Primate Faces and Facial Expressions - )

Social Research, Spring, 2000 by Signe Preuschoft

There is no perfect solution to this, but it should be noted that, talking about non-humans, things can become quite confusing if an author just uses a term borrowed from the human repertoire (e.g., "grimace"), without stating precisely what the display looks like, or what its social function is.

Understanding Primate Facial Displays

Facial displays are evolutionarily designed devices to elicit a response from the receiver (Tinbergen, 1952; Dawkins and Krebs, 1978). They function as an appeal to the receiver as long as the receiver knows how to decipher the conveyed message. For communication to work there has to be a regular correspondence between the message expressed by a display and the meaning attached to it.

A. The Message-Meaning Analysis

The social function of a display is defined by its message and its meaning. The message is what the sender expresses by the display. The meaning corresponds to the interpretation of the display by the receiver (cf. Smith, 1965).(1) A display's social function can be understood from the behavioral context in which it is performed. The message can be derived from its embedding in other behaviors shown by the sender. The display's embedding in behaviors shown to the receiver elucidates its meaning. To ensure that they record all relevant behaviors, ethologists focus their attention on one individual, and its interaction partners. All actions of the `focal animal' as well as those of its partners are recorded continuously. For each display, all behaviors performed by the sender before, during and after the display are noted. A corresponding record is kept of the behaviors performed by the receiver before, during and after the sender performed the display. The subsequent analysis of these behavioral sequences aims to capture the changes in behavior that are contingent on the display. For instance, two Tonkean macaques, Cathie and Beattie sit together:

   Cathie attempts to touch Beattie's infant, but then flinches and peers at
   Beattie. She scratches, looks around and yawns. Beattie then looks at
   Cathie and starts a lip-smacking display. Cathie glances at Beattie, then
   she moves closer and starts grooming Beattie's arm and shoulder. After
   several minutes of grooming Beattie's infant reaches for Cathie and they
   start playing (personal observation).

If this is a typical sequence, the quantitative analysis will reveal evidence that individuals are uneasy (flinch, scratch, yawn) immediately before receiving a lip-smacking display than afterwards. A result like this allows us to conclude that, in Tonkean macaques, lip-smacking can serve a reassuring function: The sender, Beattie, expresses her tolerance and friendly intentions to the insecure receiver, Cathie. To Cathie, the lip-smacking means that she is encouraged to stay on and interact in socio-positive fashion.

Obviously, ethologists "gauge" their understanding of non-human facial expressions in accordance with the behavior of the interacting individuals. Understanding primate behavior is essentially a problem of translation. Due to common laws of physics and a shared evolutionary past, there are fortunately a couple of "archimedic points." We can immediately recognize the meaning of such behaviors as hitting, biting, fleeing, embracing, gentle touching, cradling--these behaviors form something like a kinetic inter-species Esperanto. Using statistical procedures, ethologists determine the contingencies between a facial display and other behaviors, the function of which is easier to comprehend.