Why do we have a dominant hand?

dominant hand

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As that as things age, they tend to get better – a realistic way to define evolution. The basis of this is to refine the loopholes and make a more able person, with higher chances of survival. Compared to the ‘versions’ of humans that came before us, we have (on average) a higher cranial (i.e., brain) capacity, an erect stature and all the things that make us inherently Homo sapiens sapiens, thereby enriching our chances to beat the other Homo sapiens from being the dominant species.

Almost everything in and on our bodies can be used, each of them crucial for us to continue our daily lives. Then why is it that we have a DOMINANT HAND?

man writing

The feature of having a dominant hand is called HANDEDNESS. It is defined as the more precise performance of one of the hands over that of the other – thus referred to as the dominant hand, while the other hand is called the NON-DOMINANT hand. The non-dominant hand is the one that is less preferred to perform tasks by. In humans, 90% of the people prefer the right hand over the left one, making the right hand dominant. While these people use left hand do use in their daily lives, tasks requiring perfection and precision are performed using the dominant hand.

It seems redundant for evolution to continue this trajectory of having a non-dominant hand. An organ with little to no function is usually eliminated in the process of evolution, but since there exists 10% of the population who prefer their left hand, both our limbs are intact. On the other hand, there is a small percentage of the world who can use both hands-

  1. AMBIDEXTRITY is the ability to use both hands with the same level of efficiency. This is a rare quality and most ambidextrous people are born with this ability. Yet, there are people who ‘teach’ themselves to use both their hands equally, but there may be a slight preference present for their originally dominant hand.

2. CROSS-DOMINANCE manifests as a person changing the preferred hand for the task, they are currently engaged in. It is common for only one hand to be comfortable with the given task. This is seen in approximately 1% of the population.

both hand writer

So, what causes a person to have a dominant hand?

Scientists have hypothesized that the preference of one hand over the other is a characteristic decided IN UTERO (i.e., while the fetus is in the womb). This trait is set in stone once the environmental influences come into play. Like various other traits possessed by a person, handedness is also influenced by factors that may be environmental as well as genetic (i.e., that might run in the family).

  1. Effect of the brain

The brain has two hemispheres (parts) – the RIGHT AND LEFT HEMISPHERES. It is known that each hemisphere is responsible for controlling a certain function related to the body – such as motor, thinking, creativity, etc. This division of functions differs from person to person.

A popular theory about handedness refers to this division of ‘labor’, as it is called, between the two hemispheres. This theory suggests that since most people’s left hemisphere controls speaking, the people are right-handed. Similarly, the opposite is true for left-handed individuals, that their right hemisphere is in charge of the function of speaking.

left and right brain

2. Position of the fetus in utero

Another theory that has surfaced the scientific community defines the dependency of handedness on the position of the fetus in utero. As it was stated before, the preference of the dominant hand may be determined in the womb, thus making this theory an extension of the one proposed before.

The position of the fetus in the womb changes through the three trimesters – most babies born in the third trimester are born head-first, but that may not be the case for ones born prematurely. As the positions vary, the fetus exhibits handedness by sucking the thumb of the dominant hand. It is logical to assume that the fetus chooses this hand (based purely on this theory) because of the spatial comfort of the womb. When the position changes, there is a chance for the dominant hand to change as well.

This was deduced because there was a decrease in right-handedness in premature babies, i.e, less than 90% of the premature babies were found to be right-handed, which is a deviation from the natural statistic. So, it was hypothesised that the position of the fetus can determine the handedness.

child in uterus
  1. Genetics

Via a large thread of studies, it has been observed that parents who are both left-handed have a higher chance (i.e., 26%) of birthing a left-handed child as compared to right-handed parents (i.e, 10%). So, the relation of handedness with that of genetics has been tested and can prove to be partially true.

  1. Surroundings

If one disproves the effect of predisposing factors such as genetics on handedness, the surroundings of a child can influence the decision of handedness. While this may not be accurate from a scientific point of view, people claim the reason for their right-handedness being their habits in childhood as enforced by their parents.

Having said this, handedness is a trait influenced by both environmental and genetic factors. Despite the claims of talents being asserted concerning the dominant hand, these do not possess a scientific base. The fact that ambidexterity can be learned proves that no amount of predisposition can restrict a person’s ability to perform a certain task with a specified limb. Yet, handedness is very present in humans, as it has been observed in the other primates as well – such as apes preferring to climb with a dominant arm and in captivity, play with one of the limbs.

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