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 subcortical regions." However, when it comes to forming a consensus regarding the functions of facial expressions, there has been controversy about the reasons behind the facial displays, which include evolutionary and cognitive theories, as well as behaviorist ideas. Two focal theories have emerged from the discussion of the functions of facial expressions which have been studied extensively by many researchers; the emotion expression view, which states that the function of facial expressions lies in the expression of internal emotion found within a person (Parkinson, 2005). The behavioral ecology view theorizes that facial expressions are voluntary displays that serve communicative functions that emerge 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 Shouldn't Be Banned"? Get an original essay Many 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 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 displays are evolutionary adaptations, an idea which he expanded by stating that facial expressions resulted from an internal emotional process that would aid organisms in communication as well as protect and prepare the organism into action. Thibault, 2009). Darwin introduced three principles in relation to the science or understanding of facial expressions; The first principle “principle of associated useful habits” which means that facial expressions serve as a direct response to a situation requiring 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 nervous system”, which means that facial expressions are the result of a physiological trigger arising from the nervous system when emotions occur, states arise (Parkinson, 2005). This hypothesis introduced the emotion-expression view, which supports the claim that there is a universal communicative factor in facial expressions. This introduced the research question of universality of facial expressions and whether they are interconnected with emotions (Thibault, 2009). Darwin's claims and principles about facial expressions were not explored until the 1970s, researchers then began gathering evidence to test the theory that facial expressions. they are universal and have a direct association with underlying emotions (Thibault, 2009). Ekman, Sorenson, and Friesan (1969) studied the statement that “emotions are universal and expressions should be recognized by other cultures.” The researchers showed images of participants expressing six different emotions and asked participants to assign the term that best fit the feeling illustrated in each photo; the results showed high accuracy rates. However, critics doubted the validity of the experiment because the participants “possibly” recognized facial media from Western media (Keith Oatley, 2006). Ekman and Friesan(1971) conducted further research to provide stronger evidence of emotional expression understanding of facial expression, the study was conducted among those who had little or no contact with Western culture, again participants were provided photographs that showed a variety of facial expressions, paired with a story related to the expressions, and were told to choose the photograph that best fits the story. The universality assumption was confirmed in the results, as accuracy rates were significantly high. Ekman and Friesan (1971). Sorenson (1976) questioned the study conducted by Ekman and Friesan (1971) stating that the researchers had influenced the responses due to method artifacts. The materials used in the study were also subjected to criticism as each story presented to the participants had an emotional term associated with it, the themes of the stories were also criticized for being based on a Western approach (Mandal, 2015). Despite the numerous controversies surrounding the studies by Ekman et al. on the universality of facial expression and whether they are interconnected with underlying emotions, over 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 research conducted in controlled environments and may not reflect real-life situations (Matsumoto, 2008). To challenge the inaccuracy of laboratory research, one study produced further compelling evidence in favor of the universality hypothesis by observing the spontaneous expression of emotions in both victorious and defeated athletes competing in the Olympics; finding that athletes born with a visual impairment had the same facial expressions as athletes without this disability, further confirming that expressions do not differ due to culture and are rather innate in organisms (Matsumoto, 2008). Although psychologists have differing opinions regarding the universality of the expression of emotions, there is consensus regarding the “principle of action of the nervous system”, that there is universality in some expressions that are triggered by certain emotions such as fear and surprise that serve survival-based skills. Susskind et al. (2008) found that participants expressing the emotion of fear represented specific physiological changes, such as enlarged visual fields and faster eye movements, which relates to Darwin's theory that facial expressions can serve the purpose of an organism that prepares for action 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. Providing further evidence that facial expressions served for survival and evolutionary functions was a study conducted by Daniel et al. (2014) observed the stimulus that arises with the emotional expression of anger and disgust, finding that stimulus detection increases when the eyes are enlarged and the narrowing of the eyes during the sensation of disgust results in discrimination, these physiological changes increase the sensitivity or awareness of organisms. These findings showed evidence for the theory that facial expressions are the result of triggers in the nervous system when placed in an environment requiring defense or action. Although the theory of facial expressions serves the purpose of expressing emotions, academics and researchers have developed other theories related to the purpose.