Do your facial movements show your emotions? Think again if you think the answer is yes. The question is being debated. According to some experts, people around the world make specific faces that express certain emotions, such as smiling in happiness, scowling in anger and gasping with widened eyes in fear. They point to hundreds of studies that show that smiles, frowns, and so on are universal facial expressions of emotion. The expression of the Emotions in Man and Animals was written by Charles Darwin.

Other scientists point to a mountain of counterevidence showing that facial movements are not the same as emotional meaning. When they hear a bad pun, people may smile in hatred and scowl in delight. A wide-eyed gasping face is a symbol of aggression in Melanesian culture. The experts say the expressions are just cultural stereotypes. Both sides in the debate acknowledge that facial movements vary for a given emotion, but they disagree about whether there is enough uniformity to detect what someone is feeling.

The outcome of the debate has serious consequences. Artificial intelligence can be used to evaluate your facial movements during an interview, which can lead to you being turned down for a job. Sometimes a judge or jury will impose a harsher sentence if they think a person has a lack of remorse. Children in preschools across the country are taught to see smiles as happiness, scowls as anger and other stereotypes from books, games and posters. The teachings do not translate to better communication for children on the autism spectrum.


Who is right? The answer involves a doctor, a scientific error and a century-long misinterpretation of Darwin's writing. His own observations offer a solution to the modern understanding of emotion.

The assumption of universal facial expressions can be traced back to a set of photographs by French physician Guillaume-Benjamin-Amand Duchenne. In the early days of photography, Duchenne stimulated people's facial muscles and photographed them.

Darwin proposed in Expression that certain facial movements were universal signs of emotion. Darwin wrote that people smile in happiness. They frown in sadness. The way the story is usually told, Darwin discovered that emotions have innate, biologically based expressions that are universally recognized and shared with other animals. The story shows how facial movements can be used to detect a person's emotional state and give you important information to keep you and them healthy.

It would seem that way. Darwin's mistake was a doozy, as there was a lot of evidence that he was wrong. People express a given emotion with great variability. In anger, people in urban cultures only scowl 35 percent of the time, according to meta-analyses of studies measuring facial movement during emotion. Scowls are not specific to anger because people scowl for other reasons, such as when they are concentrating or when they have gas. Every emotion studied and every measure that tells us about someone's emotional state is the same.

Artificial intelligence systems do not detect emotions. Physical signals, such as facial muscle movements, are not psychological signals. In Western culture and science, the conflation of movement and meaning is very important. A recent high-profile study applied machine learning to six million internet videos of faces. The human raters who trained the artificial intelligence system were asked to label facial movements in the videos, but only emotion words were given to use.


Evidence shows that facial movements are just one signal of many in a larger array of contextual information that our brain takes in. People may see pain or frustration if they are shown a grimacing face in isolation. If you show the same face on a runner crossing the finish line of a race, you will get the same grimace. The face is a weaker signal of a person's internal state than other signals.

Darwin suggests that instances of a particular emotion, such as anger, share a distinct, immutable, physical cause or state, that makes them similar even if they have superficial differences. Scientists have proposed a variety of essences, some of which are easily seen, such as facial movements, and others, such as complex, intertwined patterns of heart rate, breathing and body temperature, that are only observed with specialized instruments. The belief in essences is compellingly intuitive. It is difficult to prove that an essence doesn't exist. People who believe in essences but don't observe them often continue to believe in them. Researchers tend to justify their belief by suggesting that tools and methods are not enough to locate the essences they seek.

The solution to this dilemma can be found in Darwin's book On the Origin of Species, which was written 13 years before Expression. It is celebrated for helping biology escape the paralyzing grip of essentialism. Before Origin was published, scholars believed that each biological species had an ideal form, created by God, with defining properties that distinguished it from all other species. The dog show is a version of biology. Each competitor is judged against a hypothetical ideal dog. Deviation from the ideal is an error. Darwin's Origin proposed that a species is a vast population of varied individuals with no essence at its core. The ideal dog doesn't exist, it is a statistical summary of many different dogs. Natural selection by the environment depends on variation. Darwin ignored his most important discovery when it came to emotions.

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The power of essentialism led Darwin to absurd ideas about emotion, such as that an emotional imbalance can cause hair to fall off and that insects can cause fear and anger by rubbing their body parts together.

The idea that emotions evolved via natural selection to serve important functions seems to lure designers of emotion systems to follow this comfortable path. You will find that Darwin barely mentioned natural selection if you read Expression. He did not write that facial expressions are functional. He wrote that smiles, frowns, eye widening, and other physical expressions were meaningless and no longer serve a function. He made this statement more than 10 times. Darwin believed that humans are animals and have evolved. If we share expressions with other animals, but they are useless for us, they must have come from a long-gone common ancestor.


For more than 100 years, expression has been cited wrongly. How did this happen? Floyd Allport was a psychologist in the early 20th century. In his 1924 book Social Psychology, Allport made a sweeping inference from Darwin's writing to say that expressions begin as vestigial in newborns but quickly assume useful social functions. The descendant serves as a basis for the latter and the biologically useful reaction is not present in the descendant.

Allport's idea was attributed to Darwin and eagerly adopted by like-minded scientists. They can now claim to be the heirs of Charles Darwin and write about facial expressions as universal. With a single sentence, Allport misdirected the Western understanding of emotions, not only in science but in law, medicine, the eyes of the public and now emotion artificial intelligence systems.

This scientific tale has a happy ending because there is a name for the kind of variation we observe in real-life instances of emotion. It is the same variation that Darwin observed in animal species. Darwin described an animal species as a collection of varied individuals with no biological essence at its core. Population thinking is supported by the modern study of genetics.

Darwin's expression is a historical text, not a scientific guide. Science is not truth by authority. Science is the study of doubt in different contexts. Scientists can be wrong. There are mistakes in the scientific process. There are opportunities for discovery.

The views expressed by the author or authors are not necessarily those of Scientific American.