International Left-handers Day is an annual event celebrated on August 13. Left-handers are well-organized with Facebook groups, a presence on Twitter and international clubs publishing newsletters and selling implements and tools designed for left-handers. One interesting fact is that rates of left-handedness vary depending on the region of the world. This fact presents a problem when I am asked about the overall worldwide rate of left-handedness during media interviews. I usually give an estimate of 10% which unfortunately hides the reality that rates of left-handedness vary by as much as 6% across different geographical regions. In my book Laterality: Exploring the enigma of left-handedness, I present data from studies published over the past 55 years reporting rates of left-handedness in different countries. The highest rates of left-handedness, 10%, occur in North America, Australia, New Zealand and western Europe. The lowest rates, 4 to 6%, are in Asia, Africa and South America.

Several theories attempt to explain the geographical variation in the prevalence of left-handedness. Researchers who favor a genetic explanation for left-handedness argue that differences in the gene pool among regional groups around the world account for the varying rates of left-handedness. Recent studies indicate that the genetics of handedness are complex. As many as 40 genetic sites may contribute to the development of handedness side. Despite this complexity, it is theoretically possible that populations in some regions of the world have a genetic endowment toward left-handedness that populations in other regions do not possess.

A second approach claims that differences in attitudes toward the use of the left hand explain cross-cultural differences in rates of left-handedness. Countries with higher rates of left-handedness are societies that tolerate left-handedness, do not punish left-hand use and do not pressure left-handers to convert to right-handedness. The low rates of left-handedness in Africa are explained by the close ties to Arabic culture and Islam in many African countries. Muslims must handle food and write with the right hand. Using the left hand in public and greeting another person with the left hand is a sign of disrespect. Surveys conducted in Africa find that many people consider the left hand to be dirty. Use the right hand for clean activities, such as writing and eating, and reserve the left hand for unclean toilet activities. Such attitudes foster converting left-handers to right-hand use resulting in low rates of left-handedness.

A third view emphasizes overall cultural climate in different countries rather than focusing on specific handedness conversion pressures. One researcher classified countries with a numeric score called the Power Distance Index (PDI). Countries with high PDI scores value obedience and conformity while those with low PDI ratings emphasize independence. Countries with high PDI scores are called formal cultures while those with low PDI ratings are non-formal. Formal cultures promote conformity to the majority pattern, right-handedness, while non-formal cultures allow for the individual expression of handedness type. PDI ratings roughly predict the variation in rates of left-handedness around the world. Sixty-eight percent (68%) of the countries with formal cultures according to the PDI are in Asia, Africa and South America, regions of the world with the lowest rates of left-handedness.

Left-handers around the world are finding each other through social media. This is especially valuable for left-handers who live in countries where left-handedness is not valued and may be penalized. It is important for these left-handers to discover a community of acceptance among left-handers in other parts of the globe.  HAPPY LEFT-HANDERS DAY TO ALL!