It was once believed that left-handedness was a curse and that all lefties had been marked out by the devil to do his bidding on Earth. Fortunately, we now have actual science, allowing a team of researchers to identify the genes associated with left-handedness. As it turns out, these genes are also strongly implicated with structuring the brain, and are even associated with conditions like schizophrenia and dementia.
Writing in the journal Brain, the study authors explain that previous research has shown that identical twins are more likely to display the same handedness than non-identical twins, suggesting that handedness is largely genetic.
To try to identify the specific genes involved, the researchers examined the genomes of nearly 400,000 people in the UK, 38,332 of whom were left-handed.
Analysis showed that four distinct genetic regions appear to be largely responsible for left-handedness, and that three of these also code for the formation of proteins that make up the scaffolding – or cytoskeleton – of brain cells.
Compared to right-handers, therefore, lefties tend to display differences in the structure of certain brain regions, particularly those that deal with language.
Commenting on this finding, study co-author Akira Wiberg explained that "in left-handed participants, the language areas of the left and right sides of the brain communicate with each other in a more coordinated way. This raises the intriguing possibility for future research that left-handers might have an advantage when it comes to performing verbal tasks, but it must be remembered that these differences were only seen as averages over very large numbers of people and not all left-handers will be similar."
When looking closer at the genes involved, it appears that they all also have a hand in psychiatric disorders and cognitive decline. For instance, the gene that is most strongly connected to left-handedness – called rs199512 – is also known to play a role in Parkinson’s disease and certain mental health traits such as neuroticism.
On top of that, the communication tracts that coordinate language in the brain have consistently been shown to be associated with schizophrenia and auditory hallucinations.
However, the researchers also point out that these genes only cause mental health problems in a tiny number of people, so being a leftie should not be considered a major risk factor for any of these conditions. Realistically, the only thing that left-handers really have to worry about is smudging their handwriting.
And for anyone hanging on to medieval superstitions, this research should put an end to any fears regarding a Satanic left-handed army.