Do horses grin when they’re pleased, or scowl when they’re angry? Researchers at the University of Sussex have proven that horses use an entire system of facial movements that are analogous to human expressions.
The study calls this system the Equine FACS (Facial Action Coding System), consisting of 17 action units, or discrete muscle movements. Each unique facial movement is used in a different social situation, and many of them appear similar to human action units, despite our vastly different facial musculature.
The finding reflects the complicated social organizations within groups of horses. Like humans and other primates, horses maintain complex relationships via communication. Since they are extremely visual animals, they rely on small but significant changes in facial expression to match a certain social or emotional context.
For example, horses widen their eyes to show more white when they are afraid, just as we do. Another comparable facial action is the Inner Brow Raiser, where horses raise the skin above the inner corners of their eyes in negative situations—notice what happens to your eyebrows when you pout.
Check out some of these facial actions in more detail:
Given the long history of domestication between humans and horses, the dearth of research on their communication methods is a bit surprising. In addition to horses, the original FAC system for humans has been adapted for dogs, cats, and chimps. Humans have 27 discrete facial movements, while dogs have 16, cats have 21, and chimps have 13 . These coding systems are invaluable for training and veterinary use, and they also can improve relations between people and the animals in their lives.
Researchers have yet to test whether horses can understand human expressions, but our canine pals seem to be attuned to our facial emotions.
A study earlier this year trained dogs to touch photos of either a happy human face or an angry one to receive a treat. When presented with new photos, the dogs successfully recognized the same types of expressions, even when they could only see part of the face. It’s possible that the ability to understand our expressions was a favored trait over thousands of years of breeding and domestication.
The overlap between the systems used by different animals, and the synergy between dogs and humans in particular, suggests that, long ago in our evolutionary history, facial expressions were adaptive in some way. These studies add to the evidence that social factors and the need for communication played a key role in the evolution of facial expressions, for all of the species that use them.