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Left-Handedness

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Most of us know someone who uses her left hand for writing, feeding – in short – left hand dominant. While this is somewhat rare versus right-handed people like most of us, but sometimes we wonder why left-handedness occur (or why we have a dominant hand side like right-handed or left-handed).

But first let’s define handedness.

Handedness is a better (faster or more precise) performance or individual preference for use of a hand, known as the dominant hand.[1][2] This means each one of us has a dominant hand in doing skills like writing, playing an instrument, cooking, carrying a light object using one hand, feeding, etc. We can be either right-handed where our right hand is stronger or left-handed where our left hand is stronger. Some people can have both hands that are dominant i.e. can write legibly using both right and left hands – that is called ambixterity and some people can do tasks perfectly using one hand side and other tasks on the other hand side. These people have cross-handedness.

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Handedness is the hand used for activities that require a lot of practice and fine motor skills (e.g. writing) or the coordination of large muscle groups to carry out smooth actions (e.g. throwing a ball), both of which are activities employing many neurons in the brain and requiring tightly concentrated and specialized neurological wiring.[3]

Aside from the four types of handedness mentioned above, another may be considered as a type of handedness though it can be more of a disability. It is called ambilevous (or ambisinistrous) handedness[3] where people have equally poor dexterity (are equally clumsy), with both hands. This is a very rare occurrence, usually resulting from a debilitating physical condition[3] like dysgraphia

Most people (90% of the world’s population) are right-handed with approximately 60% of people being strongly right-handed (performing ALL activities with the right hand).[3] Around 10% (possibly more) of the world’s population falls into this category, although only perhaps 3% are strongly left-handed (performing ALL activities with the left hand). Cross-dominant people are slightly more common at 35% while ambidextrous people are only 1% of the world’s population.

While right-handedness may be considered the”normal” type of handedness, much wonder is made why there are left-handed people and other hand dominances.

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Image courtesy of learning4kids.net. This girl is right-handed. She uses her right hand to put the sring to the cylinder.

Why is there left-handedness?

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Image courtesy of The Independent. This is a left-handed person. He uses his left hand to write.

Different theories present a reason for hand dominance. One is is called the Division of Labor theory where since people’s speaking and handiwork require fine motor skills, its presumption is that it would be more efficient to have one brain hemisphere do both, rather than having it divided up. Since in most people, the left side of the brain controls speaking, right-handedness predominates. This theory also predicts that left-handed people have a reversed brain division of labor.[1][4]

How is this?

We know that our brains has two hemispheres, the left and right. Each hemisphere controls every activity we do. In right-handed people verbal processing takes place in the left hemisphere, whereas visuospatial processing is mostly done in the opposite hemisphere. Left-handed individuals have a heterogeneous brain organization in which their brain hemisphere is either organized in the same way as right-handers (but with the hemispheres reversed) or even such that both hemispheres are used for verbal processing.[1][4]

In short right-handed people have their motor skills done in the right hemisphere and speech at the left hemisphere while left-handed people have their brains reversed that’s why their left hand is more dominant.

Genetics is an obvious factor. Chances are if one or both your parents or someone in your immediate family or relatives is left-handed you will be left-handed also.

Penatal exposure to a drug called diethylstilbestrol (a synthetic estrogen-based fertility drug) can be a contributing factor to left-handedness in males. A 2003 study endorsed by the Centers for Disease Control determine that males with in-utero exposure to this drug are more likely to be left-handed[1][5] than those who were not exposed to it.

Presentation of the baby’s head during last trimester of pregnancy can also determine handedness. About two-thirds of fetuses present with their left occiput (back of the head) at birth. This partly explains why prematurity results in a decrease in right-handedness. Previc argues that asymmetric prenatal positioning creates asymmetric stimulation of the vestibular system, which is involved in the development of handedness.[1] People with reduced right-handedness may have either delay or anomaly in their vestibular system.[1][6] This is called prenatal vestibular asymmetry.

Ultrasound can also contribute to left-handedness. It may affect the brains of unborn children, causing higher rates of left-handedness in children whose mothers received ultrasounds during pregnancy. Research on this topic suggests there may exist a weak association between ultrasound screening (sonography used to check on the healthy development of the fetus and mother during pregnancy) and non-right-handedness.[1][7]

How common are left-handed people and how they are in everyday life?

