Charles Darwin proposed that facial expressions are an evolutionary adaptation for communication. He argued that these expressions are not influenced by culture but are universal across species. For example, a snarling expression with exposed teeth signals a threat in many animals, including humans. Darwin also suggested that displaying an emotion can intensify the feeling. Smiling, for example, could enhance one's sense of happiness. This idea laid the foundation for understanding the role of facial expressions in emotional experiences.

The Facial Feedback Hypothesis

Building on Darwin's theory, modern psychologists developed the facial feedback hypothesis, which suggests that facial expressions both reflect emotions and influence them. According to this hypothesis, forming a facial expression sends signals to the brain that reinforce the emotion being expressed. This feedback loop can intensify an existing emotion and, in some cases, even initiate it. For example, forcing a smile can make one feel happier, whereas frowning can evoke feelings of sadness.

Physiological Responses to Facial Expressions

Research supports the facial feedback hypothesis by showing that facial expressions can trigger physiological changes in the body. In one study, actors mimicking fearful expressions experienced an increase in heart rate while their body temperature remained unchanged. Conversely, adopting an angry expression led to an increase in both heart rate and body temperature. These findings indicate that the muscles used in facial expressions may play a role in activating the body's physiological responses to different emotions. As a result, facial expressions serve not only as social signals but also as mechanisms that can modulate emotional states.