Horses and humans share facial expressions, study says

Long faces aside, horses may be more expressive than we thought.

According to a new study, horses use a wide range of facial expressions as social cues – much like humans do. Researchers have identified 17 discrete movements, many of which are also used by humans, despite obvious differences in facial structure. They published their findings Wednesday in the journal PLOS ONE.

It’s no secret that human emotion is inextricably tied to facial expression. But facial expression in the animal world is significantly understudied, says Karen McComb, lead author and professor of animal cognition at the University of Sussex. Until recently, systematic studies on the subject were few and far between – and those tended to focus on non-human primates.

Because equine facial structure is so different than primate facial structure, scientists had overlooked horses as candidates for this sort of communication. But as highly visual and socially complex animals, they are actually well suited for facial expression study, says Dr. McComb.

"They have long-term relationships within their own social group or band," she says. "Neighboring bands also come into contact as they move and feed.... Social living and interacting with multiple individuals, both within and outside the immediate social group, is likely to have selected for enhanced social communication – and we think that facial expression is an important part of this.”

By developing the Equine Facial Action Coding System (EquiFACS), researchers could demonstrate the connection between facial movement and communication. They found that horses were capable of 17 distinct “action units,” or facial movements. Humans are capable of 27. Both horses and humans modify their facial expressions roughly the same way – by using facial muscles to contort the nostrils, lips, and eyes. Horses also express themselves through their ear position, like cats and dogs.

But while McComb and her colleagues were able to map out the expressive capabilities of horses, they have yet to determine how those expressions are used.

"Our work shows that horse facial expressions are quite complex," McComb says. "The next step is to relate particular facial movements and configurations to specific contexts – positive versus negative."

She added, "We’re working on what constitutes the horse 'smile.' "

By linking expressions to different contexts, researchers hope to determine whether those expressions indicate positive or negative emotional states. For those concerned with horse welfare, that would be a major breakthrough.

"Animal welfare is increasingly seen as being as much about the presence of positive emotions as the absence of negative ones," McComb says. "EquiFACS should put us in a position to chart what the positive expressions actually are – as well as making us better at identifying the negative ones."