• Question: why are some people left or right handed and why not both

    Asked by sdkfz 222 to Rob on 18 Nov 2014.
    • Photo: Robert Hampson

      Robert Hampson answered on 18 Nov 2014:


      This is a complex question.

      Developmental psychologists hypothesise that the brains two sides divide tasks between them. Most people do verbal processing in the right hemisphere which leaves spatial and physical processing in the left hemisphere (which controls the right side of your body) making you right handed.

      There does not seem to be any single gene that explains the phenomena of handedness but it does seem to be inheritable.

      Males expose to a hormone called diethylstilbestrol before birth are more likely to be left handed. We don’t know why. It also seems ultrasound scans can make a baby more likely to be left handed.

      The position of a baby before birth also strongly correlates with handedness. However, this may be a symptom of the baby already having chosen a dominant had and putting itself in a position it prefers. This pre birth position seems to correlate with the inner ear vestibulae which control balance. The asymmetry of the vestibular cortex (the bit which controls the signals from the vestibular in the brain) correlates even more strongly with handedness.

      So in essence, we don’t really know…

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