According to new findings out of Cornell University, the expressive movements of pectoral appendages (wings in birds, forelegs in mammals—and arms in humans) are controlled by the same brain circuits as vocal communication. And researchers have traced those circuits back to a particular region of the brains of our ocean-dwelling ancestors. So if you knock over a glass in a heated dinner-table debate, just chalk it up to evolution. After all, we are wired to gesticulate.

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