mise à jour du
3 août 2008
Praeger Ed
Westport. USA
An evolutionary psychology of sleep and dreams
Patrick McNamara


In primates, yawning may be contagious or a signal meant to synchronize sleep times. Yawning is associated with sleepiness and appears to occur in all mammals and in some birds, and may even occur in reptiles. Yawns are involuntary openings of the mouth, inspiration of a breath, closing of the eyes, and stretching of torso and limbs. Like REM sleep, yawning is associated with cholinergic excitation and dopaminergic inhibition. Oxytocin and testosterone infusions can induce yawns as well. Interestingly, when oxytocin is injected into paraventricular nucleus or the hippocampus, it induces both\yawning and penile erections. Yawning occurs in the fetus and throughout the life span.
In humans, at least one form of yawning is contagious-just the sight of another person yawning can trigger a yawn, suggesting a social function for yawning. When yawning functions as a signal (as in the case of contagious yawning), then t may acquire costly traits (placing the yawner in a vulnerable position, etc.). In that case, receivers will tend to use the signal to infer the current status of the -sender. According to costly signaling theory, the yawn would then convey a message that implies that the sender is currently handicapped ("I am not fully aroused and my attentional skills are flagging, etc., and therefore I am vulnerable"). But it is far from clear whether such an analysis helps us to understand the functions, if any, of contagious yawning. A far more likely explanation is that the contagious yawn serves to synchronize sleep behaviors of a group of primates.
Comparative data on other forms of (noncontagious) yawning in relation to sleep variables are lacking and thus not much can be said about their functions and potential relation to sleep. Nevertheless, the yawn's wide taxonomic distribution in the animal kingdom suggests an ancient lineage as well as an important functional relationship with sleep states. It would be interesting to know whether manipulations of yawning (i.e., inhibiting or enhancing rates of yawning) have systematic effects on either REM or NREM (or both). It would further be interesting to know whether yawning occurs in species with little or no REM.
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