Contagious yawning in geladas

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).

Ardipithecus has arrived.

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

Synchronized exercise and endorphin release

Recent research published in Biology Letters suggests physiological mood systems may have been involved in the evolution of coordinated physical activities. Researchers from the United Kingdom discovered that the pain threshold of collegiate rowers significantly increased when exercising with teammates v. solo-exercise controls ¹. This increase in pain threshold was also observed for individuals exercising alone, however the effect was not as pronounced ¹. Since a spinal tap is necessary to measure opioids, increase in pain-threshold serves as a proxy for endogenous opioid release. For those of you who experience a ‘runners’ high’ while exercising, these endogenous opioids (endorphins) are the chemicals responsible for your state of mild euphoria. The authors suggest that this may inform our understanding of the evolution of group activities such as dancing and music-making ¹.

Here’s the figure from the paper.

P.S. Note the final author on this paper. His name is familiar to those who study geladas.

P.P.S I am back in the United States for the semester and preparing to take my qualifying examinations. Hopefully, I’ll be able to keep up Beast Ape and the Bleeding Heart Baboons in the meantime. Cheers.

REFERENCES

1.   Cohen, E. E., Ejsmond-Frey, R., Knight, N. & Dunbar, R. I. Rowers’ high: behavioural synchrony is correlated with elevated pain thresholds. Biol Lett (2009).

Lost in translation: update from SMNP

Research on wild primates is an amazing process of discovery. The monkeys act out little parts in a cosmic soap opera that serves as the background to your dissertation research. While gelada social interactions form the basis of my research, interchanges with fellow language-using primates provide much need comic relief during my time out here. For example, here is a conversation I attempted to have with my field assistant. He speaks more English than I do Amharic, but that’s really not saying much.

E-”Dinquinesh is bulls of first Ethiopian”
Me-”Bulls?”
E-”Balls of first Ethiopian.”
Me-”Balls of first Ethiopian?”
E-”Ishi” (yes)

Students of human evolution probably get the humor in this conversation. E was remarking about the fossil hominin–Lucy (who is known as “Dinquinesh” in Amarhic, roughly meaning “thou art wonderful”). Lucy was discovered by American paleoanthropologist Donald Johanson in Hadar, Ethiopia in 1974. She is a member of an ancient hominin species–Australopithecus afarensis–that lived approximately 3.1 million years ago.Of course, E was trying to tell me, “Dinquinesh is the bones of the first Ethiopian.” I’ll have to try to tell him about Ardipithecus ramidus and Ar. kadabba. It promises to be a very funny conversation in our pseudo-pidgin language.

In other news, fieldwork is going well. Beyond rewriting Ethiopian prehistory, I’ve experience the following highlights in the past month:

1. Ahab and Moby Dick returning to bachelor units after failed attempts to enter one-male units (see last year’s posts).
2. A battle between hamadryas baboons and geladas worthy of pay per view television.
3. Watching a ‘mechanic’ in a small Ethiopian village put our tire back on our field truck. He was wearing a grease-covered jumpsuit and smoking a cigarette as he worked. This qualifies him as a mechanic.

Until next time.

Back in the Simien Mountains

Hello all! This is my first post since arriving in the Simien Mountains National Park (SMNP), Ethiopia two weeks ago. Over the next two months, I will update BA&BHB with information gleaned from my pilot research on bachelor geladas living in all-male units here in SMNP. The past few weeks have been extremely busy–learning new bachelors, catching up with males from last summer who have since entered harems, adjusting to the altitude (~3200 meters above sea level), and trying out new recipes at our base camp for my colleagues’ pleasure (or displeasure).

Please check back in the coming weeks for updates from SMNP.