The act of yawning has been observed in all vertebrates, and occurs in humans as early as minutes after birth, so it must have some definitive physiological purpose. Until recently, most scientists believed yawning was a respiratory function, triggered by a surplus of carbon dioxide in the bloodstream. In the past decade, however, studies have suggested that yawning acts as a mediator of activity and arousal levels. The evaluation that follows will examine three such studies and the evidence they contribute to this hypothesis.

The first study (1) examined the connection between yawning and activity on a physical level. Previous research had drawn loose ties between arousal and yawning; for example, one study showed that yawning in rats increased with the presence of a penile erection. To show that arousal increases with the onset of a yawn, the authors of this study designed a correlational experiment to measure changes in physical indicators of arousal before, during, and after yawning. They predicted that signs of arousal would increase when the yawn started.

A mixed-gender group of 30 college students participated in three 15-minute l

As was the case with the previous study, the results of this experiment would be more accurate with the use of a larger and more diverse sample, particularly in the first experiment. Although the gender ratio was equal this time, all subjects were "professionals" who led very similar lifestyles. To get an accurate representation of the human population, people of different lifestyles and professions should be included in the sample.

The authors of the final study (3) tie together the two studies above and make new conclusions based upon the findings. By measuring both physical and psychological factors, the study sought to provide evidence for two theories: first, that yawning is associated with changes in activity levels, and second, that yawning is not affected by sleep depravation. One of the foundations for their assertion that yawning increases with frequent shifts in activity come from observations of different species of mammals. Sedentary animals, such as herbivores, rarely yawn; carnivores, on the other hand, constantly switch between periods of activity and inactivity and were found to yawn much more. The authors performed a two-part correlational study to determine the specific link between activity levels and yawning in humans. Like the authors of the previous study, they predicted that yawning would increase during low activity levels and decrease when subjects were more active. They also predicted that amount of sleep would not affect how much subjects yawned.

This data shows a simple relationship between yawning and activity level, and it can be concluded that yawning is a reliable predictor of an upcoming increase in activity level. Therefore, the authors suggest that yawns serve as a marker of a change in activity level, as well as being regulators of arousal. The study also disproves the common notion that sleep deprivation is a cause of yawning. The results clearly indicate that yawning frequency does not change when the amount of sleep changes.

Several conclusions can be drawn from these results that support and elaborate upon the authors' hypothesis. As predicted, tasks that are "boring" and have little social interaction make subjects more prone to yawning. Contrary to their nature, though, these tasks often require one to pay close attention. As the authors suggested, yawning may be a mechanism to induce arousal when attentiveness is necessary and the environment lacks stimulation. The fact that yawning frequency is highest in the hour after awaking and the hour before going to bed provides further support for this theory. For example, since subjects are naturally becoming sleepy in the hour before retiring (thus causing the arousal level to drop), the yawn may be the body's way of resisting fatigue by inducing arousal. Once the subjects went to bed no yawns were reported; they had, in effect, "given in" to being tired and no longer needed to induce arousal. Finally, since yawning frequency did not change with amount of sleep the previous night, the results of the study suggest that yawning is not related to sleep depravation.

Even though the study described above may have its imperfections, it is not completely useless in furthering our knowledge of why people yawn. It provides evidence from the physiological side of psychology to support a broad hypothesis that requires both biological and psychological evaluation. While the

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