Among the many distinctive traits of humans is their ability to communicate with each other. While the most readily apparent form of communication is language, both spoken and signed, human communication also involves body positioning and facial expressions. While other primates,such as chimpanzees and bonobos, also use facial expressions in their communications, humans have faces which are different than those of their primate cousins.
In his book Thumbs,Toes, and Tears and Other Traits that Make Us Human, Chip Walter writes:
“Of the thousands of species of mammals on Earth, the human species owns the most expressive face. It has forty-four muscles, twenty-two on each side, about twice as many as a chimpanzee. These muscles not only adhere to bone, but also to one another and to the skin above them, enabling us to arch our eyebrows expressively or turn on a beaming smile.”
One common misconception in American culture is that it takes twice as many facial muscles to frown as it does to smile. In fact, frowning uses 11 muscles while smiling uses 12.
Charles Darwin, in his 1872 book The Expression of Emotion in Man and Animals, linked facial expressions with distinct emotions. Chip Walter writes:
“Psychologists agree that we use our faces to communicate six primary emotions: happiness, sadness, fear, anger, disgust, and surprise.”
These facial expressions appear to be cross-culturally valid and may have had survival value in human evolution.
Humans are not only social animals, but they are also cooperative animals. In human societies, the ability to recognize individuals is an important trait. In their book From Lucy to Language, Donald Johanson and Blake Edgar write:
“Humans recognize each other by the distinctive constellation of features seen in our skulls, especially in our faces. Although other parts of our anatomy are also unique to each of us, it is our face that immediately identifies us.”
Within the human brain, the fusiform gyrus is actively involved in facial recognition, an important human characteristic. In his book The Believing Brain: From Ghosts and Gods to Politics and Conspiracies—How We Construct Beliefs and Reinforce Them as Truths, Michael Shermer writes:
“Facial-recognition software was built into our brains by evolution because of the importance of the face in establishing and maintaining relationships, reading emotions, and determining trust in social interactions.”
There are, however, some people who lack facial recognition abilities. This condition is known as prosopagnosia and people with this condition cannot recognize people by looking at their faces.
One of the hypotheses regarding the evolutionary origin of language is theory of mind. In their chapter in The Oxford Handbook of Language Evolution, Frederick Coolidge and Thomas Wynn explain:
“Theory of mind refers to the ability to infer the thoughts, emotions, and intentions of others.”
Humans can read facial expressions and there is a tendency to mirror other people’s emotions. This ability to read emotions from facial expressions generally allows social relationships to run more smoothly. Frederick Coolidge and Thomas Wynn put it this way:
“The ability to interpret correctly the actions, intentions, and goals of others may be also considered an important step in successful social interactions.”
There are, however, people who are unable to read or interpret facial expressions. In his book Humans: From the Beginning, Christopher Seddon writes:
“What psychologists refer to rather confusingly as ‘theory of mind’ is the ability to understand what another individual is thinking, and to realise that they can have desires, beliefs and intentions that differ from one’s own. We are not born with this ability: it normally developed during early childhood at between four to four-and-a-half years of age. Autism, while not fully understood, appears to involve impairment to the proper functioning of theory of mind.”
Autism involves an absence of theory of mind and is characterized by impaired social skills and impaired communication. Scott Atran, in his book In Gods We Trust, reports:
“Autism is another form of psychopathology that is increasingly associated with deficits in ‘theory of mind’ and faulty appraisals of social intentions.”
In neuroscience, MRI scans of the brain in a normal person looking at a face show activity in the fusiform gyrus of the temporal lode, but in the brain of a person with autism looking at a face there is no activity in this region.
Autism seems to develop in children within the first 30 months but is often not diagnosed until age four or five. Children with autism have difficulties in acquiring language and half never develop useful language skills. What the data from neuroscience and autism seems to suggest is that the evolution of the human face is closely associated with the evolution of theory of mind and language.
More Human Origins
Human Origins: Making Spoken Language Possible
Human Origins: Eyes
Human Origins: Homo rudolfensis
Human Origins: Transitional Humans
Human Origins: Protolanguage
Human Origins: Homo habilis
Human Origins: The Sounds of Language
Human Origins: Fossil Evidence