Researchers at the University of Oxford have identified a gene that increases the likelihood of its carrier being left-handed.
The gene plays a role in developing brain symmetry and is also associated with an elevated risk of developing mental illnesses such as schizophrenia.
Called LRRTM1, the gene is involved in allocating functions such as speech and language processing to different areas of the brain. Asymmetry in the brain is normal: ordinarily the left side of the brain controls language and speech, while the right deals with emotion. In left-handers this is reversed.
Unusual balances of brain function are not just associated with handedness, though, they are also linked to various psychotic disorders including schizophrenia.
But despite their findings, the researchers say left-handed people, that is one in ten of us, should not be alarmed.
Study leader Dr Clyde Francks, of the Wellcome Trust Centre for Human Genetics, said: "People really should not be concerned by this result. There are many factors which make individuals more likely to develop schizophrenia and the vast majority of left-handers will never develop a problem. We don't yet know the precise role of this gene."
Asymmetry in the brain may also have been an important evolutionary step: apes have much more symmetrical brain function than do humans, for instance, and show no preference for using either left or right hands.
The research is published in the journal Molecular Psychiatry. ®