According to Darwin, Darwin said that emotional behavior originally served both as an aid to survival and as a method of communicating intentions. For example, angry people show their teeth because they have inherited behavior patterns that their prehistoric ancestors needed for fighting. Bared teeth also signal an intention to attack. During the 1880’s, the American psychologist William James and the Danish physiologist Carl G. Lange independently reached another conclusion about emotions.
According to their theory, the James-Lange theory of emotions, people feel emotions only if aware of their own internal physical reactions to events, such as increased heart rate or blood pressure. Some psychologists still believe in the James-Lange theory, but there is little evidence to support it. In 1927, the American physiologist Walter B. Cannon and his associate Philip Bard proposed the Cannon-Bard theory of emotions. Cannon and Bard thought emotions arose only when the hypothalamus, a part of the brain, was stimulated.
They believed the hypothalamus was the “seat” of emotions. Several researchers have since shown that stimulation of different parts of the brain, especially the limbic system, triggers emotions. Several American psychologists have independently developed the theory that there are eight basic emotions. These emotions which can exist at various levels of intensity–are anger, fear, joy, sadness, acceptance, disgust, surprise, and interest or curiosity. They combine to form all other emotions.