It is estimated that up to ten percent of the population is left-handed. In some cultures, the left hand is considered unclean. In some ancient cultures, the left was symbolic of evil. Children have been discouraged from using their left hands for writing as recently as the mid-twentieth century. Though there are different theories, there are still no definite answers about what causes left handedness.
While theories of the causes of left-handedness have changed over the centuries, most experts now believe that left-handedness has a biological cause. In the past, left-handedness was considered by some to be a mild birth defect. Since twins are more likely to be left-handed, some thought it was a lack of nutrients to the individual fetuses or cramped space in the womb that caused left-handedness. Some experts believed the left-handed children had been deprived of oxygen during birth.
Recent studies have concluded that there is a genetic predisposition towards left-handedness. Left-handed parents are more likely to have left-handed children than the general population. In the early twenty-first century, a study identified the gene LLRTM1 as the gene partially responsible for left-handedness. Having this gene increases the chance of left-handedness, but the causal relationship is still unclear.
Hand preference is not the only difference between left-handers and right-handers. Left-handers’ brains are slightly different in how the areas of the brain are responsible for certain functions. For a majority of left-handers, the right hemisphere of the brain control language. The opposite is true for right-handers.
The right hemisphere of the brain, which is associated with creativity, is thought to be more highly developed in left-handers while the analytical left hemisphere is dominant for right-handers. Historically, many famous artists and writers were left-handed. Michelangelo, M. C. Escher, Leonardo da Vinci, Raphael, Jimi Hendrix, H.G. Wells, and Lewis Carroll are among the famous left-handers.
Left-handers have a higher incidence rate of certain medical conditions. In addition to left-handedness, the presence of the LLRTM1 gene has also been linked to schizophrenia and psychotic mental illness. Some sources say that left-handers are more susceptible to alcoholism and Crohn’s disease than right-handers.
Left-handers have to manage in a world in which products are designed for right-handers. Though some products are made specifically for left-handers like scissors, other products that are designed for right-handers are difficult to find or not made to suit left-handers. Cameras have the buttons on the top right side. Most left-handers have adapted by using the right hand for certain tasks.