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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38 replies
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  1. Paige
    Paige says:

    I believe in the twin theory because I have a twin sister and she’s right handed where as I’m left handed and I know many that are left and right handed, however non identical twins or triplets don’t seem to be left and right handed only right, I hope this helps xx ?

    • Patric
      Patric says:

      In the case of triplets; if one was left-handed and one was right-handed, then perhaps the other one would be ambidextrous….?

  2. Armen Tavy
    Armen Tavy says:

    I believe left hand is learned in infancy. A right handed mom would hip her child on her left hi and thris posses a natural instinct fir the child to use their closest hand to an object, food, toy, food, etc. The child on a left hip has their right hand at the patents backside. Right habded parents knowing there is no such thing as bring born left or right handed ususlly correct the childs outreach with their left hand while rraching, eating, drawing, by encouraging them to use their right hant, not with a NO but with putting things, objects, spoons, food, etc. nearer their right hand. Repetition is the deciding factor. I wonder how many left handed mons who hip their kids on their right hip have left handed children? I bet the odds are less.

  3. Britney
    Britney says:

    My name is Britney and I am left handed. I suffer from many impairments related to my personality which I find really relevant after learning about V.T.S. I would like to participate in research to help people understand left handed people better.

  4. google
    google says:

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