In terms of the physiological or biological study of facial expressions, many scientists and researchers agree that "facial expressions involve contractions of individual muscles and muscle groups, caused by messages from the motor cortex and regions subcortical”. However, when it comes to forming a consensus on the functions of facial expressions, there has been controversy over the reasons behind facial expressions, which include evolutionary and cognitive theories, as well as behaviorist ideas. Two focal theories emerged when discussing the functions of facial expressions that have been studied extensively by many researchers; the Emotion-Expression view, which states that the function of facial expressions lies in the expression of the internal emotion that resides within a person (Parkinson, 2005). The behavioral ecology perspective theorizes that facial expressions are voluntary manifestations that serve communicative functions that occur during face-to-face interaction and are not associated with emotions (Parkinson, 2005) . Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay Numerous studies and observations have been developed to test this hypothesis, providing evidence and support for the theories presented. This essay will present and discuss the studies developed in order to draw a conclusion on understanding the functions of facial expressions in humans. Darwin's (1872) idea of ​​facial expressions presented the idea that facial manifestations are evolutionary adaptations, which he expanded by asserting that facial expressions derived from an internal emotional process that would help organisms communicate in this way. than to protect and prepare the body for action. Thibault, 2009). Darwin introduced three principles related to the science or understanding of facial expressions: The first principle “principle of associated useful habits” meaning that facial expressions serve as a direct response to a situation that requires an adaptive emotional response (Parkinson, 2005) , “the principle of antithesis” which is the understanding that expressions are “side effects” of previously relevant associations and counter-associations” (Parkinson, 2005), the third principle is “the principle of action of the system nervous” meaning that facial expressions are the result of a physiological trigger from the nervous system when emotions are felt. states appear (Parkinson, 2005). This hypothesis introduced the Emotion-Expression view, which claims that there is a universal communicative factor in facial expressions. This introduced the research question about the universality of facial expressions and whether they are related to emotion (Thibault, 2009). Darwin's claims and principles about facial expressions were not explored until the 1970s. Researchers then began to gather evidence to test the theory that facial expressions are universal and are directly associated with emotion underlying (Thibault, 2009). Ekman, Sorenson, and Friesan (1969) explored the assertion that “emotions are universal and expressions should be recognized in other cultures.” The researchers showed photos of participants expressing six different emotions and asked participants to assign the term that best matched the feeling depicted in each photo. The results yielded high accuracy rates. However, critics have questioned the validity ofexperience because participants “may have” recognized facial media from Western media (Keith Oatley, 2006). Ekman and Friesan (1971) conducted additional research to provide stronger evidence for understanding the emotional expression of facial expression. The study was conducted among those who had little or no contact with Western culture. Again, participants were presented with photographs showing a variety of facial expressions. , combined with a story linked to the expressions, and were toldchoosing the photograph that best fits the story. The universality hypothesis was supported in the results, as accuracy rates were significantly high. Ekman and Friesan (1971). Sorenson (1976) questioned the study conducted by Ekman and Friesan (1971) by claiming that the researchers influenced the responses due to methodological artifacts. The materials used in the study were also criticized as each story presented to the participants was associated with an emotional term, the themes of the stories were also criticized for being based on a Western approach (Mandal, 2015). Despite the many controversies surrounding the studies by Ekman et al. on the universality of facial expressions and their connection to the underlying emotion, more than 70 studies have supported the universality hypothesis, demonstrating that emotions in facial expressions are universally recognized (Matsumoto, 2008). Many of these studies, however, have merited criticism due to the fact that they were conducted in controlled environments and may not reflect real-world situations (Matsumoto, 2008). To challenge the inaccuracy of laboratory research, one study produced additional compelling evidence for the universality hypothesis by observing the spontaneous expression of emotions in victorious and defeated athletes competing in the Olympic Games; finding that athletes born with visual impairment had the same facial expressions as athletes without this disability, further confirming that expressions do not differ due to culture and are instead innate in organisms (Matsumoto, 2008). Although psychologists have divergent opinions regarding the universality of the expression of emotions, one consensus concerns "the principle of action of the nervous system", according to which there is a universality in certain expressions triggered by certain emotions such as fear and surprise which serve as survival based skills. Susskind et al. (2008) found that participants expressing the emotion of fear showed specific physiological changes, such as enlarged visual fields and faster eye movements, which is linked to Darwin's theory that facial expressions can serve to an organism preparing to act in a threatening environment. Further studies conducted by Anderson (2008) observing the expression of surprise found that the physiological changes expressed with the emotion of surprise were similar to the expression of fear. A study conducted by Daniel et al. (2014) observed a stimulus that occurs with the expression of emotions of anger and disgust, finding that stimulus detection increases when the eyes are enlarged and that narrowing the eyes during the sensation of disgust results in discrimination, these physiological changes increasing the sensitivity or consciousness of organisms. These results demonstrate the theory that facial expressions result from triggers in the nervous system when placed in an environment requiring defense or action. Although facial expression theory is used for the expression of emotions, academics.