Over 10% of the US population is left-handed - and this percentage seems to be about the same in most countries around the world. Though no one knows exactly what makes someone left- or right-handed, it is tempting to say it is genetic. But new research from the UK challenges this belief.
The University of Nottingham's Prof. John Armour and Dr. Angus Davison, and University College of London's Prof. Chris McManus, have ruled out a "strong genetic determinant" in influencing handedness.
The study, published in the journal Heredity compared left- and right-handedness in nearly 2,000 sets of twins from the London Twin Research Unit.
The researchers studied the whole genome of approximately 4,000 subjects but were unable to find a strong genetic factor in determining handedness.
If genetics played a dominant role in determining left- or right-handedness, scientists would expect to see a difference in the part of the genome that influences this. But the research did not back this up.
This finding challenges the results of a previous study by the MRC Functional Genomics Unit Oxford University, which claimed to have found significantly strong association with right- or left-handedness in the gene PCSK6.
'Nowhere to hide'
Prof. Armour, the University of Nottingham's professor of human genetics, said:
"There should be a detectable shift between right- and left-handed people because modern methods for typing genetic variation cover nearly all of the genome. A survey that compared the whole-genome genotypes for right- and left-handed people should leave such a gene nowhere to hide."
But the professors are not deterred by the lack of evidence for a strong genetic factor, concluding that these factors must be relatively subtle or weak, rather than being a matter of choice or learning.
William Brandler, of Oxford University's MRC Functional Genomics Unit and first author of the earlier study that found a genetic association, warned previously that their results did not completely explain the variation of left- and right-handedness within the human population:
"As with all aspects of human behavior, nature and nurture go hand-in-hand. The development of handedness derives from a mixture of genes, environment, and cultural pressure to conform to right-handedness."And, as Prof. Armour emphasized, the results of this latest study present opportunities for further research.
"It is likely that there are many relatively weak genetic factors in handedness, rather than any strong factors, and much bigger studies than our own will be needed to identify such genes unambiguously. As a consequence, even if these genes are identified in the future, it is very unlikely that handedness could be usefully predicted by analysis of human DNA."