In 2015, scientists discovered that dogs could discriminate between happy and angry facial expressions in humans, and now researchers from the University of Sussex Mammal Vocal Communication and Cognition Research Group have found that horses can as well.
As lead author Amy Smith and her colleagues reported in the latest edition of Biology Letters, they used photographs of human males and found that domestic horses had a negative response to angry expressions, indicating that the domestication process might have caused the creatures to adapt to and gain the ability to interpret human behavior.
According to BBC News and The Guardian, the researchers created high-quality, large-sized color photographs of a man both smiling and baring his teeth, and frowning and baring his teeth to serve as positive and negative emotions. Volunteers then went to riding stables, presented the images to a total of 28 horses and recorded their reactions.
“What’s really interesting about this research is that it shows horses have the ability to read emotions across the species barrier,” Smith told The Guardian. “We have known for a long time that horses are a socially sophisticated species but this is the first time we have seen that they can distinguish between positive and negative human facial expressions.”
Ability may have evolved as a ‘warning system,’ say authors
During the experiments, one volunteer held the horse while another, who did not know which facial expression each of the pictures contained, held up the photographs. In most instances, the horses looked at the angry faces with their left eye, which sends signals to the right side of the brain, where negative stimuli are processed.
Furthermore, heart monitors equipped to the horses found that angry faces caused a significant increase in the heart rate of the creatures. Smith said that the reaction to the negative expressions was “was particularly clear,” telling The Guardian, “There was a quicker increase in their heart rate, and the horses moved their heads to look at the angry faces with their left eye.”
The study authors claim that this behavior has only previously been observed in dogs, and that the impact of facial expressions on an animal’s heart rate had not previously been demonstrated by any heterospecific studies. The findings suggest that domestication of a species could cause it to develop the ability to recognize emotions in humans, according to BBC News.
“It’s interesting to note that the horses had a strong reaction to the negative expressions but less so to the positive,” Smith said to the Atlanta Journal-Constitution. “In this context, recognizing angry faces may act as a warning system, allowing horses to anticipate negative human behavior such as rough handling.”