Left or right? It’s not genetic

It is often assumed that handedness is inherited but a new study rules out a strong genetic factor in determining what hand a person writes with.

Researchers from the University of Nottingham conducted a twin study, examining the whole genome of 3940 twins from the London Twin Research Unit to compare left and right handed participants.

The study – published in Heredity – failed to find a strong genetic factor in determining handedness. If there was a single major genetic determination of handedness, there should be a detectable shift between left and right handed people in the frequency of variants in that part of the genome.

“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,” said Professor John Armour, Professor of Human Genetics. “A survey that compared the whole-genome genotypes for right and left handed people should leave such a gene nowhere to hide.”

Despite the lack of a strong genetic factor, it is still widely believed that handedness is not only a matter of choice or learning. This study – carried out with Dr Angus Davison from Nottingham, and Professor Chris McManus from UCL – suggests genetic factors must be relatively weak and subtle, which could form the basis for future work.

“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,” said Armour. “As a consequence, even if these genes are identified in the future, it is very unlikely that handedness could usefully be predicted by analysis of human DNA.”