Scientists have found the first genetic instructions hardwired into human DNA that are linked to being left-handed.
The instructions also seem to be heavily involved in the structure and function of the brain – particularly the parts involved in language.
The team at the University of Oxford say left-handed people may have better verbal skills as a result.
But many mysteries remain regarding the connection between brain development and the dominant hand. About one in 10 people is left handed.
Studies on twins have already revealed genetics – the DNA inherited from parents – has some role to play.
However, the specifics are only now being revealed.
The research team turned to the UK Biobank – a study of about 400,000 people who had the full sequence of their genetic code, their DNA, recorded. Just over 38,000 were left-handed
And the scientists played a giant game of spot-the-difference to find the regions of their DNA that influenced left-handedness.
The study, published in the journal Brain, found four hotspots.
“It tells us for the first time that handedness has a genetic component,” Prof Gwenaëlle Douaud, one of the researchers, told BBC News.
Scans of participants in the UK Biobank project showed the cytoskeleton was changing the structure of the white matter in the brain.
“For the first time in humans, we have been able to establish that these handedness-associated cytoskeletal differences are actually visible in the brain,” Prof Douaud, who is herself left handed, said.
In the left-handed participants, the two halves of the brain – the left and right hemispheres – were better connected and more co-ordinated in regions involved in language.
The researchers speculate left-handed people may have better verbal skills, although they do not have the data from this study to prove it.
The study also showed slightly higher risks of schizophrenia, and slightly lower risks of Parkinson’s disease, in left-handed people.