If You Are Left-Handed Like Me You Will Want to Read This

September 14, 2019 – Approximately 10 to 13% of the human species are left-hand dominant. My family bucked the trend with three of the four of us being left-handed even though neither parent wrote with their left. In looking at my father’s writing I am almost certain that he was of a generation of left-handed people who were forced right in school back in the 1920s. And if you didn’t know this, if you are a leftie (not political) then you share that characteristic with the last two Democratic presidents, Barack Obama, and Bill Clinton. Although both were lefties, neither could be described as politically on the left.

What causes one hand to be dominant in a species?

What does it say about our brains when we use our left-hand over our right?

A recent study of 500,000 people’s genetic data done by researchers at the University of Oxford revealed four areas of our genome that govern left-handedness. Three of these were associated with brain development and language proficiency. Akira Wiberg, a researcher at Oxford and one of the lead authors of the study noted that people who are left-handed appear to have a different pattern of brain communication between the left and right brain hemispheres.

In Brain: A Journal of Neurology, Wiberg and her research colleagues describe our uniquely human character trait, a predominance of right-handedness. This is uncharacteristic in other animal species were dominant handedness is evenly distributed between left and right. In our nearest primate relatives, the numbers do not weigh heavily to the right.

So what could be the explanation for this unique skewed human characteristic?

Some anthropologists believe that the use of stone tools made us right-hand dominant. The left hemisphere of the human brain controls motor coordination critical to developing stone tools. Pointing to dental records of European Neanderthals, researchers see in the fossil record evidence of right-slanted striations on the front side of teeth. They hypothesize that the striations came from gripping material with the teeth while striking an object being worked with the right hand. The same evidence appears in earlier Homo habilis fossils. Hence, anthropologists believe marks like these could only come from working with tools held in the right hand. Subsequently, a combination of genomic inheritance and learned behaviour skewed human populations to become right-hand dominant.

A more disturbing aspect of the Oxford research links the four areas of the genome associated with left-handedness with several neurodevelopmental disorders including schizophrenia.

The study found that:

• left-handedness is influenced by genetics, running in families like mine. In identical twins left-handedness has an estimated heritability of 25%.
• left-handers’ brains showed a stronger connectivity between the right (Broca’s area) of the brain with the left hemisphere influencing language development.
• those who were ambidextrous exhibited a fifth area of the genome associated with this capability.
• the genomic consistencies associated negatively impacted the occurrence of Parkinson’s Disease in those who were left-handed
• other neurodegenerative conditions such as anorexia nervosa, auditory hallucinations, and bipolar disorder, however, were more likely in left-handers.

The most interesting aspect of this dominant-hand study is how dominant-handedness and verbal skills in language are linked giving left-handers a cognitive advantage. Being a left-hander, all I can say is “I knew it! Now, could someone help me open this can of tuna with this right-handed can opener?”