Left-handedness may have nothing to do with the brain

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If you’re a leftie, you probably think your brain dictated which arm would be your dominant one. A study published last year, however, has shown that it might have nothing to do with your brain.
Rather, it could be determined by your spinal cord while you are in the womb.

Left handedSince the 1980s, research has shown that our preference for being left or right-handed is probably determined in the womb before we are born – as early as the eighth week of pregnancy. Ultrasound scans have shown babies sucking their dominant thumb from week 13 in the womb, leading scientists to think that the genetic differences in the left and right hemisphere of the brain would determine whether someone was born left or right handed.

The latest study, led by Dr Sebastian Ocklenburg, Judith Schmitz, and Prof Dr HC Onur Gunturkun from Ruhr-Universitat Bochum, along with others researchers from the Netherlands and South Africa, has shown that gene activity in the spinal cord is already asymmetrical in the womb, and that this could cause left or right-handedness.

According to the study, the motor cortex (which sends a signal to the spinal cord) can control arm and hand movements. However, the motor cortex and the spinal cord do not connect until baby's 15th week inside the womb. With right or left-handedness being decided long before that, the researchers concluded that since a baby can move its arms and choose its favourite hand even before the brain starts controlling the entire body, the spinal cord is the reason behind left or right-handedness.

The researchers also analysed gene expression in the spinal cord during the eighth to 12th weeks of pregnancy. They concluded that the asymmetrical nature of the spinal cord could be the result of epigenetics, which dictates how organisms are affected by changes in their genes' expressions, rather than in the genes themselves. These changes are often brought about by environmental influences, and can affect how the baby grows, and could affect the right and left spinal cord differently, resulting in lefties and righties.

These findings, however, are still not definitive. In fact, research conducted in 2012 provides another – equally valid – answer as to why 90% of the population is right-handed: human evolution. Researchers at Northwestern University developed a mathematical model hypothesising that a balance of co-operation and competition in our evolution has led to the left-handed-right-handed divide.

“The more social the animal — where co-operation is highly valued — the more the general population will trend toward one side,” 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 most important factor for an efficient society is a high degree of cooperation. In humans, this has resulted in a right-handed majority.”

This finding will probably come as no surprise to left-handed people. The research points to the fact that we have evolved to favour right-handedness, and anyone deviating from this may have been conditioned to grow up this way, despite their genetic predisposition – a situation that was common until relatively recently. These days, though, there are specific products catering to lefties, from scissors to golf clubs, to corkscrews, and even specially angled pens, making life easier and helping them to use their “right” hand.

Image credit: Copyright: alfonsodetomas / 123RF Stock Photo


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