Seth Dobson - Dartmouth College

Smithsonian.com

2012-01-17T11:13:00.000-05:00

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

Why do humans have chins?

AAPA Portland 2012

2012-01-06T13:41:00.002-05:00

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.

Dartmouth Alumni Magazine

2012-01-06T13:35:00.001-05:00

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.

Forthcoming paper in Phil Trans B

2011-12-15T09:28:00.000-05:00

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.

Upcoming article in AJP

2011-12-15T09:22:00.000-05:00

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 2/2/11: This paper appears in the March 2012 issue (subscription required). Email me for a PDF (seth dot dobson at dartmouth dot edu).

New Psych Science article

2011-05-03T10:21:00.005-05:00

I have a new paper coming out in Psychological Science with Sara Khan, William Levine, and Jerald Kralik. The title of our brief report is: "Red signals dominance in male rhesus macaques." In the paper, we present the first experimental evidence that red signals dominance in nonhuman primates. Our results reveal that male monkeys would rather steal food from humans wearing blue or green than from humans wearing red. A similar predisposition in humans may explain the advantage conferred by wearing red in combat sports.

*UPDATE 6/9/11: The official psych science press release is now online and making the rounds on the interwebs.

*UPDATE 8/17/11: This paper appears in the August 2011 issue. Contact me for a PDF.

Behavior 2011

2011-05-03T10:06:00.006-05:00

I'm presenting at this year's joint meeting of the Animal Behavior Society and the International Ethological Conference as part of a symposium entitled "Does social complexity influence communicative complexity?" My talk is entitled "Does social complexity drive the evolution of primate facial expression?" The symposium is organized by Todd M. Freeberg, Indrikis Krams, and Cecilia Kullberg.

*UPDATE 5/29/11: This symposium will be associated with a special issue of Philosophical Transactions of the Royal Society B scheduled for mid-2012 release.

The brain mosaic

2011-04-11T19:10:00.008-05:00

I have a new paper coming out entitled "Mosaic evolution of brainstem motor nuclei in catarrhine primates." The paper is coauthored with Chet Sherwood and will appear in a special issue of the new open access journal Anatomy Research International. Here's the abstract:

Facial motor nucleus volume co-evolves with both social group size and primary visual cortex volume in catarrhine primates as part of a specialized neuroethological system for communication using facial expressions. Here we examine whether facial nucleus volume also co-evolves with functionally unrelated brainstem motor nuclei (trigeminal motor and hypoglossal) due to developmental constraints. Using phylogenetically informed multiple regression analyses of previously published brain component data, we demonstrate that facial nucleus volume is not correlated with the volume of other motor nuclei after controlling for medulla volume. Our results show that brainstem motor nuclei can evolve independently of other developmentally linked structures in association with specific behavioral ecological conditions. This finding provides additional support for the mosaic view of brain evolution.

The title of the special issue is New models and insights into primate evolutionary morphology. The editors are Anne Burrows, Kathleen Muldoon and Adam Sylvester.

*UPDATE 4/18/11: Click here to download the PDF.

2011 AnthroTree Workshop

2011-03-01T13:58:00.002-05:00

I'll be participating in a workshop on comparative methods organized by Charles Nunn. My session will focus on using COMPARE to study correlated evolution of species traits. Here's an overview of the workshop:

The second annual AnthroTree Workshop aims to make phylogenetic methods more accessible by providing hands-on experience to evolutionary anthropologists interested in learning phylogenetic comparative methods.

The four-day course will feature instructors from around the world, and will cover introductions to a wide array of topics, including:

Inferring and interpreting phylogenetic trees

Studying correlated evolution using independent contrasts and PGLS

Reconstructing ancestral states
Investigating the factors that influence speciation and extinction
Computational approaches in Compare, Mesquite, R, and BayesTraits

Examples from all fields of evolutionary anthropology

In addition to lectures, worked examples and exercises, participants will bring a dataset of their choice to work on with the instructors at the workshop.

Click here for more information.

