“More than just a smile” – Horses distinguish between human happy vs. angry faces and act accordingly

I dedicate this Blog to my ever smiling friend Stefanie Flynn and her three Iceandic rascals.

Did you know that Charles Darwin, known for his contribution to the understanding of evolutionary biology, was the first scientist to systematically describe the role of emotions? In his book “The expression of the emotions in man and animals” (1872) he analyzes in detail human and non-human expressions of emotions. 

Socially living animals usually have an elaborated intraspecies communication system. They convey among each other many different emotions such as bonding, but also aggression and submission. Especially the communication of aggression and submission contributes to the avoidance of intraspecies conflict and thus injuries, which leads to an evolutionary advantage for the species. 

Many animals express their emotional state at least as much through body posture as through facial expressions. During the evolution of the primate, facial expressions of emotions became more relevant, e.g. Schimpanzees and Bonobos have “naked” faces, which facilitates the recognition of facial features. Thus, it is probably not surprising, that humans communicate more than any other primate or mammals in general through facial expressions. 

In order to understand the fundamental effect facial expressions of emotions have, I would like to invite you to a little self-experiment. Please klick on the button below and watch the figure for about 15 sec. How and what do you feel?

Now you can klick the image away by klicking on it once again.

Now the next trial: Again, click on the button and watch the image for about 15 sec.

How and what do you feel?

Now you can klick the image away by klicking on it once again.

Isn’t it amazing that only a few features are necessary to evoke an emotion or a feeling in us? The recent “evolution” of the emoji is living proof that we are incredibly skilled in picking up an emotional expression. But how are feelings transmitted or induced by just watching another human face or the minimalistic sketch of it? Watching another person’s emotions induces the same feelings in ourselves and this is how we can understand how others feel. This mechanism is the bases of empathy.

 
What is incredibly interesting is that we are not only skilled in understanding human emotional expressions, we also “understand” the emotions of many other species, especially mammals. This skill has had a high evolutionary advantage: You don’t want to stay near a saber-toothed-Tiger when he/she is in a bad mood and/or hungry! Thus, as already Darwin points out, especially the avoidance of aggression intra- as well as between species has a high evolutionary advantage and constitutes a major benefit for survival. If this is true for us, the human primate, then it is most likely a capability that most animals possess. 

That this is true and goes even beyond the ability to identify aggression, has been shown for dogs. Dogs are, at least in Eurasia and Africa, the first animals that were domesticated and humans and dogs share many millenia of close partnership, if not symbiosis. Thus, it may not be surprising, that dogs are really good in reading and interpreting human emotional facial expressions.

But what about horses? Horses, as flight animals, are much more different from humans than dogs are. Dogs are, like humans, predators. Nonetheless, all three species are very social and live in groups, which makes them apt to attend to social signals. Who ever has observed a herd of horses over a period of time will be impressed how subtle and differentiated their communication is. Especially, because horses, as flight animals, almost never use sounds to communicate. The non-vocal “chitchat” in a herd is just amazing! 

But can horses read human facial emotional expressions just like dogs can? All scientific evidence available suggest, they can!

Karen McComb and co-workers were the first to systematically investigate the reactions of horses in response to human facial expressions. In a first study (Smith et al., 2016) the authors exposed 28 horses to photographs of human happy and angry faces. A happy face was defined as presenting a positive human emotional expression, while an angry face was expected to represent a negative human emotional expression. Like dogs, horses reacted with specific behavioral responses and a faster increase in heart rate to the pictures of a human angry face compared to the happy face. According to the authors, their study represents the first evidence of horses’ abilities to spontaneously discriminate between positive and negative human facial expressions in photographs. In addition to the behavioral response, their study was the first to show a specific heart rate response to heterospecific (in this case human) facial expressions of emotion. Heart rate is an important indicator for the physiological state of activation and an increase in heart rate is often used as an indicator for a stress response.

This finding is principally interesting as it shows that horses are in fact able to discriminate human angry and happy faces on photographs, and that they show behavioral and physiological reactions indicating a slight stress response when seeing a human angry face. But how relevant is this response with respect to future interactions with the particular human, whose face the horses saw? 

In a second study conducted in 48 horses by the same group (Proops et al., 2018), the experimenters presented the horses with a photograph of an angry or happy human face of a particular person. Several hours later, the horses were exposed to the same person with a neutral expression. Even though the exposure to the happy or angry face was very brief, the horses showed different behavioral responses to the corresponding person in a neutral state, depending on whether they had seen a picture of a happy or an angry face of that very same person before. The horses did not show these reactions to a person, they had not seen on a photograph before. In addition, the persons themselves did not know, what version of the photography (happy vs. angry) the horses had seen before while performing the neutral encounter.

