The Mystery Of Handedness
October 2, 2013

Genetics Do Not Strongly Influence Hand Dominance: Study

April Flowers for - Your Universe Online

Most of us are right handed, with only approximately ten percent of the population of the UK, and the world at large, being left handed. But why that is so remains a mystery.

Two independent studies might have given us some clues to the mystery, however.

Professor John Armour and Dr. Angus Davison from The University of Nottingham collaborated with University College London's Professor Chris McManus to rule out a "strong genetic determinant" that influences hand dominance.

The research team conducted a twin study by examining the whole genome of nearly 4,000 participants of the London Twin Research Unit to compare left and right handed participants. The researchers, whose work is published in the journal Heredity, were unable to find a strong genetic factor in determining handedness. The research team says if there were a single major genetic determination of handedness, then there should be a detectable shift between left and right handed people in the frequency of variants in that part of the genome. This was not the case.

Professor Armour, Professor of Human Genetics at The University of Nottingham, 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.”

Even though a strong genetic factor has not been found, researchers do not think that handedness is only a matter of choice or learning. The study findings suggest genetic factors are relatively weak and subtle, which has strong implications for future studies.

“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," said Armour.

In contrast, redOrbit's Brett Smith reported on the second study, which suggests handedness is determined in the embryonic stage in the womb. An international team of researchers, led by Oxford University, said they were able to identify a network of genes that are instrumental in establishing left-right asymmetry.

The findings, published in PLOS Genetics, show initial left-right differences manifest at the embryonic stage, eventually translating into left-right asymmetry in the brain. This asymmetry includes determining handedness, according to the research team.

This study agrees that the exact origin of handedness still remains largely a mystery, however, they say the basis for it lies in variants of the gene PCSK6 - which has been shown, in prior research, to cause organs to be misplaced when the gene is defective. For example, a heart might grow on the right side of the body, instead of the left.

The findings do not completely explain the distinct handedness seen among humans, the researchers note.

“As with all aspects of human behavior, nature and nurture go hand-in-hand,” he said. “The development of handedness derives from a mixture of genes, environment, and cultural pressure to conform to right-handedness," said William Brandler, a graduate genomics student at Oxford University.