Why are most people right-handed?
Revealing an enigma of human evolution
🏷️ Categories: Biology
Which hand do you write and eat with?
I'm left-handed.
I am left-handed and when I write I get ink on my hand when I run it over what I have already written.
I am left-handed and I had to write in strange postures when there were no left-handed desks.
Why are there so few left-handers? He always asked me the question.
Brain functions
Being left or right-handed is a brain issue.
About 85% of the world is right-handed and it is more common in women. Due to the configuration of the nervous system, the hemispheres control the opposite sides, that is: the right hemisphere controls the left side of the body and the left hemisphere controls the right side.
It seems that the division into hemispheres is very old and speeds up simultaneous processes (Uomini, 2009). For example, the left hemisphere may be dedicated to searching for food while the right hemisphere is free to react to danger. This happens in fish and birds, which attack prey more frequently when they see it with their right eye (Corballis, 2003).
Incredible true? We are not as symmetrical as we seem on the outside.
Historical evidence
We know when we began to prefer the right hand because of archaeological remains.
Archaeologists have made replicas of ancient stone tools using both left and right hands and then compared these artifacts with tools made by hominins millions of years ago.
Evidence indicates that 1.5 million years ago, Homo habilis and Homo erectus tended to use the right hand (Frayer et al., 2016) and by the time Homo heidelbergensis appeared, about 600,000 years ago, the preference for the right hand was clear. This is known from the wear on the preserved teeth, as they used to grasp things with the right side of the mouth, indicating that they brought those objects to the mouth with the right hand more often (Uomini, 2009).
Sounds interesting, but why does it happen, why do we prefer the right side?
Studies in chimpanzees and the Homo Loquens hypothesis
An interesting theory is that of Homo loquens.
Scientist Stephanie Braccini and her colleagues examined laterality in chimpanzees and found that when they remained on all fours they showed no preference for one hand. However, when forced to stand upright, a preference emerged, although it was 50-50, with some becoming left-handed and others right-handed.
Something else had to happen in human development.
Do you know what?
The language.
Language processing is mostly done in the left hemisphere (which controls the right lateral), it is possible that the preference for the right hand for writing is a consequence of this specialization. As our language became more sophisticated, the tendency to use the right hand grew (Corballis, 2003; McManus, 2002).
It is already making sense.
Left-handers in society
About 10% of the population is left-handed and it is more common in men.
Historically, being left-handed has been stigmatized, and in many cultures attempts were made to force left-handers to use their right hand. In Spain, my country, they were forced to write with the right hand.
In search of the left-handedness gene
Left-handedness appears to have a genetic component.
Studies have shown that left-handedness runs in families. Not much is known, but genetic models by McManus and Annett have found that if a mother is left-handed, her children are more likely to be left-handed.
Finding the gene that determines whether a person is right- or left-handed could help us better understand how the brain works with respect to language. Scientists proposed two ways to search for this gene (McManus, 2002):
Search the X chromosome for a gene responsible for left-handedness.
Search for similar genes in mice: Mice have a gene that determines handedness orientation. Scientists believe that the gene for handedness in humans may have evolved from this gene. So, they search the human genome for genes that resemble this gene in mice.
After some time of research, genes associated with left-handedness were found.
These genes were seen to especially affect language areas (Ocklenburg et al., 2017). It seems that left-handers have more symmetrical connections between the brain hemispheres, which could explain exceptional abilities in areas such as music and mathematics, although it remains somewhat unknown.
In addition, left-handers have an advantage in sports involving quick decision-making and hand-eye coordination, because right-handed opponents do not usually face left-handers (Grouios, 2004).
That has happened to me playing basketball, they once made the comment, "You're left-handed!" because it was harder for them to defend me.
✍️ It's your turn: Have you ever wondered why most people are right-handed? Did you know that left-handed people have the problem of getting their hands dirty when writing? All my life as a student I came back with my hand stained with ink or pencil.
💭 Quote of the day: "The brain is deeper than the sea." Emily Dickinson in The Complete Poems of Emily Dickinson
References 📚
Annett, M. (2002). Handedness and Brain Asymmetry: The Right Shift Theory. Psychology Press.
Braccini, S., et al. (2009). "Hand preferences in captive chimpanzees (Pan troglodytes)." Journal of Human Evolution, 57(2), 101-110.
McManus, I. C. (2002). Right Hand, Left Hand: The Origins of Asymmetry in Brains, Bodies, Atoms and Cultures. Harvard University Press.
Corballis, M. C. (2003). "From mouth to hand: Gesture, speech, and the evolution of right-handedness." Behavioral and Brain Sciences, 26(2), 199-208.
Frayer, D. W., Lozano, M., Bermúdez de Castro, J. M., Carbonell, E., Arsuaga, J. L., Radovčić, J., & Fiore, I. (2016). Right-handed Neandertals: Vindija and beyond. Quaternary International, 409, 58-67.
Grouios, G. (2004). Motoric dominance and sporting excellence: Training versus heredity. Perceptual and Motor Skills, 98(1), 53-66.
Ocklenburg, S., Beste, C., Arning, L., Peterburs, J., & Güntürkün, O. (2017). The ontogenesis of language lateralization and its relation to handedness. Neuroscience & Biobehavioral Reviews, 84, 21-34.
Uomini, N. (2009). "The prehistory of handedness: archaeological data and comparative ethology." Journal of Human Evolution, 57(2), 95-100.
I’m a left-handed woman who grew up just after the period of trying to change us. I feel very left-oriented throughout my body. Now after reading your article, I also feel very special as I give you my left-armed power to the people salute. Thank you. P.S. I’m not good with either math or music (except dancing) but pride myself on my skill with language.
Left handed here too! :)