There is a long-standing joke that says: Since the left side of the brain controls the right side of the body, and the right side of the brain controls the left side of the body, only people who are left-handed are in their right minds! That seems simplistic, and it certainly gives comfort to left-handed people who have suffered abuse their entire lives for being “abnormal†and thought of as being “bad luck,†but it isn’t true.
When discussing handedness (also known as chirality or laterality) scientists refer to the hand a person chooses to use for their fine motor skills, like holding a writing instrument or eating utensils. Some people are more comfortable using their right hand, some their left hand, some switch hit and use each hand at different times for different functions (mixed-handedness), while still others are equally skilled using either (ambidextrous).
Approximately 3%-4% of the world’s population is solely left-handed, 25%-33% are mixed, and 60%-70% are consistently right-handed. Truly ambidextrous people are rare. These statistics are surprising because most people believe others are either left or right-handed, and only a few are able to function well using both hands.
Scientists have been studying hand dominance for over 150 years and are still stumped as to the correlation between handedness and brain lateralization. They still find that some people process language skills on the left side, others on the right, and there is no guarantee that left-handed people only utilize the right hemisphere of their brain to process language, and that right-handed people only process languages on their left side (a majority of left-handers seem to have a left-hemispheric brain specialization for language abilities). It has been a baffling puzzle that may never be understood. It also is not true that handedness is inherited, but parents who are both left-handed do have a better chance of having a left-handed offspring.
Left-handed people have learned to adapt to tools and facilities that are designed by, and for, right-handed people (left-handed people would design them to either fit left-hand dominants or for the convenience of both). For this reason, many scientists believe those with dominance of the left hand are able to utilize more of their brain surface than right-handed people.
There are only theories as to why the majority of people are right-hand dominant. The statistics are universal among most cultures, although primitive societies seem to have a higher percentage of left-hand dominant people. The most recent views are that handedness is not a preference for one hand, but that two hands actually work together in subtle ways, such as one hand holding the paper while the other holds the pen.
There is a theory that is most commonly accepted, believing that since both speaking and handiwork require fine motor skills, it would be more efficient to have one hemisphere of the brain do both, so man has adapted the right-hand as primary is most expedient.
Some studies have shown that left-handed people seem to have better visual-spatial skills and the ability to imagine spatial layouts. In one study of more than 100,000 students taking the SAT (Standard Aptitude Test) 20% of the top-scoring students were left-handed. That is twice the percentage of the population as a whole. Other studies found no difference in mental performance.
So, although left-handed people have been discriminated against for centuries because they were misunderstood, there is no conclusive research to define the reason why one person prefers one hand to the other, and nothing to indicate that one side of the brain is more dominant for the other.
This is Ron White, and I am a memory-training expert, memory keynote speaker, and two-time USA Memory Champion.
Sources:
Wikipedia – Handedness: http://en.wikipedia.org/wiki/Handedness
Santrock, John W.(2008). Motor, Sensory, and Perceptual Development. Mike Ryan [Ed.], A Topical Approach to Life-Span Development(pgs.172-205). Boston, MA: McGraw-Hill Higher Education.
Indiana University – Handedness and Brain Lateralization: http://www.indiana.edu/~primate/brain.html
The Journal for Neuropsychiatry and Clinical Neuroscience – Handedness and Cerebral Dominance: http://neuro.psychiatryonline.org/cgi/content/full/10/4/459