Is handedness inherited?

Published - January 14, 2023 08:15 pm IST

A person is more likely to be a left-hander if one’s mother is also left-handed.

A person is more likely to be a left-hander if one’s mother is also left-handed. | Photo Credit: AFP

We humans walk with two legs (called ‘bipedal’) and use two hands. The evolution of bipedalism began in our ancestors, the primates, about 4 million years ago. The primates not only gave us our blood groups, but our two feet and two hands as well. Primates exhibit characteristics that distinguish them from less evolved mammals. These include adaptations to live in trees (as monkeys do), big brains, heightened sense of vision, opposable thumbs to grasp the four fingers in each hand, and more flexibility in shoulder movements. 

Four hands to two

Dr. Tetsuro Matsuzawa of the Kyoto University, Japan, writes that the shared ancestor of primates moved into tree tops and developed four hands from the four legs possessed by the terrestrial ancestor. This was an adaptation to arboreal life; enabling the efficient grasping of branches and tree-trunks. Subsequently, early human ancestors left the trees to start walking long distances across the land, bipedally. Thus, we created two feet from four hands during the course of evolution from our primate ancestors. 

The anthropologist Carol Ward of the University of Missouri, U.S. points out that the way we humans get around the world is different from any other animal on earth. We move around on the ground, upright on two feet, but in a unique way: with one foot after the other, holding our body fully upright in a characteristic series of motions. So, it’s a big deal to figure out how and why we walk the way we do, and how our lineage really diverged so much from ape-like creatures. 

The human brain is about three times as big as the brain of our closest living relative, the chimpanzee. Moreover, a part of our brain, called the cerebral cortex — which plays a key role in memory, attention, awareness and thought — contains twice as many cells as the same region in chimpanzees. We are, thus, smarter than apes.

In your genes?

Now comes the question of handedness. About 10% of us are lefties. How did this come about? This is still a hotly debated issue. There may be genetic influences: you are more likely to be a left-hander if your mother is left-handed than if your father is. Your chances rise to 50% when both your parents are left-handed. A group from the Sargodha University in Pakistan, writing in The Journal of the Indian Academy of Applied Psychology (JIAAP), reported that left-handed participants were more intelligent than right-handed participants.

Dr. Chris McManus of the University of London, U.K. has, in 2019, published an authoritative article, ‘Half a century of handedness research: myths, truths, fictions, facts; backwards, but mostly forwards’, in the journal, Brain and Neuroscience Advances. He hopes that with new advances in gene sequencing and brain scanning techniques we will know more about human handedness in the coming years.

Advantage lefties

In sports, as we can imagine, lefties rule over righties. In international cricket, roughly 20% of the top-order batsmen are left-handers. So are 23% of Open-era Wimbledon champions. Gautam Gambhir and Sourav Ganguly in cricket, Rafael Nadal and Martina Navratilova in lawn tennis, and Lionel Messi in football. Mahatma Gandhi was ambidextrous, and so was Isaac Newton. You may add more names to these lists.

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