Face Muscles
Humans spend more time reading faces than any other part of the body. We can recognize emotions based on a series of facial muscle muscle movements, specifically the facial nerve (Freberg 2016). The facial nerve branches off into five different branches: temporal, zygomatic, buccal, mandibular, and the cervical branch.
Biology
Along with the universal facial expressions recognized across cultures (mentioned on the Universal Faces page) there are other factors that play into Darwin's initial theory that facial expressions were biological. One of those factors is that children are able to learn fairly quickly how to make the universal facial expressions of anger, disgust, contempt, happiness, sadness, fear, and surprise.
The other piece of evidence is that those who are blind from birth are able to have to same facial expressions even though they have never seen these expressions on others. David Matsumoto did work at the 2004 Paralympic Games in which he photographed both seeing and bling athletes making the same facial expressions for both winning and losing (Freberg 2016).
Recognizing Emotions and Facial Expressions
Environment
Even though there are universal facial expressions, there can be variations due to different environments. For example, doctors are trained to show less emotion when talking to patients and patient's families. Another variation would be group settings. When we are alone we are more likely to react with stronger facial emotions than if we were in a group. In the Japanese and Russian cultures when they show emotion through facial expressions it is not as intense as it is other countries, specifically American (Engelmann).
