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mise à jour du 7 mars 2002
 télécharger l'intégralité de cette thèse au format pdf
 Yawning: an evolutionary perspective
The evolution of yawning :
why do we yawn and why is it contagious ?
Eric Schniter
thèse présentée devant le Department of Anthropology and the Graduate School of the University of Oregon in partial fulfillment of the requirements for the degree of Master of Science August 2001

Chat-logomini

Cette thèse originale, plus anthropologique que neuropsychologique, se propose de replacer le bâillement dans le scénario de l'évolution, tant du point de vue de sa physiologie, que dans sa fonction de communication. Après un parcours taxinomique fouillé, E Schniter explore les liens qui peuvent se tisser entre fréquence et type de bâillements en fonction de l'âge, des hormones et d'agents pharmacologiques, de l'environnement, etc, au sein de multiples espèces de primates. Il passe en revue les études sur le bâillement chez l'homme et semble attacher une grande importance aux théories de Nolman (parues dans Paradigm avril 1998) sur l'impact du bâillement dans la circulation du liquide céphalo-rachidien, mais non disponibles dans les revues médicales.

Son apport personnel est une tentative d'exploration de la contagiosité du bâillement, en affinant les méthodes antérieurement utilisées par R.Provine (dont la critique parait bien sévère et déplacée): dosage de la testostérone salivaire des sujets étudiés, stimulus par des acteurs en situation de comportement de supériorité, ou de soumission, comparaison avec une mire colorée, enregistrement vidéos des sujets au lieu de leur propre témoignage...Tout ceci afin d'avoir une comparaison possible avec l'étude des comportements de bâillements des primates. L'importance de l'échantillon de sujets étudiés, 110 étudiants de son université, parait ambitieuse. Hélas, la multiplicité des variables prises en compte réduit la pertinence des conclusions qui me sont apparues bien confuses. Vu la rareté des études sur le bâillement, il faut néanmoins saluer l'effort méritoire fourni pour mener à bien un tel travail.

Résumé : Though common across the animal kingdom, little is known about why we yawn, and even less about why yawning is contagious in humans. By means of literature review and laboratory based study, this thesis investigates why we yawn and under what circumstances observation of yawns elicits a contagious response. Previous studies have failed to investigate effects of dominance, sex, and hormones on yawning contagion.

Research suggests that yawning helps facilitate transitions between activities. Costly signaling theory suggests that because yawns signal anticipated change in activity, they impose a certain "cost" by revealing critical information about the yawner; therefore, dominance factors, sex, and hormones should all affect the frequency of contagious yawns.

The experiment sampled subjects' salivary testosterone and recorded their reactions to short videos featuring various yawn stimuli, in an effort to understand better the evolution of an apparently widespread feature of social signaling, controlled subconsciously by social and physiological criteria.

Table of contents (télécharger ce résumé et le sommaire de la thèse)
I. Introduction
 
Why Study Yawning? .1
All People Yawn, but No One Knows Why .1
Yawning is Not What It Seems .3
Yawning as a Social Signal .4
 
How to Study Yawning .6
Using Multi-disciplinary Ethology and the Evolutionary Paradigm .6
Searching for a Homologue of the Human Yawn .8
Analysis of Yawn ëDesigní in Humans and Between Species . 9
The Evolutionary History of Yawning . 10
 
II. Review of literature
 
The Existence of Yawning Across the Animal Kingdom . 13
Yawning in Birds. 13
Yawning in Fish. 16
Yawning in Reptiles . 18
Yawning in Non-primate Mammals . 19
Yawning in Primates . 22
Which Species of Primates Yawn?. 22
What Types of Yawns Exists, and With What Relative Frequencies Do They Occur?. 24
Yawning Frequency Correlated With Age, Hormones, and Drugs. 29
Yawning Frequency Correlated With Dominance. 31
Yawning Frequency Correlated With Sex. 33
Yawning Frequency Correlated With Environment and Stress . 37
The Relationship of Yawns to Canine Displays and Threat Gestures. 42
Yawning Contagion and the Communicative Value of a Yawn. 45
Discussion of Non-Human Literature on Yawning. 46
Observations and Studies of Human Yawning. 48
Physiological Studies. 48
Behavioral Studies. 54
Discussion of Human Literature. 57
 
III. Predictions
 
Pharmacological and Physiological Influence. 61
Psychological and Social Influence. 64
 
IV. Why is yawning contagious ?
 
Study Description. 73
Introduction. 73
Stimulus Development. 74
Dominant Yawn Stimulus. 75
Submissive Yawn Stimulus. 76
Null Yawn Stimulus. 77
Description of Subject Population . 77
Methodology . 78
Activities Involving Subjects. 78
Method of Data Collection. 79
Saliva Sample. 79
Video Taping and Observation . 80
Questionnaire . 81
Data Disposition. 81
 
V. Results
 
Introduction. 83
Study Effects. 84
Effects of Stimulus vs. Control Condition. 84
Differences in Yawns Elicited Across Experimental Conditions. 85
Verification of Video Dominance Manipulation. 86
Effects of Dominance Perceptions. 91
Subject Self-Reports of Dominance. 91
Reports of Self-Dominance and Actor-Dominance. 91
Female vs. Male rating of Dominance. 97
Effects of Relative Dominance on Contagious Yawning. 99
Effects of Sex Differences. 103
Sex Differences in Yawning. 103
Differences by Video and Sex in Yawning. 105
Sex Differences by Target Differences in Yawning. 107
Self Reported Statistics of Yawning. 110
Self Reports of Yawns. 110
Differences by Video and Sex for Feels Like Yawning. 111
Control vs. Yawn Condition for Feels Like Yawning. 111
Female vs. Male for Feels Like Yawning. 111
Sex Differences by Target Differences for Feels Like Yawning. 112
Latency and Yawn Contagion. 113
Yawn Related Activities. 114
Confounding Factors. 116
 
VI. Summary of findings and conclusions
 
Findings and Conclusions. 119
Discussion. 122
Considerations for Future Studies. 122
Final Discussion. 123
 
Appendix
a. questionnaire #1: for subjects who watched a video with an actor in it
b. questionnaire #2: for subjects who watched a video with no actor in it
c. recruitment flyer. 126
d. consent forms. 128
e. consent forms. 131
 
Bibliography. 142
 
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-Walusinski O Prostaglandines, adénosine, sommeil & bâillements 2004
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