AAPA 2011 Minneapolis

2011-02-16T08:21:00.003-05:00

I will present a poster entitled "Co-evolution of facial expression and brain size: a test of the visual specialization hypothesis" at this year's annual meeting of the American Association of Physical Anthropologists. Here's the abstract:

It has been suggested that primates with more specialized visual systems tend to have relatively large brains due to selection for enlarged cortical visual processing areas. This “visual specialization hypothesis” is supported by several comparative studies. However, the behavioral bases of these co-evolutionary patterns remain unclear. If the visual specialization hypothesis is correct, then variation in visually-oriented behaviors should correlate with variation in brain size. The purpose of this study is to test this prediction by examining the co-evolution of facial expression complexity and relative brain size in extant anthropoids. Facial expression complexity is a function of facial mobility, or the number of visually distinct facial movements a species can produce. Data on facial mobility are currently available for 12 species. These data were combined with published estimates of endocranial volume and body mass. Phylogenetically-informed partial correlation analyses were used to examine the association between facial mobility and endocranial volume after controlling for body mass. Male and female data were analyzed separately. The results of this study provide broad support for the visual specialization hypothesis. Facial mobility is positively correlated with endocranial volume after controlling for body mass in males (partial r = 0.65; p = .031). However, females do not exhibit a significant partial correlation between facial mobility and endocranial volume (partial r = 0.10; p = .396). These findings suggest that male, but not female, brain size evolution is influenced by selection for facial expression processing.

This presentation is part of an invited poster symposium entitled Ears, Eyes, and Noses: Revisiting the Evolution and Ecology of the Primate Special Senses. The session is organized by Carrie Veilleux, Eva Garrett, and Rachel Jacobs.

Now taking grad students!

2011-02-01T11:07:00.001-05:00

I can now take dissertation students through the Ecology and Evolutionary Biology (EEB) graduate program at Dartmouth. I am interested in working with students on topics related to the co-evolution of social signals and sensory systems, using comparative morphological and/or behavioral approaches. That being said, any student working with me is free to develop his/her own dissertation project, as long as it's comparative.

Interested? Please contact me directly with a description of your research interests and previous experience.

Dartmouth Now story

2010-06-08T09:27:00.003-05:00

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.

Face to face with the social brain

2010-06-07T05:57:00.027-05:00

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.

An exchange between rival male geladas

2010-06-04T09:19:00.005-05:00

The adaptive chin revisited

2010-05-09T10:26:00.014-05:00

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).

"Smiling" is not aggressive

2010-05-07T14:20:00.010-05:00

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).

aapa 2010

2010-02-16T11:20:00.009-05:00

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."

AAPA 2009

2009-06-29T09:11:00.004-05:00

I presented a poster last April with my colleagues Thore Bergman and Jacinta Beehner at the Annual Meeting of the American Association of Physical Anthropologists in Chicago. The poster was entitled "The Facial Display Repertoire of Geladas."

This research was supported by the Claire Garber Goodman Fund (Dartmouth College) and the University of Michigan.

Facial mobility aids group cohesion

2008-12-02T14:51:00.011-05:00

My article entitled "Socioecological correlates of facial mobility in nonhuman anthropoids" has been accepted for publication in the American Journal of Physical Anthropology. Here's the abstract:

Facial mobility, or the variety of facial movements a species can produce, is likely influenced by selection for facial expression in diurnal anthropoids. The purpose of this study is to examine socioecological correlates of facial mobility independent of body size, focusing on social group size and arboreality as possible evolutionary agents. Group size was chosen because facial expressions are important for group cohesion, while arboreality may limit the utility of facial expressions. Data for 12 nonhuman anthropoid species were taken from previous studies and analyzed using a phylogenetic generalized least-squares approach. Regression results indicate that group size is a good predictor of facial mobility independent of body size. No statistical support was found for the hypothesis that arboreality constrains the evolution of facial mobility. The correlation between facial mobility and group size may be a consequence of selection for more effective facial expression to help manage conflicts and facilitate bonding in larger groups. These findings support the hypothesis that the ultimate function of facial expression is related to group cohesion.

*UPDATE (2/24/09): The publisher's version of this article is now online here (subscription required). Contact me if you want a PDF.

