On the left hand, there are no easy answers

Humans are asymmetric animals. Early in our embryonic development, the heart turns to the left. The liver develops on the right. The left and right lungs have distinct structure.

There are certain rare syndromes in which the usual asymmetry of organs is reversed — I remember how disconcerting it was the first time I examined a child with dextrocardia, a heart on the right side, and heard the heart sounds in unexpected places. But when it comes to handedness, another basic human asymmetry, which reflects the structure and function of the brain, the reversed pattern is relatively common, and for all that, not easily understood.

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