Traditionally, we’ve looked to a toddler’s movements to see if their right or left handed. How they hit a cricket bat, kick a soccer ball, hold a paintbrush and, eventually, learn to write.
Now, however, researchers in Germany have shown how handedness can be identified in the womb, at as early as 13 weeks, and that the asymmetry originates from the spinal cord (not the brain, as originally thought).
In grown humans, arm and hand movements are initiated via the motor cortex in the brain, which sends signals down the spinal cord to trigger the corresponding movement.
But, in the womb, hand movements - a preference for handedness, even - are apparent long before the motor cortex and spinal cord are connected. This observation led researchers to believe the asymmetry originates in the spinal cord, not the brain after all, Science Daily reports.
German scientists analysed gene expression in the spinal cord between the eighth and twelfth week of pregnancy.
They detected significant differences between right and left markers in the spinal cord segments responsible for controlling movement in the arms and legs. According to Science Daily, these differences were apparent from the eighth week of pregnancy and, from the 13th week of pregnancy, unborn children will have a preference for sucking their right or left thumb.
It's a bonus piece of information new parents can garner while viewing an ultrasound: You'll know which end of the garden to set up the soccer goal, and you can load up on left-handed scissors if need be!
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