International Left-Handers Day

People have been wondering for a long time why only 10 percent of the population is left-handed and the remaining 90 percent is right-handed. A study from last year has found the reason why some people favour their left hand from the very childhood.

While there were several misconceptions about how it is connected to one's brain, it is apparently something that is related to the spinal cord.

Previous research discovered that the preference of a baby being left or right-handed has been determined in the mother's womb as early as the eighth week of pregnancy.

Even another study claimed that genetic differences in the left and right hemisphere help decide whether a person was born left handed.

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Meanwhile, a study from 2017, which was originally published in the journal eLife, has shown that the gene activity in the spinal cord is already asymmetrical in the womb — this could cause left or right-handedness.

The study was led by Dr Sebastian Ocklenburg, Judith Schmitz, and Prof Dr HC Onur Gunturkun from Ruhr-Universitat Bochum, along with others from the Netherlands and South Africa.

According to the study, the motor cortex -- which sends a signal to the spinal cord -- can controls the arm and hand movements. On the other hand, the motor cortex and the spinal cord do not connect until about a baby's 15 weeks inside the womb. But the right or left-handedness has been decided long before that.

Hence, it indicates that baby can move arms and choose its favourite hand even before the brain starts controlling the entire body. It concludes that spinal cord is the reason behind left or right-handedness.

To analyse this matter deeper, the researchers also analysed the gene expression in the spinal cord during the eighth to 12th week of pregnancy.

Meanwhile, researchers of the Northwestern University developed a mathematical model in 2012 to show that the percentage of left-handed people is mostly a result of human evolution.

Daniel M Abrams, the author of the model and an assistant professor of engineering sciences and applied mathematics at the McCormick School of Engineering and Applied Science, told LiveScience: "The more social the animal -- where cooperation is highly valued -- the more the general population will trend toward one side.

"The most important factor for an efficient society is a high degree of cooperation. In humans, this has resulted in a right-handed majority."

Although genetic predisposition may be the basis for this, social factor has dictates human evolution after all.