Cannon was interested in the strange physiological changes produced by powerful emotions. In all mammals, rage, anger, and fear produce an assortment of peculiarity: heart rates speed up, pupils dilate, nostrils flare, muscles tighten, digestion ceases, senses perk and sharpen—the list goes on. Around 1916, Cannon decided these disparate reactions were actually a global response by the nervous system to extreme stress, a response with a purpose: increase strength and stamina. Cannon had discovered the “fight-or-flight response” and this rewrote the rule book.
