had an advantage in hand-to-hand combat. Because a righty fought with his shield on his left, a left-handed swordsman could make a surprise attack on the opponent's unprotected right side.

In Aztec times lefties were celebrated for their magical and healing abilities, while in Russia, the word levsha (lefty), came to mean 'skilled craftsman'.

Paradoxically however, in other parts of the world our left-handed friends got a raw deal.

Take the Romans. The Latin word 'sinistra' originally meant 'left', but came to represent 'evil' and, eventually, 'sinister' today. Compare that to their word for right-handed – 'dexter' – meaning dexterity or skill. That's just not fair.

Then there's the term 'cack-handed'. For many it means clumsy, but can also stand in for 'left-handed' and derives (apparently) from the ancient tradition of eating with the right hand and, er, wiping oneself with the other.

Crackdown on southpaws

Until relatively recently left-handed schoolkids also had a hard time. As late as the 1960s it was common for British children to have their left hands tied behind their backs and then be forced to use the other hand. The poor mites would then be punished because (duh) their handwriting was shoddy.

Even today, many schools still aren't properly equipped for southpaws, and lack the right scissors, fountain pens and desks, while 'forced conversation' of kids still goes on in countries such as Japan and Taiwan.

With so much cultural baggage around left-handedness, both bad and good, it's not surprising that boffins have been studying the cause for centuries.

So, why are people left handed?

Despite this, the common consensus today is that, well, there is no consensus. Hundreds of causes and factors have been linked to hand preference, but no-one really knows for sure.

One theory is that it's all in the genes.  We spoke to top geneticist Dr Clyde Francks, who helped discover that a particular gene – LRRTM1 - appeared to increase the odds of being left-handed.

The human brain is asymmetrical, which means that the two sides of the brain are used for different functions.

In right-handed people the left side of the brain controls speech and language. According to Dr Francks however, in a "fair proportion" of left-handed people either both sides, or the right side, will control speech instead.

The LRRTM1 gene contributes to this switch-around and influences whether you are left or right handed, amongst many other things.

Dr Francks admits though that genetics only explain around one quarter of the predisposition for left-handedness.

So what about the other 70-odd percent?

Another theory is that environmental factors determine handedness. Some research suggests that the baby's development in the womb, including exposure to hormones, may influence hand preference.

Or perhaps 'modeling' is the cause? Some children choose what hand to use to by copying their parents. This doesn't happen in all cases though.

Does gender play a role?

A child's sex could be another reason. Slightly more boys than girls are left-handed, which lead some researchers to speculate that male hormone testosterone can influence hand preference.
Dr Francks believes all of these theories could possibly decide what hand you use, but only for a tiny minority of people.

"There are no grand explanations," he said. "There are hundreds of different reasons as to why people are left-handed. I believe it's a much more heterogeneous thing."

Myths about the lefthanded

He also says there isn't enough evidence that suggests lefties are more creative or higher achievers.
"It's a myth," he said. "There are numerous scientific studies out there, but typically the sample sizes are too small."

The idea that left-handers are also prone to certain diseases is also ruled out by Dr Francks, even though his research into LRRTM1 suggested carrying the gene slightly increased the risk of developing mental illnesses such as schizophrenia.

"Some people weren't happy about that, but it will only be a tiny influence, it would not be a case that all people with this gene would have a slightly increased risk."

In short then, left-handedness is not, according to all the evidence, something positive or negative, just a "really interesting part of normal human variation".

Don't let this put you off celebrating left-handed day this Saturday however...

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