Scientists Look At Genetic Cause Of Left-Right Handedness
September 13, 2013

Right Or Left-Handed? It’s All In The Genes

Brett Smith for – Your Universe Online

For the ten percent of us who are left-handed, don’t feel bad about being an outsider because like Lady Gaga – you were born that way.

According to a new study in the peer-reviewed journal PLOS Genetics, handedness is determined at the embryonic stage in the womb. Study researchers said they were able to identify a network of genes that have a hand in establishing left-right asymmetry.

“The genes are involved in the biological process through which an early embryo moves on from being a round ball of cells and becomes a growing organism with an established left and right side,” said study author William Brandler, a graduate genomics student at Oxford University.

These left-right differences that first manifest at the embryonic stage eventually translate into establishing left-right asymmetry in the brain – which includes determining handedness, the study authors said.

While the exact origin of handedness still remains somewhat of a mystery, the international team of study authors was able to make their discovery through a genome-wide association analysis. Geneticists compared a wide range of genetic differences between right- and left-handed volunteers from four different population groups. The researchers said their analysis revealed that variants in the gene PCSK6 play a role to handedness determination.

Based on previous studies, the researchers noted that defects in PCSK6 and similar genes in mice can cause organs to be misplaced. For example, the heart might develop on the right side of the body and the liver on the left side. The researchers said the PCSK6 gene also appears to determine handedness at a level greater than what would occur by chance.

Brandler noted that that the study results do not completely explain the distinct handedness seen among humans.

“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.'

The researchers didn’t pose a theory as to why around 90 percent of humans are right-handed, but a popular theory says the left-hemisphere of the brain’s dominance in language functions could be a significant clue. The theory says that as language became more important to our ancestors, the left side of the brain – which controls the right side of the body – took on an increasingly larger role. If this were true, it means that the dominance of right-handedness across all populations is a side-effect of language development.

Some primate experts have theorized that language actually developed as a series of hand gestures – possibly explaining the connection between handedness and language even further. Chimpanzees and bonobos have been observed using hand gestures to communicate. These primates are also thought to be predominantly right-handed.

However, that theory is a highly controversial one, as a study published several years ago found that wild chimps are split 50-50 with respect to handedness.

The genetic study of handedness could have further reaching implications, as a study published last month found a connection between being left-handed and breast cancer in women. In the study, which included 12,000 healthy middle-aged women, researchers from University Medical Center at Utrecht in The Netherlands, found that a left-handed woman was more than twice as likely to develop pre-menopausal cancer as a right-handed woman.