Looking to the left

Albert Einstein, John Dillinger and Laboratory News staff writer Kerry Taylor-Smith – an unusual bunch, but what do they have in common? They’re all left-handed. Here we look at the science of the southpaw Being left-handed can be a curse and a blessing. Left-handers are historically thought to be more creative and some of the most successful people were or are left handed: Marilyn Monroe, Sir Paul McCartney, Albert Einstein – even Queen Victoria and Barak Obama. But research and history also teaches us that lefties – as we’re affectionately known – are more prone to learning and mental disorders, and even have criminal tendencies like John Dillinger, Jack the Ripper and Billy the Kid.

As a leftie myself – with two left-handed parents but a right-handed brother – this issue of what determines a person’s tendency to be left- or right-handed is intriguing. I know the right side of the body is controlled by the left side of the brain and vice versa. If the left side of the brain is more developed, then a person is likely to be right-handed – but why?

Neurologist Norman Geschwind proposed that your handedness is decided before birth1. He believed left-handed people were exposed higher levels of testosterone during development. According to the Geschwind theory, variations in the levels of testosterone during pregnancy shape the foetal brain – testosterone suppresses growth of the left cerebral hemisphere so more neurons migrate to the right, leading to the child being left-handed.

Geschwind tied his theory of left-handedness into the increased risk of auto-immune disorders, learning disorders and dyslexia – a hypothesis which has been widely studied.

NOTABLE LEFTIESScientists: Benjamin Franklin, Leonardo Da Vinci, Sir Isaac Newton, Albert Einstein, Marie Curie Royals: Queen Victoria, Prince Charles and Prince William Actors/actresses: Tom Cruise, Steve McQueen, Marilyn Monroe, Angelia Jolie Sportspeople: Maradona, Pele, Brian Lara, John McEnroe, Martina Navratalova Others: Buzz Aldrin, John F Kennedy Jnr, John Dillinger, Lewis Carroll, Kurt Cobain, Jimi Hendrix and Bart Simpson

Similarly, Stanley Coren, a psychologist from the University of British Columbia believes a person’s tendency to be left-handed can be decide before birth. Evidence has shown a link between trauma during gestation or birth, and pathological left-handedness2. The mother’s age could also play a role – women over 40 at the time of their child’s birth are 128% more likely to have left handed babies than a woman in their 20s.

“Handedness is controlled by a whole lot of pathways in the brain and if any one of these pathways is mucked up during gestation, then handedness becomes a cosmic dice game,” Coren said. “We believe this accounts for about half of all left-handers.”

About 10-12% of the human population are left-handed and lefties are more likely to have a left-handed relative – in my case, both my parents, and my maternal great-grandmother – so is there a gene for left-handedness?

In 2007 researchers from the University of Oxford discovered a gene which appears to increase the odds of being left-handed3. The gene plays a key role in controlling which parts of the brain take control of specific functions – namely speech and emotion.

The left side of the brain usually controls speech and language in right-handed people, while the right side controls emotions. However, in left-handed people, the opposite is often true, and researchers believe the gene LRRTM1 is responsible for the switch.

Dr Clyde Francks, who led the research said: “We hope this study’s findings will help us understand the development of asymmetry in the brain. Asymmetry is a fundamental feature of the human brain that is disrupted in many psychiatric conditions.”

The researchers believe LRRTM1 – as well as increasing your chances of being a leftie – slightly raises the risk of developing mental illness, in particular schizophrenia. Francks does, however, point out that the precise role of LRRTM1 is still unknown and that there are many other reasons why people develop mental disorders.

Scientists from the Wellcome Trust for Human Genetics – based at the University of Oxford – identified a novel gene for left-handedness in 20104. The gene also provides the first genetic evidence to support a link between handedness and dyslexia.

The genomes of 192 children with reading difficulties were scanned, and they also had their left and right hand skills measured. The scientists found a strong link between a variant of the gene PCSK6 and relative hand skill – those who carried the variant were, on average, more skilled with their right hand compared to the left than those not carrying the variant.

The protein product of PCSK6 interacts with another protein called NODAL, which plays a key role in establishing left-right asymmetry early in embryonic development. This suggests genetic variants of PCSK6 may have an effect on the initial right-left patterning of the embryo, which in turn influences brain asymmetry and handedness.

“This study proved the first genetic link between handedness, brain asymmetry and reading ability,” said Professor Tony Monaco, group leader. “Despite the known biological function of PCSK6, this is the first study implicating it with handedness.”

“The fact this association also seems to be apparent in people with dyslexia provides an interesting clue to explore whether there is a link between handedness and language related disorders.

