Our social world has given a notion to left and right, and we have tend to see left as things that we should not get involved in. Anyways, before we start tt rhe post, let me say that our Amino Acids are said to be left-handed while our DNA turns in a right handed helix.
That said, we can tell that the society has placed a wrong notion to left even though we have people that are left handed. Both of our hands are connected to arms, and they have the same connection but then why are they not performing the same function? You would expect that they should be used equally, or in the worse case scenario we have almost equal number of people using either sides of the hand instead of people being more right handed than left handed. In animals with preference for certain hands, wings, or hoof, the result is usually 50/50 but this is not the same with humans.
Back to societal talks on left, it has been seen that being correct is right and not being correct is left (you doubt me, so why do ballet dancers that cannot dance be said to have two left legs?), checkout words that have right as prefixes, they are words for good, for instance righteousness. The word left comes from old english word Lyft meaning weak and so on and it now looks like language is a major factor to this.
Going back to our brains. They are cross wired with the right hand being controlled by the left side of the brain and vice versa and that has made our brain symmetrical. In the 1860s when speech processes in the brain was discovered by Paul Broca known as the Broca's area is usually only located on one side and studies see that 99% of right-handers' brains have their broca's area located in the left hemisphere but this is the same with people who are left handed 70% of the time and it is only about 19% of left-handed people that process speech from the right hemisphere and 20% of left handed people uses both hemispheres of the brain to process speech. This means that speech and hand usage are not linked.
There have been theories that say that has early humans evolved, there were mutations in genes that caused much of the brain functions to be on one side allowing for specialization. The theories goes on to say that a person having two copies of the right shift mutation, it means that language and hand dominance move to the left hemisphere but the dominance and slightly shifted if one of the mutated genes is missing and if any of the mutated genes aren't carried then dominance would go to any of the hemisphere by chance. The theory says that a lack for the mutated gene for right-handedness is responsible for being left-handed.
This theory seems to do some justice to it seeing that parents pass left-handedness to their offspring where studies show that there is a 9% chance of having a left handed child from two right handed parents, 19% if one of them is left handed, and 26% if both are left handed. In 2013, a study showed that genes responsible for telling our spleens, stomach, and other organs which direction to go, either right or left during our embryonic state can be responsible for brain Asymmetry. Left handedness has also been attributed to the exposure to hormones like androgen hormones in the womb, and women who are left-handed are said to have a higher risk of breast cancer.
Wikimedia
In our world, just like 90% of the world's population, I am right-handed, 10% of people around the world are left handed while my younger brother is part of the very little percentage of people who are both handed and this is because my mom taught him how to use his right hand as a child even when his left hand was the dominant one. Studies have shown that left-handedness is more common in males than females.
Handedness is a complex trait influenced by genetics, brain structure, and possibly prenatal environment. While societal biases against the left persist, it’s clear that being left-handed is simply a variation of human development. Understanding and appreciating these differences can help dispel myths and foster a more inclusive perspective. After all, both left-handed and right-handed individuals have unique strengths and capabilities that contribute to the richness of human diversity.
Read More
https://www.scientificamerican.com/article/why-are-more-people-right/
http://web.mit.edu/7.72/restricted/levin_lecture.pdf
https://pubmed.ncbi.nlm.nih.gov/1000995/
https://journals.plos.org/plosgenetics/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2672821/
https://academic.oup.com/brain/article/123/12/2512/325690?login=false
https://www.nature.com/articles/4002053
http://www.rightleftrightwrong.com/
http://www.rightleftrightwrong.com/theories_genetic.html
https://www.nature.com/articles/6603920
https://www.ucl.ac.uk/medical-education/reprints/1983JBiosocialScience-CognitiveAbilitiesNCDS.pdf