A recent study of horse facial expressions has revealed evidence of evolutionary parallels in how horses and humans make faces.
Horses are primarily visually-oriented creatures. And like humans, horses use their faces to communicate. They use muscle movements to manipulate their eyes, lips, and nostrils in order to form facial expressions in a social context. However, the significance and social function of horses' facial movements has long been overlooked by science, according to the study's co-lead author, doctoral researcher Jennifer Wathan.
Mammal communication researchers at the University of Sussex, the University of Portsmouth, and Duquesne University developed a coding system, the Equine Facial Action Coding System (EquiFACS), to study horse facial expressions. The coding system identifies and catalogues individual facial expressions by analyzing the muscle movements used to form them.
In order to identify all the possible facial movements possible for horses, the researchers took a two-pronged approach. They poured over video footage of naturally occurring horse behaviors. They also examined the anatomical features of horses' facial muscles with regard to how those muscles were used to generate specific facial movements. Each identifiable facial movement was then given a code.
Using EquiFACS, the researchers identified 17 unique facial movements (called "action units") in horses. Humans have 27 such "action units," chimps have 13, and dogs have 16. Wathan notes that in spite of the differences in horse and human facial structure, researchers found parallels in the way humans and horses move their lips and eyes to form communicative facial expressions.
Professor Karen McComb, a co-lead author of the study, notes that EquiFACS has yielded evidence that supports the notion that social factors have played a key role in the evolution of facial expressions across a variety of species.
"It was previously thought that, in terms of other species, the further away an animal was from humans, the more rudimentary their use of facial expressions would be," McComb said.
But this new research has shed light on a much different reality by revealing an added degree of complexity in the social lives of horses.
According to the researchers, the next step in this endeavor is to examine how these identifiable facial expressions correspond to horses' emotional states. And while EquiFACS will go a long way toward illuminating that particular relationship, it also has the potential to become a useful tool in a broader sense. McComb believes that the data it yields will prove valuable to veterinary science and animal welfare practices.
Want to learn more about this exciting new research? Check out the EquiFACS study here.