The James-Lange theory of arousal is the idea that emotions are the result of changes. William James and Carl Lange, two scientists who studied physiology, came up with this theory in the late 1800s. The theory goes like this: let's say you're about to give a speech. According to the James-Lange theory, you're nervous, your heart races, and your palms sweat. These changes cause your Emotions—in this case, anxiety. Though the idea seems simple enough, there was (and still is) a lot of debate.