" A recent invention, vocal language may date back only ca. 200,000 years. As human primates, we have not fully come to grips with the prolonged, face-to-face closeness required for speech. Speaking to a stranger, e.g., stresses our autonomic nervous system's sympathetic (i.e., fight-or-flight) division, which a. speeds our heartbeat, b. dilates our pupils, and c. cools and moistens our hands. The limbic brain's hypothalamus instructs the pituitary gland to release hormones into the circulatory system, arousing our blood, sweat, and fears. "

― David B. Givens , The NONVERBAL DICTIONARY of gestures, signs and body language cues