Why Are People Left Handed?

Have you ever wondered what causes people to be born left handed?  Why are such a small percentage of society left handed, rather than it being more of a 50/50 mix? This week LeftyFretz has been trying to find out…

Through some exhaustive research (*cough*, an hour on Google!) I found out that no one really understands for sure.  Ultimately hand preference comes down to a variety of factors, partly genetic and partly environmental, but there’s no real conclusive evidence with which to give a definitive answer.

Until scientists finally crack this little conundrum we can only hypothesize at best.  Here are a few of the theories I found that attempt to explain why people are left handed.  Some are a little more far-fetched than others…

left handed people genes geneticLeft Handed Genes

Some scientists believe that left handed people simply lack the right-handed gene.   This theory has never been conclusively proven and the ‘right handed gene’ has never been located.  However, a further group of scientists have claimed to have located a specific gene which when present does show an increase in left-handedness.  Unfortunately, possession of this gene also apparently results in an increased chance of psychotic mental illness – great!

left handed evolution natural selectionEvolutionary Selection

Thomas Carlysle, a 19th century British writer suggested that left handers form such a small percentage of society as a result of some evolutionary weeding out in days gone by.  For example, a left handed warrior would hold his shield with his right hand, thereby leaving his heart (which is located more to the left) more exposed.  So the higher death rate of lefty warriors would help to justify the highly elevated number of right handed people today.

left handed prenatal traumaPrenatal Trauma/Hormonal Imbalances

Some scientists believe that babies who are exposed to traumas within the womb are more likely to exhibit left-handed tendencies.   This theory can be backed up by the fact that left handed people are more likely to develop mental illnesses, perhaps as a result of the possible brain damage incurred during the developmental period.  In more modern times it has been suggested that ultrasound scanning of the uterus can affect the development of the brain, perhaps leading to an increased chance of left handedness.

Also, studies have shown that whilst in the womb, exposure to incorrect hormonal levels can lead to an increased frequency of left handedness.  For example a recent study has shown that exposure to higher than normal levels of estrogen can increase the chances of a baby being a lefty.

Other theories suggest that exposure to high levels of testosterone can impede the development of the left side of the brain, which results in the right side becoming dominant.  As you probably know already, left handed people are generally right-brain dominant.  This theory supports the idea that there are twice as many left handed males, due to naturally higher levels of testosterone.

Research also shows that older mothers are more likely to produce left handed babies.

left handed vanishing twin theoryVanishing Twin Theory

The vanishing twins theory suggests that left handed people were originally one half of identical twin foetuses in the mother’s womb.  However the right handed foetus fails to develop very early on during the pregnancy and is reabsorbed by the mother’s body.  Although twins do have a high occurrence of left/right-handedness in the pair, this theory has been discredited by Australian scientists.

left handed physical conditioningPhysical Conditioning

People who injure or lose function of their right hand for an extended period of time can switch to a left-handed predisposition – even after the hand heals.  This usually only occurs after a period of eight months or more when the initial change to using the left handed has become the norm for the individual.

left handed through imitationImitation is the Sincerest Form of Flattery

Some younger children may try to imitate older family members or people they look up to, and end up becoming left handed themselves.  I wonder just how many 11 year old girls have taken to learning left handed guitar because of Justin Bieber?  Believe it or not, I see this on Twitter every single day!

Do you buy any of these theories?  I kinda like the dead twin thing myself, that’s some freaky stuff right there!  Or perhaps you’ve read another explanation somewhere else.  Leave your thoughts in the comments section below.

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  1. Klyde Denton
    Klyde Denton says:

    I’ve always wondered how people can be right handed ! My regret is that i really did try to play guitar right handed…for about 6 years! After all, i first learned on my father’s guitars. What a waste. After i faced the fact that it still felt unnatural (thereby causing me to suck), i switched. Much better ! )) But i would like to see an article on how many southpaws fell into the same trap.

  2. kukla my
    kukla my says:

    I don’t know how in the world I became left handed. Mama told me they first noticed it when I’d switch the spoon from the right hand to the left. All my grand parents and other relatives and Mama and Daddy were right handed; although, my first cousin also turned out left handed. My cousin and I both suffer from fainting spells and agoraphobia and other personality anomalies. I’m pretty sure I was dyslexic but over came it alone. I am also significantly right handed. If I could throw a ball, play golf or fence, I would use my right side which is much larger and stronger than my left side. I can write with either hand backwards (mirror image) or forwards. I can even write using both hands at the same time and the right hand will be the mirror image of what my left writes. My right hand can write from right to left at the same time my left hand writes from left to right and meet in the middle of the page and are the same words. I am an artist and musician and feel as if I could have excelled in math and the sciences. My brain has assigned different tasks to different hands, although I think I could reassign these tasks with which ever hand I might decide. As a child I stuttered, chewed my nails to the quick, chewed my tongue and literally bounced off the walls. I believe these days, I would have been labeled as attention deficit disorder and/or autistic. I didn’t make straight A’s in school because I never studied, but always listened in class and maintained A’s and B’s on my report card. I can remember all my friend’s birthdays, marriage dates, dates of deaths, phone numbers and most any number I need. I think most of my physiological problems stem from both sides of my brain vying for the task at hand. I labeled this condition as Incomplete dominance of the brain — kind of like having green eyes which is the incomplete dominance of having 1 blue gene and 1 brown, but neither dominated—thus green eyes.
    I never knew I could write mirror image till another left handed asked me if I could, and indeed, I could.
    Because I know the numbering system of interstates, I can travel most any where in the country, but I get lost coming home from the grocery store and I’ve lived here 30+ years.
    I wish I could unravel the secrets of these unusual gifts and voids in my brain. Until somebody figures it out, I guess I will just wonder. I hope I can get ideas from this blog.

  3. Susan
    Susan says:

    My husband and I have 3 children- all of which are left-handed. My husband is a lefty but I am right-handed. Just curious what the odds of something like that happening. And how weird for me to be the “odd” one amongst us.

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