Tuesday, June 8, 2010

Dartmouth Now story

Kelly Seaman has written a series highlighting Dartmouth faculty field work experiences on the Dartmouth Now website. Click here to see her story about my work in Ethiopia with gelada monkeys.

Monday, June 7, 2010

Face to face with the social brain

Just got an article entitled "Correlated evolution of brain regions involved in producing and processing facial expressions in anthropoid primates" accepted in Biology Letters (co-authored with Chet Sherwood). Here's the abstract:

Anthropoid primates are distinguished from other mammals by having relatively large primary visual cortices (V1) and complex facial expressions. We present a comparative test of the hypothesis that facial expression processing co-evolved with the expansion of V1 in anthropoids. Previously published data were analyzed using phylogenetic comparative methods. The results of our study suggest a pattern of correlated evolution linking social group size, facial motor control, and cortical visual processing in catarrhines, but not platyrrhines. Catarrhines that live in relatively large social groups tended to have relatively large facial motor nuclei, and relatively large primary visual cortices. We conclude that catarrhine brains are adapted for producing and processing complex facial displays.
*UPDATE (6/30/10): The publisher's version is online here (subscription required until 2/23/12). Contact me if you want a PDF.

Friday, June 4, 2010

Sunday, May 9, 2010

The adaptive chin revisited

I have a paper in press at the American Journal of Physical Anthropology which I co-authored with Zaneta Thayer. The article is entitled "Sexual Dimorphism in Chin Shape: Implications for Adaptive Hypotheses." Here's the abstract:

The chin, or mentum osseum, is one of the most distinctive anatomical traits of modern humans. A variety of hypotheses for the adaptive value of the chin have been proposed, ranging from mechanical stress resistance to sexual selection via mate choice. While the sexual selection hypothesis predicts dimorphism in chin shape, most biomechanical hypotheses preclude it. Therefore determining the presence or absence of significant sexual dimorphism in chin shape provides a useful method for differentiating between various adaptive hypotheses; however, this has yet to be done due to a lack of quantitative data on chin shape. The goals of this study are therefore: (1) to introduce a new method for quantifying chin shape and (2) to determine the presence or absence of sexual dimorphism in chin shape in a diverse sample of modern humans. Samples were drawn from recent human skeletal collections representing nine geographic regions. Outlines of mentum osseum contours were quantified using elliptical Fourier function analysis (EFFA). Fourier coefficients were analyzed using principal components analysis (PCA). Sexual dimorphism in chin shape was assessed using PC loadings in the pooled geographic sample, and statistically significant differences were found. These findings provide the first quantitative, morphologically based evidence in support of adaptive hypotheses that predict dimorphism in chin shape, including the sexual selection hypothesis.

*UPDATE (6/1/10): the publisher's version is available here (subscription required).

Friday, May 7, 2010

"Smiling" is not aggressive

I wrote a letter to the editor of the American Journal of Physical Anthropology attempting to debunk the common misconception that primates show their canines to advertise aggressive intentions (i.e., I'm going to bite you). For most monkeys and apes, canine exposure is actually a peaceful signal, much like the human smile. Here's a link to the letter (subscription required).

UPDATE 6/8/12: You can now download a postprint version of this article here. And if you don't believe me check out this article from Current Anthropology by Samson and Waller (2010).

Tuesday, February 16, 2010

aapa 2010

I will present a poster at this year's Annual Meeting of the American Association of Physical Anthropologists. Here's the title: "Face to face with the social brain: correlated evolution of neocortical structure and facial expression in anthropoids."