The authors state “…that, like humans, horses remember past expressions seen on the faces of particular people and use this emotional memory to guide future interactions. Their response is more negative if they previously saw an angry versus a happy photo of the person, and this memory is specific to the person whose face they saw…”. 

In conclusion, these studies show that horses can very well discriminate positive (a smile) and negative (here “angry” indicating aggression) human faces, even though the faces were only presented as photographs. Moreover, the emotion they picked up from these pictures had a behavioral as well as physiological impact on their future interaction with this particular human.

As if that was not enough, a study from Léa Lansades group (Trösch et al., 2020) suggests, that horses even react to positive and negative interactions they observed in a video. In their study, the investigators showed horses videos with either a positive (grooming) or negative (a medical treatment) interaction of an unfamiliar (“actor”) horse with an unknown experimenter. The horses reacted emotionally while watching the videos, expressing behavioral (facial expressions and contact-seeking behavior) and physiological (heart rate) cues of positive emotions while watching the positive video, and of negative emotions while watching the negative video. Thus, the horses clearly perceived and understood the actions shown in the video and showed a corresponding emotional reaction to it. After the videos, the horses were exposed to the experimenters from the videos (positiv vs. negative) in a choice test and the results showed a clear distinction between the two experimenters.

Thus, the horses transferred the information of the videos showing an actor horse to their own situation. In scientific terms, this ability, namely to gather information by observing third party interactions, is called “eavesdropping”. Even though not frequently investigated, studies show that animals can indirectly gather meaningful information about other individuals by eavesdropping on their third-party interactions. Trösch et al. (2020) confirmed with their study, that horses are very well capable to use this information to guide their future actions. We need to keep in mind, that these data also show, that this behavioral reaction is associated with emotions on the part of the horse.

I find these results mind blowing! Of course, probably like everyone else who owns or handles horses, I am amazed about their intelligence and likewise about their sensitivity. However, what these results suggest is, that horses are capable to monitor our emotional state just by watching our facial expressions (they can also smell emotions, but that is a different topic). In addition, they show a corresponding emotional reaction to what we express. The consequences of these results are quite dramatic: Any emotion we take with us to the stable will transfer to the horse we handle. Moreover, even if a horse just watches a positive or negative interaction with a human, this will have consequences for future interactions with this particular human. 

Surely, all of us Equestrians are aware that we should probably not attempt to handle or ride horses, if we are in a bad mood or otherwise distracted. However, to learn about the psychobiological mechanism of this has made the whole issue more real to me. If I am honest, we should not be surprised by the astounding emotional intelligence of horses, be it within their own species, or cross-species such as with us humans. A creature who is so apt to respond to the most subtle visual signal in the herd, such as the twitch of an ear, the blink of an eye, is prown to be most sensitive to visual signals like our facial expressions. In particular when these signals are of high socio-emotional relevance, such as the horsehuman interaction must be for a horse in our care. 

I am not sure, whether horses can find out, if and when we are cheating. It is something humans are well capable of, but horses don’t do - their brain is simply not constructed in a way that would allow them to cheat. I would still try to smile and have a positive, caring, and friendly interaction, even though I might actually not feel like smiling. Nevertheless, research also shows that when we smile, our facial expression will impact our mood and even, if we didn’t feel like it in the first place, a smile on our face will make us happier than we were before. And if my happy face leads to a positive encounter with my horse, there is a pretty good chance that my somewhat “forced” smile may turn into a real one!

Emotions are powerful! They guide more of our doings than we “rational” and ever so cognitive humans are willing to admit. If you doubt that, then go back to the little experiment from the beginning… And if I were to give a recommendation, use the happy face! 😊

References:
Trösch M, Pellon S, Cuzol F, Parias C, Nowak R, Calandreau L, Lansade L. Horses feel emotions when they watch positive and negative horse-human interactions in a video and transpose what they saw to real life. Anim Cogn. 2020 Jul;23(4):643-653. doi: 10.1007/s10071-020-01369-0. Epub 2020 Mar 11. PMID: 32162112 

Proops L, Grounds K, Smith AV, McComb K. Animals Remember Previous Facial Expressions that Specific Humans Have Exhibited. Curr Biol. 2018 May 7;28(9):1428-1432.e4. doi: 10.1016/j.cub.2018.03.035. Epub 2018 Apr 26. PMID: 29706519 

Smith AV, Proops L, Grounds K, Wathan J, McComb K. Functionally relevant responses to human facial expressions of emotion in the domestic horse (Equus caballus). Biol Lett. 2016 Feb;12(2):20150907. doi: 10.1098/rsbl.2015.0907. PMID: 26864784 Free PMC article. 

Charles Darwin: The expression of the emotions in man and animals. London: John Murray, Albemarble Street, 1872. 

darwin-online.org.uk/content/frameset?itemID=F1142&viewtype=side&pageseq=1