American Scientist

To the Editors:

Robert Provine's article "Yawning" (November-December 2005) nicely reviewed his work on this interesting topic. I disagree, however, that contagious yawning is restricted to humans and chimpanzees and that it thus reflects the high-level cognitive processes and social complexity of humans and our closest relatives.

In their 1967 paper in The Auk (84: 571-587), Edgar G. F. Sauer and Eleonore M. Sauer presented (admittedly non-experimental) evidence suggesting that yawning is also contagious among ostriches. In addition, other behaviors such as preening, grooming, dustbathing and feeding are often contagious in many species of birds and mammals.

Some confusion may result from the fact that most authors use the term "social facilitation" rather than "contagious behavior." While these terms are synonymous, many have incorrectly defined social facilitation too broadly to also include behavior that increases in the mere presence of other members of the same species.

Brian Palestis
Wagner College
Staten Island, NY

Dr. Provine responds:

Sauer and Sauer observed that "a bird that yawns quite often makes one or several neighboring birds yawn too, and yawning … can spread out like a 'snowball effect.'" However, unlike the fact of yawning, proof of human-like contagion in a group requires experimental verification that observed yawns are the vector for the synchronized response, not a commonly experienced physiological state (e.g., waking, drowsiness) or stimulus. This higher standard for evidence has been met only in humans and common chimpanzees, although contagion need not be exclusive to primates. Until the necessary research is conducted, the less restrictive term "social facilitation" better describes ostrich yawning and other socially synchronized acts (say, grooming or feeding). A startled herd does not experience contagious running. Where it is found, contagious behavior is hardly the pinnacle of social engagement. Yawning and other contagious behavior are better evidence for a low-level neurological substrate for sociality than a "high-level cognitive process."