Why Are People Left Handed?

Why are some people left handed?  And why are such a small percentage of society left handed, rather than it being more of a 50/50 mix? This week I have been trying to find out…

Through some exhaustive research 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…

Why Are Some People Left Handed?

left handed people genes genetic1. Left Handed People Lack The Right Handed Gene

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 prenatal trauma2. Prenatal 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 theory3. The Vanishing 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 conditioning4. Physical 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 imitation5. Copying Left Handed Friends or Family

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!

Why Are There Fewer Left Handed People?

left handed evolution natural selection1. Evolutionary 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.

Do you buy any of these theories?  I kinda like the twin theory myself, that’s some freaky stuff right there!

Further Reading – Why Are Some People Left Handed?

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