Check out Smithsonian Magazine’s recent article about geladas.

I just got my 150th anniversary edition of Origin for free with a special introduction by Ray Comfort. I’m glad my university among the best at brainwashing young minds with the atheistic, racist, and thoroughly debunked theory of evolution by means of natural selection. Please note the sarcasm.

The upcoming special issue of International Journal of Primatology includes a number of interesting articles on the function of primate coloration in species such as geladas (Theropithecus gelada) (Bergman et al., in press), drills (Mandrillus leucophaeus) (Marty et al., in press), mandrills (M. sphinx) (Setchell et al., in press), and red-fronted lemurs (Eulemur fulvus rufus) (Clough et al., in press). While most mammals are rather drab in color, some primates (especially primate males) are quite colorful. Indeed, sexual dimorphism and variation among males in coloration suggests that the bright colors of male primates may be sexually selected signals. Male coloration may be a ‘badge of status’, indicating rank or status to other males; or it may convey information to females about underlying male ‘quality’. In the latter, these color-based signals need to incur some cost to a male (usually physiological) in order to be kept honest. This keeps ‘low-quality’ males from advertising a ‘high-quality’ signal, thus maintaining a strong correlation between signal strength/intensity (bright coloration) and male quality. Females then discriminate among males based on this signal.

While many of the articles have been available online (not open-access sadly) for some time now, the drill article (Marty et al., in press)was just released yesterday. I have been waiting for this publication for some time, since drills are among my favorite primates (and dream post-doc/future research endeavor). Drills exhibit the highest degree in sexual size dimorphism among primates (males nearly 3x the size of females). Male also possess brightly colored patches of skin on the lip, groin, and rump (see picture below). Marty and colleagues (2009) revealed that male drill coloration is associated with social dominance rank and predicts sexual activity with female drills. However for males of a given rank, coloration was found to be unrelated to sexual activity and association patterns with female drills (Marty et al., in press). In other words, male drill coloration appears to indicate status or social dominance rank and is not (directly) related to female mate preference (Marty et al., in press).

Check out this male drill from Fig 1 in  (Marty et al., in press)

References

Bergman, T. J., Ho, L., & Beehner, J. C. (In press). Chest color and social status in male geladas (theropithecus gelada). International Journal of Primatology.

Clough, D., Heistermann, M., & Kappeler, P. M. (In press). Individual facial coloration in male eulemur fulvus rufus: A condition-dependent ornament? . International Journal of Primatology.

Marty, J. S., Higham, J. P., Gadsby, E. L., & Ross, C. (In press). Dominance, coloration, and social and sexual behavior in male drills mandrillus leucophaeus . International Journal of Primatology.

Setchell, J. M., Charpentier, M. J. E., Abbott, K. M., Wickings, E. J., & Knapp, L. A. (In press). Is brightest the best? Testing the hamilton-zuk hypothesis in mandrills. International Journal of Primatology.

Yawning is a common phenomenon among vertebrates. Despite its widespread occurrence, the function of yawning remains a mystery ¹. Indeed, yawning has been suggested as (i) a cooling mechanism for the brain to maintain cognitive function; (ii) a communicative behavior to indicate drowsiness or stress; (iii) a way to maintain vigilance/promote alertness among animals ². Furthermore, contagious yawning (when observing, thinking, and/or hearing yawning induces yawning behavior in another individual) has been linked to individual differences in theory of mind tasks and self-facial recognition among humans ¹. This research suggests that the yawning contagion is associated with the ability to attribute mental states to others (and possibly empathy). Among non-human mammals, contagious yawning has been demonstrated in chimpanzees (Pan troglodytes), stump-tailed macaques (Macaca arctoides), and domestic dogs (Canis familiaris) ^2-5.

Recent research published in PNAS demonstrates that my study species—the gelada baboon (Theropithecus gelada)—exhibits contagious yawning². Perhaps even more interesting, the researchers demonstrate that the strength of social relationships (not spatial proximity) is correlated with the contagiousness of yawning (i.e. more two individuals groomed, the more likely there were to respond to each other’s yawn)². Females matched yawning types (covered teeth, uncovered teeth, and uncovered gums) more often than males; and yawning contagion was unrelated to stressful events².

Despite these findings, several questions remain. First, I am dubious of the team’s data analysis. To determine whether or not yawning is contagious in geladas, the researchers compared a test condition (frequency of yawning for animal X given animal Y yawns) with a control condition (frequency of yawning for animal X in absence of yawning stimulus by another animal) ². This analysis ignores the non-responsiveness of animals that are equally exposed to the yawning stimulus of animal Y. Additionally, humans are the only species where a link between mental state attribution and sensitivity to the yawning contagion is demonstrated ¹. If one behavior (contagious yawning) is found in another species, this does not (by default) imply that that species is capable of mental state attribution and/or empathy. Indeed, the function of a yawning contagion may not a building block of full-blown empathy, but instead part of a different system of social behavior.

Regardless, these findings are certainly interesting. Gelada social relationships and (especially) social cognition remain understudied. However, I’m pretty sure we’ll be learning much more about our ‘bleeding-heart’ friends in the coming months.

1.   Platek, S. M., Critton, S. R., Myers, T. E. & Gallup, G. G. Contagious yawning: the role of self-awareness and mental state attribution. Cognitive Brain Research 17, 223-227 (2003).

2.   Palagi, E., Leone, A., Mancini, G. & Ferrari, P. F. Contagious yawning in gelada baboons as a possible expression of empathy. Proc Natl Acad Sci U S A (2009).

3.   Anderson, J. R., Myowa-Yamakoshi, M. & Matsuzawa, T. Contagious yawning in chimpanzees. Proc Biol Sci 271 Suppl 6, S468-S470 (2004).

4.   Joly-Mascheroni, R. M., Senju, A. & Shepherd, A. J. Dogs catch human yawns. Biol Lett 4, 446-448 (2008).

5.   Paukner, A. & Anderson, J. R. Video-induced yawning in stumptail macaques (Macaca arctoides). Biol Lett 2, 36-38 (2006).

After near fifteen years of waiting, the partial skeleton of Ardipithecus ramidus is published this week in Science. “Ardi” is a 4.4 million year old hominin from the Aramis region of Ethiopia and is the oldest partial hominin skeleton discovered to date. There are 11 publications in this week’s Science covering all things Ardipithecus. Here is a shot of the skeleton on the cover.

For better blog coverage, please check out more paleoanthropologically inclined blogs such as:

John Hawk’s weblog

Lawn Chair Anthropology