Study: Horses and humans share facial expressions

SUSSEX, England, Aug. 5 (UPI) -- The history of the horse and mankind are intimately intertwined. More than just history, humans and horses share similar facial expressions. Perhaps the latter explains the former.

As most tellers of failed email jokes can attest, the combination of tone, hand gestures and facial cues are important communication strategies. And this truth isn't lost on horses.

According to a new study, horses utilize the same underlying facial muscles as humans in order to manipulate their nostrils, lips and eyes, allowing them use different expressions for different social scenarios.

Like other social mammals, horses use facial expression to communicate with their peers. The latest research for the first time reveals the full range expressive combinations horses can draw upon when communicating.

"Horses are predominantly visual animals, with eyesight that's better than domestic cats and dogs, yet their use of facial expressions has been largely overlooked," study co-lead author Jennifer Wathan, a researcher at the University of Sussex, said in a press release. "What surprised us was the rich repertoire of complex facial movements in horses, and how many of them are similar to humans."

Using cameras and computer-based analysis, researchers isolated 17 different "action units" -- distinct facial movements -- employed by horses. Humans use 26, while dogs have 16. Chimps use 13.

"Despite the differences in face structure between horses and humans, we were able to identify some similar expressions in relation to movements of the lips and eyes," Wathan said.

Researchers say their analysis, detailed in the journal PLOS ONE, will aid the broader study of how facial expression evolved among social 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," co-lead author Karen McComb said.

McComb and Wathan say they're not looking at how different facial expression correspond with varying emotional states.