So much for one trick ponies. New research from the UK shows that horses not only have the second-most facial expressions of any animal, but that many of their expressions closely resemble humans.
The study, published Tuesday in the journal Plos One, examined the facial expressions of 86 horses using 15 hours of video footage and a tool called The Equine Facial Action Coding System (EquiFACS). Observing things like eye movement, lip placement, and teeth exposure, lead authors Dr. Jen Wathan and Dr. Anne Burrows shed light on possible evolutionary links between the two species.
While previous research on horse’s expressions of pain has been performed, the study is the first to investigate and record the full range of expression, and to analyze its similarity to humans. Previous hypotheses held that horses, when far away from humans, would have facial expressions that were more “rudimentary.”
On the contrary.
Footage of horses separated from humans yielded a total of 17 different facial expressions—one more than dogs and four more than chimpanzees. Humans have a total of 27 facial expressions and the difference between the face shapes is significant. Horses have laterally placed eyes and an elongated face; humans have frontal eye fields, smaller faces, and at least 43 facial muscles.
Given these discrepancies, the researchers weren’t holding on to hope of finding a connection. “We didn’t expect horses to have any similarities with humans at all,” co-author Dr. Jen Wathan said in an email. “They’re two such distantly related species and, at first glance, have such differently shaped faces.”
The EquiFACS coding system, a joint effort between researchers at The University of Sussex, the University of Portsmouth and Duquesne University, cataloged the placement of each muscle and structure. Lip pucker, chin raiser, mouth stretch, and ears forward are among the terms used in the paper to catalog the varied faces.
Most intriguing about the facial expressions, and their similarities to humans, is the implications that finding has on evolution. The authors theorize that the conclusion means one of two things: that the facial expressions of our ancestors were preserved in certain species, or that humans and horses followed similar evolutionary paths.
It’s a topic Margo DeMello explores in her book, Faces Around the World: A Cultural Encyclopedia of the Human Face. “Human facial expressions, and the emotions they express, have their roots in animal expression,” she writes. DeMello says the theory came out as early as 1872, when Charles Darwin pointed out that, like humans, animals convey emotion through their face.
So what are these shared expressions between horses and us? Wathan, a co-lead author of the study, elaborated for The Daily Beast: “One example is that horses and humans can both raise the skin above their eyes, which seems to happen in negative emotional situations,” she writes. “Another example is the retraction of the lip corners, which seems to be part of a submissive gesture in horses.”
With better eyesight than both cats and dogs and a “complex” set of muscles in their lower faces, horses are able to display a large range of feelings—which they likely use to communicate. “Horses have quite rich social lives, where they have many close range interactions with other members of their species,” writes Wathan. “Visual communication and a good ability to be able to perceive visual signals seem as though they would be adaptive in this situation.”
Dog and cat lovers may be surprised to hear that, despite strong bonds, horses’ facial expressions more closely align with our own. Cats still come out on top, in a way. With 21 facial expressions, they boast the most of any animal. Cue the horse grimace.