Why call a valued assistant a ‘right-hand man’? Why does an awkward dancer have ‘two left feet’? And why, in times gone by, were left-handers thought to be possessed by the devil? Throughout the ages left-handers have been stigmatised and persecuted. But it turns out ‘handedness’ is determined before you even leave the womb.
Are you a southpaw?
Statistics tell me only about 10% of you reading this are left-handed. In contrast, chimpanzees show a 50:50 split in preferred hand. This 90:10 ratio is true in every human population in the world and is thought to have been true throughout human history.
Does this rarity explain the persecution? The very name tells us the negative perception of left-handers has a long history. ‘Left’ comes from the Old English ‘lyft’ meaning weak or broken and ‘sinister’ in Latin means both left and bad, or unlucky. In contrast the Latin for right is ‘dexter’, which gave us the word ‘dexterous’, meaning skillful.
Are more left-handers criminals?
Back in 1903, Cesare Lombroso, the father of modern criminology, announced left-handers were more than three times as common in criminal populations than in the rest of the population.
Left-handedness… may contribute to form one of the worst characters among the human species.Cesare Lombroso
In 1977, psychologist Theodore Blau claimed left-handed children were overrepresented among academically and behaviorally-challenged children.
Another psychologist, Stanley Cohen, argued left-handers die younger than their right-handed counterparts. On closer inspection it turned out simply that the older a person was, the more likely they had been forced to override their natural left-handed preference and learn to write with their right hand. We know today only 1% of Chinese students are left-handed while the proportion in the general population is 10%.
The truth about left-handers
We know people with psychotic disorders like schizophrenia are more likely to be left-handed. We also know if you are left-handed, you are twice as likely to be male. And we find a higher proportion of left-handers among architecture, art and music students than among science students.
There are also many famous left-handers: Plato, Charles Darwin, Bill Gates, Oprah Winfrey, Jimi Hendrix, Picasso, Leonardo da Vinci and Ned Flanders to name but a few. And five out of the last seven US presidents have been left-handed. People argue that left-handers are more introverted, creative and intelligent.
Five of the past seven US presidents, including Barack Obama, have been left-handed. Image credit: Pete Souza (public domain) via Wikimedia Commons.
Where does hand preference come from?
Research published last year showed hand preference begins in the womb and scientists have identified the network of genes responsible. These genes establish left-right differences in the brain, which in turn influences which hand is favoured while an embryo develops. These are also the genes that ensure our internal organs are correctly positioned in our bodies – for example, our heart and stomach on the left and our liver on the right.
So left-handedness isn’t a character flaw, but simply an outcome of genetic variation. And in fact, being left-handed may deliver some important advantages.
The right brain knows what the left hand is doing
Information collected on the right side of the body (for example the right ear and eye) goes to the left hemisphere of the brain for processing. At the same time, information from the left side goes to the right brain. Right-handers tend to do most of their processing of language and speech in the left side of the brain while the right side of the brain is responsible for emotions.
But left-handers don’t tend to divide these tasks so clearly between the two hemispheres. Left-handers are more likely to process language using both sides of the brain. And tests designed to look at the speed of information flow between the two halves of the brain have found that in left-handers, the two halves of the brain are better connected.
This greater connectivity means left-handers are at an advantage when it comes to processing and responding to lots of information arriving simultaneously or in quick succession (think being a pilot, or perhaps a gamer!)
Left-handers are also better at divergent thinking than right-handers. This may be because in the process of more information passing between the two brain hemispheres, there is more opportunity for novel ideas.
So rather than being sinister or unlucky, it seems left-handers may indeed be more creative. Which raises the question – why hasn’t left-handedness evolved to be more common?
Espresso Science 
