Why Are Some People Left-Handed?

Left-handed people have been ostracized throughout history. They have been hailed as the spawns of the devil and even burned on stakes. They have also suffered under the tyranny of left-to-right scripts, and worst of all, they always had to use scissors designed for right-handed people!

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The superstition against sinistrality, better known as left-handedness, is so entrenched in our culture that even the word ‘right’ means good or pure. On the other hand (see what I did there?), sinistrality comes from the Latin word sinistra meaning ‘left’, which is also the origin of the word ‘sinister’.

Despite the apparent dislike of this minority, there is a 10% chance of you being born left-handed. This percentage within the population has remained the same for the past 500,000 years!

If being left-handed has always been such a genetic disadvantage, then why does a healthy and stable population of lefties still exist?

What is it that actually makes a person left-handed?

Nature

Scientists have several theories that might explain why some people are lefties. Some use neurological theories, such as Brain Laterality, to justify left-handedness, while others suggest genetic reasons. Here, for the sake of brevity, I will only indulge in the genetic understanding of “handedness”.

As opposed to what some people believe, you don’t choose to be either right-handed or left-handed person. Handedness can actually be determined in the prenatal stage by the position of the fetus in the womb!

Experts have found a definite correlation between genetics and handedness through the study of twins. Identical twins can have different dominant hands, just as normal siblings can. However, the handedness of the parents seem to play a huge role in determining their handedness in a surprisingly consistent ratio.

If both of your parents are right-handed, then the chances of you being born a left-handed person is only 10%. If your dad is a lefty and your mother is not, then that probability spikes up to 17%. If your mother is a lefty and your father isn’t, then there is a 22% chance of you being born a lefty. If both your parents are left-handed, congratulations!… you have a 25% chance of being left-handed just like Mom and Dad!

Despite numerous attempts, geneticists have failed to isolate the genes that clearly determine handedness. The reigning belief is that this is because there is not one, but many genes that contribute to making one of your hands more dominant than the other. However, some believe that genetics may not be the only answer.

You see, apes also display handedness, but unlike humans, there is a 50-50 chance for an ape to be either left-handed or right-handed. With that observation, we can assume that apes don’t really have a genetic preference for one particular hand. However, in the case of human beings, the right hand wins 9 out of 10 times.

Why is it that this small population of lefties continue to persist in our population? If genes were solely responsible, then natural selection would have ideally gotten rid of them by now. To explain the consistent ratio between right-handed and left-handed people, perhaps we need to step beyond mere genetics.

Nurture

Another theory suggests that the above ratio is representative of the competitive and cooperative pressures in human society.

The benefits of left-handedness are seen in competitive sports. 50% of baseball players are left-handed. This is because as a player, you anticipate right-handed opponents 9 out of 10 times, even if you are a left-handed person. However, if your opponent is a left-handed person, you are thrown off balance. Similarly, being left-handed would obviously be a major advantage if you were fighting another human being for survival.

Brian Lara, one of the best cricketers in the world, is a lefty. Source: Wikipedia

Brian Lara, one of the best cricketers in the world, is a lefty.
Source: Wikipedia

This is called negative frequency-dependent selection. This states that the rarer a trait is, the more valuable it is for an organism’s survival. What this means is that a certain group with an advantage over the others tends to grow until that advantage disappears altogether. If humans were solitary competing creatures, natural selection would tend to increase the number of lefties in our population. That number would continue to grow until the trait was no longer rare, and thus no longer advantageous.

However, humans don’t live in a purely competitive world. We live as complex social animals and are dependent on each other for survival. The cooperative pressure of fitting into the society is stronger than the competitive pressure of being better than your peers.


Several scientists believe that environment must have played a large part in creating handedness. A phenomenon called tool-sharing contributes to this school of thought. The tools that were developed in ancient society were designed for the majority of people, i.e. right-handed people. The left-handed people simply couldn’t keep up with the technology! They were also more prone to losing battles against the wilderness because of their ineptitude at using right-handed weapons. Sadly, they eventually diminished from the gene pool, leading to a dominant preference towards right-handedness.

The scope of tool-sharing soon increased, continuing to exclusively cater to the right-handed population. Even when writing was discovered, the majority of languages chose to use a left-to-right script. Such scripts are written easily with the right hand, but they are not as easy with the left one. Even I, as a left-handed person, learned to write with my right hand as a child due to how dirty my hands would get while writing with a pencil. Therefore, it has become impractical to have a large number of lefties in the population, and we continue to be systematically weeded out through natural selection.

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In a purely cooperative world, there would be absolutely no left-handed people.

Then again, we don’t live in a purely cooperative world either, so a healthy number of left-handed people continue to elude the evolutionary filter and are born against the odds.

Basically, if we consider the ratio of left-handed people to right-handed people, it gives us some fascinating insights into human history. 

All Lefties be like..

All lefties be like..

The existence of a small but stable minority of left-handed people suggests an equilibrium that comes from both cooperative and competitive effects playing out simultaneously over time. The understanding of human interaction is, quite literally, in our hands!

References:

  1. Handedness – Wikipedia
  2. Left-Handed People More Likely To Have Psychotic Disorders Such As Achizophrenia – Yale News
  3. Why Are Some People Left-Handed? – Smithsonian.com
  4. TedEd
The short URL of the present article is: http://sciabc.us/XwkXp
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About the Author:

Vaishnavi has a bachelor’s degree in Sociology/Anthropology from St. Xavier’s College, Mumbai (India) and is currently pursuing a Master’s Degree in Global Studies (whatever that is) from Humboldt University, Berlin (Germany). She loves to read and to sing, especially to avoid awkward situations. She claims she has learned a lot through traveling but she still ends up pulling a door marked ‘Push’, so the jury is still out on that one.

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