Since right-handedness is the common hand dominance, left-handed people find it quite difficult to adjust to the right-handed world. From classroom armchairs and spiral notebooks to vehicles with steering wheels at the right side, that presents some problems if you’re left-handed. Many objects like scissors can be a struggle for left-handed folks since scissors are usually made for the right-handed.[8] Even in socialization lefties (left-handed people in short, just my coined term) have some sort of a problem like when shaking hands or giving high fives[8] especially with a right-handed person.

Left-handed people are also stereotyped. In fact, a Psychology Today article explains some of the stereotypes lefties have. Left-handed people are thought to be intelligent.[9] There are anecdotal accounts of artists and musicians tending to be left-handed, an observation given wings by the overly simplistic notion that the right-hemisphere (which controls the left hand) is the seat of creativity.[9] But as psychologist Chris McManus explains in his award-winning book Right Hand Left Hand, “although there are recurrent claims of increased creativity in left-handers, there is very little to support the idea in the scientific literature.”[9]

Left-handed people also are said to have weaker immune system and die earlier.[9] But that is only based on a statistical research of left-handed athletes who have died young.[9] Like the myth of left-handed smartness, this theory is also a myth.

This is a fact. Left-handers are less likely to be left-hemisphere dominant for language.[9] In the vast majority of the population, language function is nearly always localised to the left hemisphere.[9] Among right-handers, left-sided dominance for language approaches upwards of 95 per cent prevalence. However, among left-handed people this drops to 70 per cent, with the others either having language localised to the right hemisphere, or spread evenly across both hemispheres.[9]

In terms of income, there is no clear correlation of left-handedness to salary. One study claimed that lefties earned 10 to 15% more than their right-handed counterparts.[1][10] But a 2014 US study  published by the National Bureau of Economic Research, Harvard economist Joshua Goodman finds that left-handed people earn 10 to 12 percent less over the course of their lives than right-handed people.[1]

Left-handers are said to be common interactive sports like tennis, badminton and cricket.[1] Fencing has a lot of left-handers.[1][11] And lefties have an advantage over right-handed people in these sports. How?

Here’s a quote from Wikipedia.

The advantage to players in one-on-one sports, such as tennis, boxing, fencing or judo, is that, in a population containing perhaps 10% left-handers and 90% right-handers, the left-hander plays 90% of his or her games against right-handed opponents and is well-practiced at dealing with this asymmetry. Right-handers play 90% of their games against other right-handers. Thus, when confronted with left-handers, they are less practiced. When two left-handers compete against each other, they are both likely to be at the same level of practice as when right-handers play other right-handers. This explains why a disproportionately high number of left-handers are found in sports in which direct one-on-one action predominates.[1]

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Image courtesy of mirror.co.uk. Rafael Nadal is an example of a left-handed tennis player.

When it comes to distribution among genders, left-handedness is said to be more common in homosexuals and asexuals (people who have no sexual preference or never become attracted to any person in a romantic or sexual way).[1]

Left-handedness is also common among sexual paraphilias (people with uncommon way of sexual arousal like fetishes or sadomasochism).[1]

If this is so, why is there discrimination to left-handed people?

Because of the presentation that left-handers have, they usually face more discrimination especially in the past. They are discriminated the way autistics, slaves, and women were discriminated before. Many tools and procedures are designed to facilitate use by right-handed people, often without even realizing difficulties placed on the left-handed. John W. Santrock has written, “For centuries, left-handers have suffered unfair discrimination in a world designed for right-handers.”[1][12]

Before Industrial Revolution (when modern technology started to develop), all tools are made for right-handed people without consideration for left-handed people. Writing before was made for right-handers also using ink blot pens. When ink blot is used with left hand, stains and blotches occur[1], making the left handers more clumsy and inadequate making them prejudiced for a long time.

