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While growing up in a semi-urban area somewhere in the Southwestern part of Nigeria - among the Yoruba speaking tribe, several unusual beliefs were held or practiced. Looking back now, some of those beliefs seem weird and have no scientific basis while many of them can be explained using relevant scientific evidence. One of those practices was to introduce powdery substances into water meant to be boiled in order to hasten its boiling. Of course, the explanation that impurities lower the boiling point of water later cleared the air and effectively proved the practice right. 

Another of those beliefs was the opinion that left-handed individuals are usually academically smarter than their right-handed counterparts. Similarly, when it comes to the game of soccer, the belief then was that left-legged players are generally more skillful than right-legged players. Interestingly, using the left hand for some actions is generally frown at in the culture. For example, Using a left hand to deliver an object to an elderly person is considered disrespectful, and such action often attracts correction. You will be asked to return the object to your right hand before delivery. 

# Brain lateralization and left/right-handedness
The neural functions or cognitive processes of the brain in humans are usually compartmentalized either to the left hemisphere or the right hemisphere of the organ. Both brain hemispheres are like mirror images of each other and are linked together by a structure known as the corpus callosum - a structure that enables both hemispheres to communicate with each other.<sup>[1](https://en.wikipedia.org/wiki/Lateralization_of_brain_function)</sup> Aside from being the coordinating center of some cognitive functions, the right hemisphere of the brain controls the left-hand side of the body while the left hemisphere coordinates the right-hand side of the body. However, being left/right-handed has been proven to be much more than about the right/left brain hemisphere.

<center>https://upload.wikimedia.org/wikipedia/commons/thumb/7/78/Brain_Lateralization.svg/1280px-Brain_Lateralization.svg.png</center>
<center><sup>[Brain lateralization By Chickensaresocute - Own work, CC BY-SA 3.0](https://commons.wikimedia.org/w/index.php?curid=26371690)</sup></center>


Scientists have found that being left or right-handed has a lot to do with a combination of genetics and environment, rather than brain lateralization. According to research, alleles D and C make up the gene responsible for left/right-handedness. The definition of alleles as alternate forms of genes is modified in this case because while D controls right-handedness, allele C can control left or right-handedness equally. Whichever of the hands that will be dominant in the case of individuals with the C allele will largely depend on the environment - nurture.

Looking at the fact that a gene is made up of two alleles, it thus means that DD and DC individuals will be right-handed while individuals with CC genotypes have an equal chance of being right-handed or left-handed subject to cultural snd societal upbringings. According to researchers, the D allele has a higher frequency of occurrence in the human gene pool when compared to the C allele. This ipso-facto explains the fact that there are more right-handed than left-handed humans in nature. In a culture where using the left hand is frowned at, the frequency of right-handed people will even be more because the chance of CC individuals being pressured into using the right-hand will be more.<sup>[2](https://www.scientificamerican.com/article/what-causes-some-people-t/)</sup>

# Right/left-handedness and cognitive ability
Like I pointed out earlier, even though using the left hand to perform some tasks is generally frown at in our culture here, the belief is that left-handed individuals have higher cognitive abilities than their right-handed counterparts. This belief, however, has been experimentally tested by several researchers.

<center>https://p0.pxfuel.com/preview/855/686/447/laptop-mobile-hand-notebook.jpg</center>
<center><sup>credit: [pxfuel](https://www.pxfuel.com/en/free-photo-jrzsi)</sup></center>

Jasem and his colleagues in 2016 are among the researchers that have conducted an investigation to assess the relationship between being right/left-handed and cognitive ability. They selected an equal number of right and left-handed individuals within the same age bracket and assessed their cognitive abilities using relevant metrics. While left-handed individuals were found to have better simple reaction time, right-handed individuals had superior visuospatial abilities. Details about the experiment can be found [here](https://www.hindawi.com/journals/neuroscience/2016/6740267/).

Researchers like [Benbow (1986)](https://www.sciencedirect.com/science/article/abs/pii/0028393286900114) and [Annett and Manning (1990)](https://www.sciencedirect.com/science/article/abs/pii/S0010945282800531) had earlier reported a positive correlation between left-handedness and cognitive skills relating to mathematics, but this notion was dispelled by the report of  [Johnston et al](https://rss.onlinelibrary.wiley.com/doi/abs/10.1111/j.1467-985X.2012.01074.x) in 2013. Nicholls and his coworkers also investigated the claim that hand preference has effects on an individual's general cognitive abilities but while they admitted there could be a form of correlation, they could not arrive at a concrete conclusion and recommended further research to be done on a large scale. However, when it comes to general development in children, hand preference - left-handedness and mix-handedness to be specific - has been reported to be less advantageous according to the research of  [Johnston et al (2009)](https://www.jstor.org/stable/20616464?seq=1).

# Too Long:Didn't read?
Being left or right-handed is often associated with the cognitive abilities of individuals but research has shown that this is not entirely true, with some researchers reporting mixed results. While the neural and cognitive functions of the brain are lateralized, lateralization has no bearing on being left or right-handed. Instead, hand preference is controlled by a special gene with D and C alleles. The D alleles codes for right-handedness while the C allele codes of either of right/left-handedness depending on cultural or societal influence. 

Thank you all for reading.


# Resources
* [Brain Hemispheres](https://courses.lumenlearning.com/waymaker-psychology/chapter/the-brain-and-spinal-cord/)
* [Lateralization of brain function](https://en.wikipedia.org/wiki/Lateralization_of_brain_function)
* [What causes some people to be left-handed, and why are fewer people left-handed than right-handed?](https://www.scientificamerican.com/article/what-causes-some-people-t/)
* Nicholls, Michael (Mike) & Chapman, Heidi & Loetscher, Tobias & Grimshaw, Gina. (2010). The relationship between hand preference, hand performance, and general cognitive ability. Journal of the International Neuropsychological Society: JINS. 16. 585-92. 10.1017/S1355617710000184. 
* Johnston, D., Nicholls, M., Shah, M., & Shields, M. (2009). Nature's Experiment? Handedness and Early Childhood Development. Demography, 46(2), 281-301. Retrieved August 13, 2020, from www.jstor.org/stable/20616464

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