A new study has found that horses can recognize and respond differently to smiling versus angry human faces.
In a paper published Wednesday in the journal Biology Letters, researchers from the University of Sussex in the United Kingdom have shown that when horses are shown photographs of angry men, their heart rates increase, and they tend to viewing the photo with their left eye instead of the right.
Previous work has shown that horse’s heart rates correlate with their level of stress. And the second finding isn’t as strange as it sounds—a number of mammals, including humans, tend to disproportionately rely on their left eye when looking at “negative stimuli,” write study lead author Karen McComb and first author Amy Smith in an email.
“The preferential use of the left eye when viewing a threatening situation is an evolutionary adaptation,” they note. “Information from the left eye is processed in the right brain hemisphere, parts of which are specialized for handling threatening information.”
This is the first proof that horses can distinguish certain human emotions, only the second animal proven capable of such a feat. Dogs, too, appear to be able to recognize angry human faces, as shown in a 2012 study in PLOS ONE.
What makes the finding all the more noteworthy is that horse faces structurally very different from humans, meaning that the animals must be basing their judgments on more than their ability to perceive other horses, and that the response was based solely on a photograph, which lacks all of the details of a live person, such as body language and affect. They speculate that other animals may have similar abilities.