About 90% of people are right-handed. This must be rooted in the fact that the heart is on the left side of the body, and right handedness must have given rise to the marked tendency of the language areas of the brain to be located within the left hemisphere.
This interesting combination must have been acquired with certain universality even among the ancestors of mankind and, by nature or nurture, passed on to humans living today.
1. Heart Exposed on Left Side
Mankind is said to have adopted bipedalism in the African rift valley, in a departure from a lifestyle dependent on trees for food, shelter and protection, much in the way many primates still do. These forefathers of mankind would stand up and walk and run in the open areas, in the hope of finding more food.
In a standing position, the heart is located near the center of the body, with the base pointing inwards, close to the esophagus, and the apex (containing the ventricles that contract for pumping blood into the arteries) pointing leftwards and coming closer to the surface of the body.
Because of this configuration, humans must have felt early on that, if the right hand is used for strenuous activities that require physical strength, this was less taxing on the heart than the left hand, because the heart is less exposed from the right side of the body.
2. Use of Fire
In this context, the use of fire must have served as a definitive factor that prompted humans to use the right-hand, as using the left hand when handling fire must have caused problems; the apex of the heart, exposed on the left side of the body, would be closer to the heat, and the rhythm of the heart would be adversely affected, making it necessary to take a break frequently.
They would have preferred to use the right hand where possible, as this would shelter the heart from high temperatures.
(Anyone interested should try ironing clothes with the left hand, to understand how rapidly heat can climb up your body and tire you out; using the right hand makes it much easier to handle a hot iron.)
So this must be how humankind took a definite preference for right-handedness, at first for cooking food and then for creating earthenware and pottery and, eventually, for making tools out of metals such as gold, silver, bronze and iron. In fact, this may account for the higher incidence of right-handedness among females, as they may have spent longer hours in the kitchen, handling fire on a more daily basis than the males.
Although primitive weapons including swords and daggers, lances and clubs may give off the first-hand impression that, since they were more or less symmetric in shape, they should have been handled equally well by both righties and lefties, on second thought, this may not be so true.
This is because warriors needed to protect certain parts of the body as a matter of high priority during hand- to- hand combat, and this included the heart, not to speak of the head.
This meant it was better to handle swords, lances etc. with the right hand, so as to keep the enemy at a distance from the heart; in fact, the martial arts including fencing must have been developed on the understanding of such particular vulnerabilities, and come to recommend the use of the right hand where possible. The left hand was used to hold the shield close to the heart.
When mankind invented bows and arrows, that was when weaponry saw its departure from left-right symmetry, with the result that, following standardization, the bow must have been designed to meet the needs of right-handed archers, and the lefties simply had to make-do or attend to other matters, lest they get in the way.
4. Spoken Language
(1) At the same time, primitive man developed a common language, starting with simple expressions for communication, collaboration and teamwork.
They would communicate with one another while engaged in regular activities including hunting, and this meant that, during this sort of work, their Egos were likely to be in the left hemisphere if they were right-handed, and vice versa.
(2) One important and conspicuous development for early mankind that enabled a quantum leap in the sophistication of language use must have been the discovery of fire and its usage in daily life.
Mankind must have first encountered fire in natural forest fires or from volcanic hot ash. Then they gradually learned to tame and keep such fires for long hours to warm themselves, for cooking meals and to keep wild beasts at bay. The next step would have been to learn ways of making new fire without relying on natural sources.
Because of the potential hazards including the burning heat, the need to tend to a fire with care, lest it go out inadvertently or otherwise cause a conflagration (water was indispensable), there had to be expertise for handling as well as skills for creating fire. This gave rise to an urgent need for mutual cooperation and education that covered crisis management, and this compelled mankind to introduce new words, sounds and hand gestures into the existing language, for quicker and more effective communication.
(3) Thus they developed areas within the brain specialized in the use of the spoken language, preferably within the hemisphere contralateral to the hand they habitually used, and because they found it easier to use the right hand when handling fire, these language areas developed chiefly within the left hemisphere.
This way, the Ego could be positioned and remain in the left hemisphere to oversee right hand movement for tending to the fire and, at the same time, speak out to communicate with others using the current language, without extending itself into the right hemisphere or switching brain hemispheres.
In other words, the use of fire prompted mankind to consistently use the right hand, thus promoting right-handedness, and at the same time develop a language area within the left hemisphere of the brain.
The next important development must have been the creation of writing systems for keeping records. Those who lived during such an early age must have noticed that, for exactly the same sequence of letters, the writing looked somewhat different depending on whether the right or left hand had been used for jotting it down, including the slant.
So there must have been a gradual forming of consensus on which hand should be used for writing that looked clear and smart for most people, and this resulted in a standard format for writing, which was generally biased to favor those who were right-handed in most languages.
Some may have pointed out in those days that, since the scribes had to create written records on stone and other hard material using chisels before the advent of clay tablets and paper, it would be best for them to decide on the general rules of penmanship, including the particular hand to be used for carving out formal records, and the scribes may have opted for the right hand.
For these reasons, when man created tools, weapons, musical instruments or writing systems, they were inclined to be for the right-handed, so that the righties were at an advantage from the outset, e.g. the right-handed handshake; the lefties simply had to be resigned and try to be flexible.
Under these circumstances, parents would try to encourage right-handedness (and discourage left-handedness) to their children from the very outset, i.e. early infancy when they would learn to speak.
This way, right-handedness increasingly gained citizenship, became a majority trait all over the world, and continues to this day.
Why the Language Areas are Left-Sided