Handedness Not Genetic: Right-Handed Versus Left-Handed Not Determined By Genes

Handedness — being right-handed or left-handed — is not controlled by genetics, say researchers from the University of Nottingham and the University College of London in a new study published in the journal Heredity.

Approximately 10 percent of the population of the United States is left-handed. That same 10 percentage holds true in most countries around the world. In other words, about 10 percent of the world population is left-handed.

Until recently, handedness was thought to be controlled by genes. Now Prof. John Armour and Dr. Angus Davison have ruled out a “strong genetic determinant” in influencing handedness.

For their study to determine if handedness was determined by genetics, the researchers compared left-handedness and right-handedness in nearly 2,000 sets of twins from the London Twin Research Unit. Even after studying the whole genome of the approximately 4,000 subjects, the researchers were unable to find a strong genetic factor in determining handedness.

As Prof. Armour, a professor of human genetics, explains:

“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.”

Within the nature-nuture debate, a combination of both genetics and environment is often the answer. Rarely does either nature or nuture solely influence human beings. The same is likely true for handedness.

As William Brandler of the MRC Functional Genomics Unit of Oxford University explains: “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.”

The researchers of the handedness study conclude that the role of genetic factors in determining handedness are most likely many but are relatively weak and subtle. Prof. Armour concludes:

“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.”

In other words, although parts of genes influence handedness in addition to the environmental factors of choice and learning, there is no right-handed or left-handed gene.