Horses are capable of making complex facial expressions just like humans and chimpanzees, a new study has found.
The research, published in the journal PLOS ONE, found that horses can produce 17 discrete facial movements – more than dogs, monkeys and chimpanzees.
The study was carried out by a team of researchers from the Universities of Sussex and Portsmouth, and Duquesne University in the United States.
They found that, like humans, horses use muscles underlying various facial features, including their nostrils, lips and eyes, to alter their facial expressions in a variety of social situations.
They identified these facial expressions using the Equine Facial Action Coding System (EquiFACS), which identified 17 discrete facial movements in horses. This compares with 27 in humans, 13 in chimps and 16 in dogs.
Co-author of the study, Dr Bridget Waller from the University of Portsmouth, said: “Humans and other primates exhibit communication skills more complex than any other mammals, because they have been selected throughout evolution to live in large social groups. As horses are not closely related to primates we didn’t expect to see similar specialisation for facial communication.
“However, like dogs, they have undergone significant changes during domestication, and their ancestors also lived socially. So this study suggests that there may be other evolutionary routes to complex facial expression, such as through artificial selection processes like domestication.”
The researchers analysed video footage of a wide range of naturally occurring horse behaviours to identify all the different movements it is possible for horses to make with their face.
Dr Waller said: “Many of the additional facial movements that horses can make actually involve the ears so it could be their ear movements that make the difference to their facial expressions.”
The scientists also carried out an anatomical investigation of the facial muscles that underpin these movements. Each individual facial muscle that was found can now be identified when examining horse facial expressions.