When observing chimpanzees, people often notice facial expressions that seem similar to a human smile. This resemblance can lead to interpreting their behaviors through a human perspective, a phenomenon known as anthropomorphism. However, these expressions are frequently misunderstood. Their facial signals serve distinct purposes within their social structures and often convey meanings quite different from what a human smile implies. Understanding these expressions requires looking beyond superficial similarities to grasp their true communicative functions.
Chimpanzee Facial Expressions
Chimpanzees exhibit a range of facial expressions, two commonly mistaken for human smiles: the bared-teeth grimace and the play face. The bared-teeth grimace involves pulling the lips back tightly to expose both upper and lower teeth. This expression often occurs alongside a low body posture or a cowering stance, making the teeth highly visible. It is a tense facial display that can appear similar to a wide human grin.
Another distinct expression is the play face. A chimpanzee displaying a play face will have an open mouth and a relaxed jaw. This expression may reveal the bottom row of teeth, but typically the top teeth remain covered by the lips. The play face is often accompanied by soft, breathy panting sounds, akin to human laughter.
The Purpose of Chimp Expressions
Chimpanzee facial expressions play an important role in their social interactions, conveying specific messages. The bared-teeth grimace is primarily a signal of fear, anxiety, or submission. A chimpanzee uses this expression to show deference to a dominant individual or to de-escalate a potentially tense situation. It serves as a visual signal within their society, indicating that the individual is not a threat and seeks to avoid conflict.
The play face signals an invitation to engage in playful interactions. This expression communicates a non-aggressive intent during activities such as rough-and-tumble play. It assures other chimpanzees that the interaction is friendly and not a real threat, even when the play involves mock aggression. Play faces are observed during social play, coordinating and sustaining these interactions.
Distinguishing Chimp and Human Smiles
While superficially similar, chimpanzee facial expressions and human smiles differ fundamentally in their origins and communicative functions. Human smiles are primarily associated with positive emotions such as joy, amusement, and social bonding. They can be voluntary and are used to convey happiness or to facilitate friendly social interactions. The human smile has evolved to serve diverse social roles, including putting others at ease or showing affection.
Chimpanzee expressions, however, stem from different emotional states and serve distinct communication purposes within their species. The bared-teeth grimace, for instance, signals fear, stress, or a desire to appease, not happiness. The play face indicates a desire for playful interaction, rooted in a specific social context rather than broad positive emotion. Anthropomorphizing chimpanzee behavior, assuming their “smile” means human-like happiness or friendliness, can lead to misinterpretations, particularly when humans interact with chimpanzees.