This is the real reason that you’re left or right-handed

Posted by
Sonya Barber
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New research reveals why you use the hand that you do – and it’s not what you’d expect.

If you’ve ever wondered why you’re a lefty or a righty, you may have just assumed that you were taught it when you were little, or that it was because of activity on one side of your brain. 

Well, it turns out, it’s neither. Researchers from Ruhr University Bochum in Germany have found that you develop a preference for one hand in the womb as early as the eighth week of pregnancy – and it’s actually down to what’s happening in your spinal cord, not your brain.

From analysing gene expression in the spinal cord during the eighth to the twelfth week period, they discovered that gene activity in the spinal cord is already asymmetrical in the womb. 

Ultrasounds show that preference for moving one particular hand develops from the eighth week of pregnancy, and unborn children prefer to suck either their right or their left thumb from the thirteenth week.

The study authors explain that “precursors of a choice of handedness” can be observed in babies in the womb even before the motor cortex in the brain has connected to the spinal cord.

“These results fundamentally change our understanding of the cause of hemispheric asymmetries,” they concluded in the journal eLife.

So, there you have it. Next time you’re holding a baby, they’ll already know which hand to grab your necklace/hair/nose with. 

Images: Lyndsey Marie/iStock