Discover Magazine Article

2008-10-21T14:00:00.003-05:00

Renowned science journalist Carl Zimmer has recently published an article on facial expression in Discover Magazine. The article describes my own research on facial mobility, as well as research by Bridget Waller and Anne Burrows.

Valley News Story

2008-09-09T08:53:00.011-05:00

My research was featured in the September 8, 2008 edition of the Valley News, a local newspaper covering the upper Connecticut river valley of Vermont/New Hampshire.

The accompanying photograph of me in the field (above) was taken by Aliza Le Roux.

IPS Edinburgh 2008

2008-08-25T10:44:00.007-05:00

I presented a paper at the 2008 meeting of the International Primatological Society entitled "Facial expression and social organization in Macaca: a phylogenetic comparative analysis." My presentation was part of a symposium on facial expression entitled "Facial expression in primates: measurement, meaning and function." Here is a description of the symposium:

Primates send and receive an array of facial signals in order to navigate their social environments, and these communicative systems have undoubtedly been influential in the evolution of both primate mind and society. Yet facial expression is a relatively understudied mode of primate communication. Several recent developments have increased our understanding of facial signals, in terms of what they communicate, how they interact with other communicative modalites and how they have evolved. In this symposium, scientists studying facial expression in primates (including humans) from a variety of different perspectives will present their theoretical positions, methodological innovations and recent findings. The overarching goals are to present the form and function of facial expressions in different species, examine different approaches in the study of facial expression, and ultimately to identify the specific role facial expressions play in the lives of primates.

The symposium was organized by Bridget Waller, Sarah-Jane Vick, and Lisa Parr. The other participants included Jan van Hooff, Karen Schmidt, Amy Pollick, Elisabetta Palagi, and Matthew Campbell.

Allometry of facial mobility

2008-06-24T09:28:00.020-05:00

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.

Gelada Fieldwork

2008-06-04T12:47:00.014-05:00

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

2008-06-04T12:11:00.003-05:00

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.

NEAA 2008

2008-03-15T16:36:00.007-05:00

I presented a paper entitled "Allometry of facial mobility in anthropoid primates" at the 2008 meeting of the Northeastern Anthropological Association in Amherst, MA. Here's the abstract:

Body size is likely to be an important constraint on the evolution of facial expression in primates. This is because facial movements are more difficult to discern in smaller species. I tested the hypothesis that 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 the human 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 performed 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 explain why smaller taxa tend to exhibit fewer facial displays than larger taxa. More work is needed to clarify the structural bases of this allometric pattern.

Some of the other folks in my session were Richard Lawler and Stacey Matarazzo.

AAPA 2007

2007-02-08T11:43:00.000-05:00

“Social Cohesion and the Evolution of Facial Expression in Nonhuman Anthropoids.” Poster to be presented at the 76th Annual Meeting of the American Association of Physical Anthropologists, Philadelphia, PA.

Abstract:

Facial displays provide information about what an individual is likely to do next. This information is essential for negotiation since the appropriate response to a facial display can inhibit aggression and/or promote affiliation. The “social cohesion hypothesis” posits that facial expression has been designed by natural selection to maintain cohesion among group members. The purpose of this paper is to test the comparative predictions of this hypothesis in diurnal anthropoids.

I used two measures of signal effectiveness: facial mobility, and published data on facial nucleus volume (N = 26). Facial mobility data were collected from video recordings of zoo animals. The facial-action coding system (FACS) was used to count the number of facial movements in each species (N = 12). Socioecological, body mass, and additional brain component data were taken from the literature. Partial effects were examined using multiple regression analyses of independent contrasts. Body mass and group size were entered as predictor variables in the facial mobility analysis. Medulla volume, group size, and grooming time were used in analyses of facial nucleus volume.

The social cohesion hypothesis is supported by the results of this study. Facial mobility is positively correlated with group size in anthropoids, controlling for size and phylogeny. Similarly, facial nucleus volume is correlated with group size and grooming time. However, these effects are only significant after excluding platyrrhines and the outlier Pongo pygmaeus. Thus, while facial expression likely evolved for the purposes of social cohesion, this particular selection pressure may have been confined to catarrhines.

Research supported by NSF (#0424160) and Sigma-Xi.