Tuesday, June 24, 2008

Allometry of facial mobility

My paper entitled "Allometry of facial mobility in anthropoid primates: implications for the evolution of facial expression" is now in press at the American Journal of Physical Anthropology. Here's the abstract:

Body size may be an important factor influencing the evolution of facial expression in anthropoid primates due to allometric constraints on the perception of facial movements. Given this hypothesis, I tested the prediction that observed facial mobility is positively correlated with body size in a comparative sample of nonhuman anthropoids. Facial mobility, or the variety of facial movements a species can produce, was estimated using a novel application of the Facial Action Coding System (FACS). I used FACS to estimate facial mobility in 12 nonhuman anthropoid species, based on video recordings of facial activity in zoo animals. Body mass data were taken from the literature. I used phylogenetic generalized least squares (PGLS) to perform a multiple regression analysis with facial mobility as the dependent variable and two independent variables: log body mass and dummy-coded infraorder. Together, body mass and infraorder explain 92% of the variance in facial mobility. However, the partial effect of body mass is much stronger than for infraorder. The results of my study suggest that allometry is an important constraint on the evolution of facial mobility, which may limit the complexity of facial expression in smaller species. More work is needed to clarify the perceptual bases of this allometric pattern.

UPDATE (8/25/08): The publisher's version of this paper is now available online here (subscription required). Contact me if you want a PDF.

Wednesday, June 4, 2008

Gelada Fieldwork

I spent six weeks in the Simien Mountains of Ethiopia this Spring studying the social behavior and communication of gelada baboons. This is the preliminary phase of a larger project investigating the motivational contexts and social functions of facial expression in male geladas. My collaborators are Drs. Jacinta Beehner and Thore Bergman of the University of Michigan Gelada Research Project.

UPDATE (7/21/08): Picture of me in the field courtesy of Dave Pappano.

AAPA 2008

At this year's annual meeting of the American Association of Physical Anthropologists, I presented on the allometry of facial mobility in a symposium focusing on the muscles of facial expression. The symposium was organized by Karen Schmidt and Anne Burrows. Here's the description:

The State of the Face: An Evolutionary Update on the Muscles of Facial Expression
The structure and function of the face have long been of interest to biological anthropologists because of its pivotal role in behavioral, cognitive, and sensory adaptations. The evolution of the muscles of facial expression specifically, however, has been relatively neglected in primate and human evolutionary studies despite the role of these muscles in nonverbal communication as well as in articulatory movements of speech, audition, olfaction, tactile exploration, and social interaction. The goal of this symposium is to draw together researchers currently studying the evolution of the muscles of facial expression from comparative, developmental, histological, anatomical, and behavioral perspectives to update the biological anthropological understanding of the face. A secondary goal is to identify novel evolutionary interpretations of the structure and function of the muscles of facial expression, in both human and nonhuman primates. The role of adaptational processes in the development of species-specific features of the facial musculature will be addressed. Recent work in nonhuman primates as well as in humans will be incorporated. We also aim to identify new avenues of understanding the face that incorporate both communicative and noncommunicative functions of the muscles of facial expression and closely associated structures.

Some of the other presenters included Lisa Parr and Bridget Waller of the ChimpFACS project.