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Reverse Dissection and DiceCT Reveal Otherwise Hidden Data in the Evolution of the Primate Face
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Classifying chimpanzee facial expressions using muscle action.

Lisa A Parr1, Bridget M Waller, Sarah J Vick

  • 1Yerkes National Primate Research Center, Atlanta, GA 30329, US. parr@rmy.emory.edu

Emotion (Washington, D.C.)
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Summary

The Chimpanzee Facial Action Coding System (ChimpFACS) validates most existing chimpanzee facial expressions. This research identifies unique muscle movements for expressions, suggesting structural homologies with human facial expressions.

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Area of Science:

  • Primatology
  • Comparative Psychology
  • Evolutionary Biology

Background:

  • The Chimpanzee Facial Action Coding System (ChimpFACS) is an objective tool for measuring chimpanzee facial movements.
  • ChimpFACS is based on the human Facial Action Coding System (FACS), enabling structural comparisons of facial expressions.
  • Facial expressions are crucial for understanding social and emotional communication in primates.

Purpose of the Study:

  • To validate existing categories of chimpanzee facial expressions using ChimpFACS.
  • To identify prototypical facial movement configurations in chimpanzees.
  • To explore potential structural homologies between chimpanzee and human facial expressions.

Main Methods:

  • Application of the ChimpFACS to chimpanzee facial behavior.
  • Discriminant function analyses to validate expression categories.
  • Identification and illustration of peak intensity prototypical expression configurations.

Main Results:

  • ChimpFACS successfully validated 6 out of 9 existing chimpanzee facial expression categories.
  • Potential issues with ChimpFACS or existing categorizations were discussed for unvalidated categories.
  • Unique combinations of muscle movements were identified for validated expressions, forming prototypical configurations.

Conclusions:

  • The study provides empirical validation for most chimpanzee facial expression categories using ChimpFACS.
  • Prototypical facial movement configurations offer insights into the structural basis of chimpanzee expressions.
  • Findings suggest potential structural homologies between chimpanzee and human facial expressions, advancing the study of emotional communication evolution.