We all must have seen in our environment that some people are left handed, and the most of the human population is right handed. As per data roughly 1/10 of the human population is left handed. Interestingly no other mammal apart from humans and bipedal mammal – Kangaroo on this planet show preference of hands. Obviously this tells us that handedness i.e. more usage of one hand over the other started to happen after the species split of humans from its closest cousin chimps.
Is handedness genetic?
If you ask me about the name or names of the genes responsible for being right or left handed. My simple answer would be ‘Folks- no such names exist’. Till today scientists could not identify a single gene responsible for hand preference. However, they do not completely deny the role of genes in this trait. According to scientific data, multiple factors act in parallel for the final picture. To prove the connection between genes and hand dominance, the ratios of child born with right hand or left hand preference were estimated based on the parent’s dominant hand. Surprisingly, consistent ratios were found. I have given a detailed chart below. This immediately tells us a hand preference is not a choice of a person. Instead it a trait we are born with.
When did left and right handedness emerge?
Archaeological evidence shows that the human population has shown this trait even before 500,000 years back therefore it is difficult to mark the year of its emergence. The 130,000 year old fossil records of the marks on the teeth of Neanderthals excavated from Croatia directs towards the right hand dominated population. In the history of mankind none of the human populations had large numbers of left handed people. The obsession of using right hand has deep rooted cultural connections. Interestingly in many parts of the world children are forced to use their right hand also called as the proper hand. This raises the question that despite being in smaller numbers why and how left handed traits survived in the reel of evolution.
Do humans prefer one side of their body over the other?
Yes, humans do prefer one side of their body more than the other. But It doesn’t mean we can ignore critical functioning of the other part. For example in spite of us either being left handed or right handed, we need both our hands to function. For example, cutting a salad, holding a gadget, driving a vehicle, taking a bath, putting a nail in the wall. This means we are depend on either left or right hand only during fine motor skills like writing, playing a sport, in combat, eating. Therefore human brain plays a crucial role in hand usage.
Human brain consists of two different parts also called as left hemisphere and right hemisphere. Interestingly in vertebrates, the left side of the brain controls the right side of the body and vice versa. This is also called brain lateralization which is quite extreme in humans as compared to any other animal. Scientists predict that brain lateralization could be one of factors responsible for showing body asymmetry and hand dominance.
What are the benefits of left hand dominance? Why is evolution interested in keeping a few lefties?
The existence of small proportions of left-handed people in a right-hand dominant world indicates the presence of survival benefits associated with lefties over righties. Otherwise, the trait would have been wiped out long ago. Also, a recent study has shown that the ratios of left versus right handed people direct towards the cooperative and competitive type of human evolution.
Now let me explain you about competitive pressure of evolution? It simply means involvement of combats, fist fights, competitive sports etc. for resources which includes food, shelter and partners during human evolution. Obviously the fittest among the competitors will win the resources and leave his/her progeny on the earth.
Although in a right-hand dominant world both lefties and righties competitors have spent most of their time and energy in getting trained with righties. Certainly in such a world being left-handed has a clear advantage as an attack from a left-handed person can surprise his/her right/left-handed opponent. The right-handed opponent will not be able to predict the direction of the blow (attack) and will be at a disadvantage.
For example, left-handed hitters in baseball sport have a slight advantage over the right-hand hitters. Researchers believe that this advantage of the surprise element could be one of the reasons for the presence of small ratios of lefties in a competitive and cooperative type of human evolution.
Myth busters
People often tries to connect the link between logic, creativity, intelligence and luck with handedness or brain hemispheres. Undeniably it is one of the most widespread myths being circulated. We cannot simplify the complexities of brain lateralization without understanding its true nature. Therefore the media circulated myth of people either being ‘left brained dominant’ or ‘right brained dominant’ needs to be stop as it is an oversimplification of brain function mechanism.
Reading sources
- “All kangaroos are lefties, scientists say”. Sci-News.com
- McManus, I. (2009). The history and geography of human handedness. In I. Sommer & R. Kahn (Eds.), Language Lateralization and Psychosis (pp. 37-58). Cambridge: Cambridge University Press.
- McManus IC, Davison A, Armour JA. Multilocus genetic models of handedness closely resemble single-locus models in explaining family data and are compatible with genome-wide association studies. Ann N Y Acad Sci. 2013.
- Probaseballinsider.com/advantages-of-being-a-left-handed-hitter/