If we’re left-handed are we truly left-handed? Our brain is telling us to write with our left hand, but what about everything else? There are some people who are truly left-handed – they do absolutely everything with their left. I, however, write with my left but tend to do everything else with my right hand as a right-handed person would – peeling potatoes, playing tennis, practically everything.

So am I left or right-handed? Research from the University of Western Ontario in Canada may have the answer5. Researchers asked left- and right-handers to reach towards a pair of targets with both hands at the same time and then immediately afterwards to a new, single target with the closest hand. Just before they reached for the target, a short vibratory pulse on one hand gave them a clue about where the target would appear.

On a small proportion of the trials, the pulse was given on the wrong hand meaning subjects had to restrain the reach with this incorrectly-cued hand in order to reach with the correct hand. Right-handers had more trouble dealing with the incorrect cue, making more mistakes and taking longer to successfully inhibit the reaches, almost as if the right hand was preselected.

Lefties showed no such asymmetry, suggesting they are less inherently biased to select one hand over the other. Dr Carey, who conducted the research said: “One explanation for these data is that hand choice is related to hemispheric specialisation for speech and language. Many left-handed people have “right-handed” brains which weakens the typical bias toward choosing their dominant left hand.”

Although the left might be the dominant hand, us lefties aren’t necessarily hard-wired to use it in the same way right-handers are biased towards using theirs. This may explain why the vast majority of left-handers are able to adjust to using right-handed implements, and can even find it easier.

Being left-handed can certainly be a curse – it’s hard to write in notebooks, for example, without smudging what you’ve just written – but previous generations actually thought lefties were aligned with the devil. The Latin for left is sinistra, and over time it took on the meaning of being evil or unlucky, and the word sinister has its roots here. I remember my great-grandmother telling me she used to have her knuckles rapped when she was at school in the 1920s for using her left hand because it was considered evil. However, despite this terrible treatment, she did benefit in some ways as she left school being able to write with both hands.

But being left-handed isn’t all bad – we’ve even got our own day: International Left-handers Day on 13th August. There are also many advantageous myths surrounding being left-handed – one being that we are more creative and artistic. When you look at the list of artists and musicians who were/are thought to be left-handed it’s easy to believe this might be true: Mozart, Beethoven, Picasso, Michelangelo, Da Vinci and Sir Paul McCartney and Ringo Starr.

To move anything on the left side of the body requires instruction from the right – the motor centres are more dominant in the right side of the brain in lefties, but that doesn’t necessarily mean we’re more creative.

“The big myth is that the right side of the brain is somehow a creative bulls-eye,” said David Wolman, author of A Left Hand Turn Around the World. “That’s not the case and doesn’t have anything to do with handedness. You need resources from both sides of your brain to be creative. All people use both sides of the brain.”6

Apparently, lefties are also more successful in sport. Researchers in France took an interest in the high number of lefties who were dominant in one-on-one sports like tennis, baseball and boxing2.

Their thinking is that while left-handed people would be practiced in playing or fighting right-handed people – since they make up the majority – righties won’t be as prepared to face someone who favours their left, giving lefties the upper hand.

“The fact that left-handers are less common means they have a surprise effect,” said Charlotte Faurie from the University of Montpellier in France.

So lefties might be considered some of the brightest and most gifted people, but we are prone to learning and mental difficulties, and apparently towards criminal behaviour. But for most of us, we are no more gifted or challenged than our right-handed counterparts, and there have been some truly great right-handers.

As William Hopkins, a psychologist as Emory University said: “The anomaly is left-handed people make up the extremely gifted and the extremely compromised. The rest of us make up the middle ground.”2

References 1.    Left-handedness http://en.wikipedia.org/wiki/Lefthandedness 2.    The Left-Handed Advantage, Amanda Onion http://abcnews.go.com/Technology/story?id=498707&page=1 3.    Gene for left-handedness is found http://news.bbc.co.uk/2/hi/health/6923577.stm 4.    Gene discovery supports link between handedness and language related disorders http://www.wellcome.ac.uk/News/Media-office/Press-releases/2010/WTX063319.htm 5.    What makes a Lefty: Myths and mysteries persist, Corey Binns http://www.livescience.com/655-lefty-myths-mysteries-persist.html 6.    Right-handers, but not left-handers, are biased to select their dominant hand http://www.alphagalileo.org/ViewItem.aspx?ItemId=97856&CultureCode=en 7.    Famous left-handers http://www.indiana.edu/~primate/left.html

Author Kerry Taylor-Smith is Laboratory News's staff writer. She has a degree in Natural Sciences