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The Science Behind Why Some People Are Left-Handed

August 13 is International Left-handers Day, a time to take a look at all things left-handed including some research that offers a different answer to an age-old question — why are some people left-handed?

Left-handed History

The Italian word for left is sinistra. If it seems familiar that is because it shares roots with the English word ‘sinister’.

Until relatively recently left-handedness was treated with suspicion and severely frowned upon – children were regularly forced to use their right hands.

Cesare Lombroso, the 19th-century Italian described as ‘the father of criminology’, wrote a paper for North American Review in 1903 in which he preached ‘what is sure is, that criminals are more often left-handed than honest men, and lunatics are more sensitively left-sided than either of the other two.’

One of the greatest Italians ever was ambidextrous but drew and painted left-handed. Art purporting to be the work of Leonardo da Vinci can be revealed as fakes by techniques that can show they were created by a right-hander.

If you are left-handed, you find yourself in good company.

Famous lefties include Marie Curie, Albert Einstein, Mark Zuckerberg, Bill Gates, Lady Gaga, Barack Obama and George Bush Sr.

Considering that only 10 to 12 percent of the world’s population is left-handed, that is an impressive list.

Left-handed Theories

Since the 1980s scientists have been working on solving the biological riddle of what exactly determines whether we are right- or left-handed.

Despite decades of research and multiple theories as to what influences our development of right- or left-handedness, we are yet to uncover the exact science behind it.

It is widely accepted that our predilection for the right or left hand is determined while we are still in the womb, and that it starts as early as the eighth week after conception.

A 1998 study of 72 ten-week-old foetuses by Queen’s University, Belfast, found that 85 percent preferred moving their right arm more than their left. Which correlates with about 85 percent of the population being right-handed.

Some theories link hand preference to conditions during gestation, for example testosterone level as a foetus and a mother’s stress during pregnancy, while others look to genes as the answer.

Much time has been spent researching the relationship between the hemispheres of the brain and hand preference, but in 2017 scientists found a link to a different area of our body — the spinal cord.

The Latest Research

An international team of researchers, led by Sebastian Ocklenburg and Judith Schmitz from Ruhr University Bochum’s Institute of Cognitive Neuroscience, has made new discoveries.

Their research found that asymmetrical gene activity in the early stage of foetal development could be responsible for determining whether we are right- or left-handed.

The brain controls our motor functions in an area known as the motor cortex, which relays signals to our spinal cord to then relay to various parts of the body.

The Bochum-led team theorised that the spinal cord could be the key, as foetuses show signs of right- or left-handedness well before the connection between the brain and spinal cord is developed.

To prove their theory, they studied gene expression in the spinal cord of foetuses between the eighth and 12th week of development.

‘Importantly, we focused on spinal cord, not brain, tissue. Eight weeks after conception, human foetuses exhibit pronounced lateralised motor behaviour of the arms.’

They discovered a significant difference in gene expression in segments of the spinal cord responsible for controlling our arms and legs – the first time this has been proven.

Importantly, their research also points to epigenetics as playing an important role in this gene expression.

Epigenetics is what controls genes, it encompasses the chemical modifications your genes undergo from outside factors. Things like the food you eat, how much exercise you do or how much sleep you get.

Ocklenburg and Schmitz concluded that ‘our data strongly suggest a multifactorial model for the ontogenesis of hemispheric asymmetries, including both multiple genetic and epigenetic factors.’

Which in plain terms means that there are many factors which determine someone’s handedness and they include both genes and epigenetics.

The scientists’ findings seem to back up a 2006 study on sets of twins, which concluded that genes alone account for only 25 percent of the influence over right- or left-handedness, while the remaining 75 percent is down to epigenetics.

A More Left-handed World

While this study may not provide the conclusive proof we hoped for, it is noteworthy for discovering the significance of the spinal cord.

The research also opens up new possibilities to explore — in terms of gene and epigenetic research — potential keys to unlocking advances which would have much wider implications for humanity, such as a cure for cancer or even ageing.

While science continues to search for a unifying theory on what makes us righties or lefties, it is worth taking a moment to celebrate how much better our current world is for our left-handed brethren.

Unlike decades past, being a leftie does not have to be a major inconvenience anymore. These days there are all kinds of products designed specifically for lefties.

They range from the more practical, such as measuring tape and knives, to hobbyist gear like golf clubs and gaming mice.

We are creating a world more welcoming for left-handers and long may the trend continue.

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