Wednesday, June 6, 2012

Facial display complexity in geladas

Stefanie Lazow '12 recently completed a senior honors thesis in anthropology. Her project is the first systematic investigation of facial display structure and motivation in wild geladas (abstract below). Stefanie will begin medical school next year at Weill Cornell Medical College in New York.

My thesis explores mechanisms for the generation of communicative complexity within the facial display repertoire of the gelada baboon (Theropithecus gelada). Firstly, this project provides a systematic investigation of the unique lip-flip movement of the gelada baboon in order to explore the relationship between facial mobility and communicative complexity in primate facial communication systems. I applied the Facial Action Coding System (FACS) to facial events present in video footage of social interactions between wild geladas. In order to determine the role of the lip-flip, I clearly defined the structure of displays containing a lip-flip movement and inferred the lip-flip’s motivational basis from associated sender behaviors. I found that the lip-flip is an optional expression element in the non-aggressive and mostly submissive gelada bared-teeth display, and appears to add signaling information about benign intent during or after an approach. My conclusions about the possible communicative roles of the lip-flip movement as a specifier, intensifier, and/or alerting component suggest that there are various ways that increased facial mobility can facilitate the generation of communicative complexity within primate communication systems. Secondly, I present evidence of the blending of facial displays within the gelada repertoire, and discuss how the capacity for display blending might contribute to the diversification of possible signals within a communication system. Thirdly, I report sex differences in the gelada facial expression communication system, which suggest that social pressures influence the development of communicative complexity. My study has implications not only for the study of primate facial expressions, but also for the fields of animal communication and human language more broadly.

High facial mobility in a solitary primate?

My undergraduate research assistants Michelle Evans '13, Tina Ma '14, and Holly Wakeman '14 recently presented a poster on orangutan facial mobility at the Karen E. Wetterhan Science Symposium. Michelle is planning on expanding this project into a senior honors thesis in anthropology.

Click here to view and/or download the poster for free on figshare.

For further information on orangutan facial movements see Bridget Waller's OrangFACS website.

Tuesday, January 17, 2012

The Hominid Hunting blog on has recently highlighted my work on the chin with Zane Thayer (Dartmouth '08).

Why do humans have chins?

Friday, January 6, 2012

AAPA Portland 2012

I will be presenting a poster entitled "Co-evolution of facial expressivity and cooperation in catarrhine primates" at the 2012 meeting of the American Association of Physical Anthropologists in Portland, OR. Here is the abstract:

Psychologists have suggested that facial expressivity is signal of trustworthiness in humans. This is based on the observation that people are more likely to cooperate with individuals that readily produce facial displays. The “trustworthy face hypothesis” implies that facial expressivity evolved in correlation with cooperative behaviors. To test this hypothesis in catarrhines, I examined the co-evolution of facial motor control and social grooming, which is an example of reciprocal altruism. Data were gathered from the literature (N = 10) and analyzed using phylogenetic GLS regression. The dependent variable was facial nucleus volume, which is a proxy for facial motor control. Medulla volume, social grooming time, and population group size were predictors. Social grooming time was a significant predictor of facial nucleus volume independent of medulla volume (b = 0.21, t = 2.65, p < 0.05). In contrast, the effect of group size on facial nucleus volume did not reach statistical significance after controlling for medulla volume (b = 0.14, t = 1.74, p = 0.07). When both social grooming time and group size were included as predictors in the same model, neither variable reached statistical significance, but the effect of grooming time was stronger than group size (social grooming: b = 0.22, t= 1.55, p =0.18; group size: b = -0.01, t = -0.08, p = 0.94). The results of this study provide comparative support for the trustworthy face hypothesis. The importance of facial expressivity in cooperative interactions might be a productive area of future research in behavioral primatology.

Red scare

Dartmouth Alumni Magazine has published a short blurb about my work with Jerald Kralik and his students on the psychological effects of red coloration in competitive contexts.