Handedness and the Science Behind It

I am left-handed.  My oldest brother is ambidextrous.  My father was forced to convert his dominant hand from left to right before first grade.  I have always been interested in handedness, but I never pursued it with any particular goal in mind.  That is, until a friend’s daughter, also a leftie, began having difficulties in school.  I’ve watched her grow up.  She is bright, intuitive, and curious, if a bit shy.  A mind like that should thrive in school.  So far, she has not.  Instead, she constantly comes home saying she hates school.  Hates.  That’s a very strong word for such a young child to be using.  It got me asking: what could be making her so frustrated that she didn’t want to be in school, with her friends, at all?

I started by re-evaluating my basic definition of handedness.  Most of us define our dominant hand by with which hand we write.  But that only tells a small portion of the story.  There are many fine motor skills for which we use a preferred hand: drawing, using scissors, and striking a match, just to name a few.  Handedness is defined by our overall preference for a given hand across a wide array of activities.

So, handedness is more than just writing.  That makes sense.  Humans have been around as a species much longer than we’ve been writing.  We invented tools and weapons long before we began to write.  Those inventions would have required humans to develop fine motor skills, and likely forced individuals to prefer one hand over the other.  But why is it that only about 10% of the population is left-handed?  Why is it not the case that 50% of people are left-handed and 50% right-handed?  There have been any number of hypotheses about this.  Medieval Europeans believed that being left-handed was a sign of evil.  Western cultures in the late 1800s and early 1900s believed that being left-handed was a choice made in order to buck authority.  Doctors in the mid-1900s thought that damage to the left hemisphere of the brain (which controls the right side of the body) was  the cause of left-handedness.  All of these theories define being left-handed as being lesser than being right-handed.  But modern research has shown us that there is little difference between left- and right-handed adults across many dimensions, leading us to understand that being left-handed is simply part of natural variation, like having green eyes.

This still leaves us with the ultimate question: What determines handedness?  Despite years of research, we are still far from an answer.  However, many studies using magnetic resonance imaging (MRI) techniques have found an interesting correlation.  Generally, in right-handed individuals, language is centered in the left side of the brain (which is also the hemisphere that controls the right side of the body): damage to the left hemisphere can lead to the loss of comprehension and production of speech.  The left hemisphere is also significantly larger than the right hemisphere in the brains of right-handed individuals.  Conversely, left-handed individuals are more variable in their language dominance.  Some individuals have language function centered in the right hemisphere, some have it in the left hemisphere, and some have language function spread across both hemispheres.  While the reason for this is unclear, Dr. Annett from the University of Leicester developed an insightful theory that, while simplistic, continues to provide the best explanation for the variation in handedness that I can find.  Dr. Annett proposes that handedness is a by-product of language lateralization.

In essence, Dr. Annett’s theory suggests that language lateralization is determined by two alleles at one point on the genome.  In other words, there is one dominant  version and one recessive version of the same gene and everyone has two copies.  Two dominant genes would lead the brain to develop with language lateralized to the left, and consequently causing right-handedness (although the theory does not seem to explain why the two are linked).  One dominant and one recessive gene would also lead to the brain developing with language lateralized to the left.  Finally, two recessive genes would not show a shift in brain lateralization to the left and, therefore, pure chance would determine lateralization of language function and handedness.  If the two alleles occur equally often in the human population and chance acts independently on handedness and lateralization when an individual has two recessive alleles, the theory projects that approximately 12.5% of the population would be left-handed.  This is very close to the estimate that 10 to 15 percent of the population is left-handed.

Of course, all this theorizing does not change the fact that the past ideas of the inferiority of being left-handed still permeate our society.  What does that mean for a student growing up left-handed?  For some, the constant, and often negative, comments about being left-handed can cause them to be ashamed and try to force themselves to switch hands.  Others are left feeling helpless in school.  Imagine being a young child constantly hearing his teacher tell him “It’s hard for me to show you because you use your left hand,” or “Just try to use your right hand with the scissors; we don’t have scissors for you,” or even “Don’t twist around in your desk like that; it looks like you’re cheating.” It is easy to see why he might become disenchanted with school.  After all, that is where handedness matters most for a young child.  So many fine motor skills are taught there and a teacher who is not sensitive to the differences between left- and right-handed students could instill frustrations with schooling that last well into adulthood.  Not only does this make school days difficult for the family, it can also lead to cognitive problems and later academic disadvantages for the student.

Thanks to "The Simpsons" for the quote.

There are many every day objects that are inherently designed for the right-handed individual. Even butter knives are designed with the right hand in mind.

Fortunately, it’s easy to avoid situations that might lead left-handed children to “hate” school.  It is even possible to help my friend’s daughter change her opinion of school.  An environment that minimizes tools designed only for right-handed students and intentionally incorporates tools that everyone can use (scissors that are not shaped for a specific hand, and full desks that do not have an arm rest on one side or the other like half desks) would do wonders for helping her to not feel singled out for her hand preference.  Teachers who are trained in teaching fine motor skills to students of both hand preferences are also beneficial to helping a left-handed student develop a positive attitude towards school.  Parents can make it easier on their children when they start school, too.  AS my friend already does, ensuring that the child has pens that minimize smudging can help her just as much as making sure she doesn’t have to struggle with a spiral-bound notebook.  No matter what the situation, both parents and teachers can make an effort to ensure that child’s hand-preference is never viewed in a negative light.  With the right environment, my friend’s daughter can excel in school just as much as she does at home.

Not wanting to end this post while standing on my soap box, I want to draw your attention back to the fact that handedness is not dichotomous.  People are not left-handed or right-handed.  Everyone lies somewhere on the scale of handedness where left-handed and right-handed are two extremes.  One survey, called the Edinburgh Handedness Inventory, uses a scale to determine handedness.  On this scale, -100 indicates an extremely left-handed person, -40 to 40 indicates that a person is ambidextrous, and +100 indicates extreme right-handedness.  I took the test. I scored a -88.88.  What score did you get?

11 Comments
  1. A 43 years ago
  2. Trevor 43 years ago
    • Rachelle Marie 43 years ago
  3. Margaux 43 years ago
  4. Full Article 43 years ago
    • Rachelle Marie 43 years ago
  5. north face outlet store 43 years ago
  6. Rex Gao 43 years ago
  7. aion kinah 43 years ago
  8. Albina Bernau 43 years ago

Leave a Reply

Your email address will not be published. Required fields are marked *