Thursday, December 15, 2011

Trustworthiness and the cortico-facial complex

My paper entitled "Face to face with the social brain" will appear in a forthcoming issue of Philosophical Transactions B. Here is the abstract:

Recent comparative evidence suggests that anthropoid primates are the only vertebrates to exhibit a quantitative relationship between relative brain size and social group size. In this paper, I attempt to explain this pattern with regard to facial expressivity and social bonding. I hypothesize that facial motor control increases as a secondary consequence of neocortical expansion due to cortical innervation of the facial motor nucleus. This is supported by new analyses demonstrating correlated evolution between relative neocortex size and relative facial nucleus size. I also hypothesize that increased facial motor control correlates with enhanced emotional expressivity, which provides the opportunity for individuals to better gauge the trustworthiness of group members. This is supported by previous evidence from human psychology, as well as new analyses demonstrating a positive relationship between allogrooming and facial nucleus volume. I suggest new approaches to the study of primate facial expressivity in light of these hypotheses.

UPDATE 5/29/12: This paper appears in the July 2012 issue (subscription required until July 2013). Email me for a PDF (seth dot dobson at dartmouth dot edu).

Social uncertainty promotes emotional expressivity

My paper entitled "Coevolution of facial expression and social tolerance in macaques" will be published in an upcoming issue of American Journal of Primatology. Here is the abstract:

The purpose of this study is to test the hypothesis that social tolerance drives the evolution of facial expression in macaques. Macaque species exhibit a range of social styles that reflect a continuum of social tolerance. Social interactions in more tolerant taxa tend to be less constrained by rank and kinship than in less tolerant macaques. I predicted that macaques that are more tolerant would exhibit a wider range of facial displays than less tolerant species because interactions that are open to negotiation are characterized by greater uncertainty than interactions that are constrained by rank or kinship. To test this hypothesis, I conducted a phylogenetically informed regression analysis (N = 11) using previously published data on repertoire size and two quantitative measures of social tolerance (conciliatory tendency and counter-aggression). As predicted, macaques with more tolerant social styles tended to have larger repertoires than less tolerant species. These results support the hypothesis that increased social tolerance favors the elaboration of communication to mitigate uncertainty.

UPDATE 2/2/12: This paper appears in the March 2012 issue (subscription required). Email me for a PDF (seth dot dobson at dartmouth dot edu).