Languages do also refer left as wrong and right as right. Wikipedia quotes the following paragraph regarding repressing left.[1]

Moreover, apart from inconvenience, left-handed people have been considered unlucky or even malicious for their difference by the right-handed majority. In many European languages, including English, the word for the direction “right” also means “correct” or “proper”. Throughout history, being left-handed was considered negative.[1]

In French, gauche means both “left” and “awkward” or “clumsy”, while droit(e) (cognate to English direct and related to “adroit”) means both “right” and “straight”, as well as “law” and the legal sense of “right”. The name “Dexter” derives from the Latin for “right”, as does the word “dexterity” meaning manual skill. As these are all very old words, they would tend to support theories indicating that the predominance of right-handedness is an extremely old phenomenon.

That is really discriminating though. The worse is left-handedness was associated with black magic (witchcraft) hence called left-hand path.[1][13]

Discrimination still exists up to this day, but let us remember that left-handed people are just a variation of hand dominance just like variation of hair color like blonde or black.

Left-handedness Advantage

Nevertheless, being left-handed has advantages do like being good at sports stated above. Aside from this some more advantages of being left-handed are enumerated below[14]:

Lefties have a greater chance of being a genius- or having a high IQ. Researchers aren’t sure why, but those who are left handed seem to make up a disproportionately large part of those who are highly intelligent. For example, twenty percent of all Mensa members are left-handed.[14]

Left handed people adjust more easily to seeing underwater. Bizarre as it may sound, one of the benefits of being left handed is being able to adjust more easily to see the world around you when you’re underwater. While you may not need this ability very often, it could come in handy if you live by the sea or enjoy swimming.[14

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(C) Disney. Does Sebastian think of Ariel as left-handed?

Lefties are better able to multitask. One of the advantages of being left-handed is that it forces your brain to think more quickly. What this means for everyday life is that those who are lefties may find it easier to multi-task and deal with a large, sometimes unorganized stream of information.[14]

More advantages of left-handers are some of them have sharper memories, left-handed stroke patients are able to survive more than their right-handed counterparts, and also they are better in playing video games.[14] The reason is not so known but maybe because  lefties need to train both their left and right brain hemispheres, which means more brain power.

Left-handed people are also visual thinkers making ideal for an artistic occupation[14] like in arts programs.

Can left-handedness be part of neurodiversity?

Yes. Just like dyslexia and Asperger’s syndrome, left-handedness is just another brain outcome representation and absolutely not a malady that needs to be corrected. After all, left-handedness add color to human brain variety.

Reference:

  1. https://en.wikipedia.org/wiki/Handedness
  2. Holder, M.K. What does Handedness have to do with Brain Lateralization (and who cares?). Retrieved 11 August 2012.
  3. http://www.rightleftrightwrong.com/what.html
  4. Banich, Marie (1997). Neuropsychology: The Neural Bases of Mental Function.
  5. Titus-Ernstoff, L. (2003). “Psychosexual Characteristics of Men and Women Exposed Prenatally to Diethylstilbestrol”. CDC.
  6. Nonright-handedness, central nervous system and related pathology, and its lateralization: A reformulation and synthesis.
  7. Salvesen, K. Å. (1 September 2011). “Ultrasound in pregnancy and non-right handedness: meta-analysis of randomized trials”. Ultrasound in Obstetrics & Gynecology 38 (3): 267–271. doi:10.1002/uog.9055.
  8. http://www.huffingtonpost.co.uk/2014/08/13/lefthanded-problems_n_5674374.html
  9. https://www.psychologytoday.com/blog/brain-myths/201303/three-myths-and-three-facts-about-left-handers
  10. Waldfogel, Joel (August 16, 2006). “Sinister and Rich: The evidence that lefties earn more”. Slate
  11. Diana Widermann, Robert A. Barton, and Russel A. Hill. Evolutionary perspectives on sport and competition. In Roberts, S. C. (2011). Roberts, S. Craig, ed. “Applied Evolutionary Psychology”. Oxford University Press.doi:10.1093/acprof:oso/9780199586073.001.0001.ISBN 9780199586073.
  12. 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.
  13. https://en.wikipedia.org/wiki/Left-hand_path_and_right-hand_path
  14. http://www.anythinglefthanded.co.uk/being-lh/lh-info/advantages.html#sthash.I43eZA0j.dpbs