To understand the evolution of emotional communication, comparative research on facial expression similarities between humans and related species is essential. Facial expressions are critically important for coordinating social interaction, facilitating group cohesion and maintaining individual social relationships.
As our very distant cousins, it’s easy to see how monkeys are a lot like humans … even if we did manage to come up with iPhones and get ourselves to the moon. So alike are humans and non-human primates that it’s pretty easy to anthropomorphize and think we know what’s going on in those monkey brains.
All too often, wildlife tourists mistake w.ar.ning signs and ag.gr.ess.ion in macaques as smiles or kisses – which leads to ʙɪᴛᴇs of humans and ᴡᴇʟғᴀʀᴇ ᴡᴏᴇs for the primates. However, some facial expressions have been shown to differ in meaning between humans and nonhuman primates like macaques. This ambiguity in signalling emotion can lead to an increased r.i.s.k of a.gg.re.ss.ion and ɪɴᴊᴜʀies for both humans and animals. This raises sᴇʀɪᴏᴜs concerns for activities such as wildlife tourism where humans closely interact with wild animals.
The group of behavioral ecologists and psychologists, led by Laëtitia Maréchal, begin their paper by explaining the “universality hypothesis” that says the basic emotions of anger, ᴅɪsɢᴜsᴛ, ғᴇᴀʀ, happiness, sᴀᴅness, and surprise should be expressed in similar ways between humans and nonhuman primates.
The team worked with three groups of participants – each group with varying degrees of experience with macaques – who were quizzed with photos of the monkey’s facial expressions. In the end, they found that all participants made mistakes confusing ᴀɢɢʀᴇssɪᴠᴇ faces with docile, neutral and friendly faces. Not surprisingly, the most experienced group made the least mistakes, but still mistakes were made – experts made 20.2% mistakes in interpreting ᴀɢɢʀᴇssɪᴠᴇ facial expressions.
“There is a growing interest in wildlife tourism, and in particular primate tourism. People travel to encounter wild animals, many of them attempting to closely interact with monkeys, even though this is often prohiʙɪᴛᴇd,” Maréchal says. “However, sᴇʀɪᴏᴜs concerns have been raised related to the safety of the tourists interacting with wild animals. Indeed, recent reports estimate that monkey ʙɪᴛᴇs are the second cause of ɪɴᴊᴜʀy by animals after dogs in South East Asia, and ʙɪᴛᴇs are one of the main vectors of ᴅɪsᴇᴀsᴇ tra.ns.mission between humans and animals.”
“Our findings indicate that people who are inexperienced in macaque behaviour have difficulties in recognising monkey’s emotions, which can lead to ᴅᴀɴɢᴇʀᴏᴜs situations where they think the monkeys are happy but instead they are ᴛʜʀᴇᴀᴛening them.”
Examples of macaques’ various facial expressions
- Neutral expression
Resting facial expression, shown in calm social contexts or when resting alone. All other expressions differ from this standard facial display.
- Affiliate expressions
Affiliate facial expressions are often performed together with submissive and ᴀɴxɪᴏᴜs or ғᴇᴀʀful expressions, depending on the context. The mouth is half open and the lips slightly protruded. This expression involves a chewing movement and clicking or smacking of the tongue and lips.
- Submissive expressions
The corners of the lips are fully retracted and the upper and lower teeth are shown.
- ᴅɪsᴛʀᴇssed expressions
The mouth is widely open, and the animal is yawning. Yawning can be related to ᴅɪsᴛʀᴇss and ᴀɴxɪᴇᴛʏ in primates.
- ᴛʜʀᴇᴀᴛ expressions
The eyebrows are raised, the animal stares intently and the lips are protruded to form a round mouth.
- ᴀɢɢʀᴇssɪᴠᴇ expressions
The eyebrows are raised, the animal stares intently and the mouth is open showing the teeth.
The authors discuss measures to help reduce misinterpreting the monkeys’ moods, like keeping a safe distance between tourists and wild animals, lessons and videos, supervised visits with expert guides. “If we can educate people, and prevent monkey ʙɪᴛᴇs, we can not only reduce the r.i.s.k of ᴅɪsᴇᴀsᴇ i.nf.e.ction, we can improve on the tourism experience,” note the researchers. “These findings are highly relevant to the general public and any professional in wildlife tourism, where wild animals can interact with the general public.”