Instead of being a signal, yawning evolved as a social indication to notify others that we weren't as alert.
Professor Andrew C. Gallup of the State University of Fresh York Polytechnic Institute did a new study on this topic.
He arrived at this result by reviewing previously published scientific studies on the origins and implications of yawning in different animal species. They studied the psychological and social implications of yawning in both mammals and birds.
In the publication, Gallup, the study's lead author, says that yawns have a reputation for being spontaneous or contagious: they occur when no one expects them, and if one person yawns, the person watching yawns as well.
He emphasises that, according to this definition, every contagious yawn can be traced back to a single spontaneous yawn, implying that contagious yawning is a relatively new phenomenon.
According to Gallup, it began as a spontaneous event and is hence classified as physiological in nature.
He goes on to say that contagious yawning has only been observed in social species and that it only occurs after infancy. There have been various theories proposed to explain the physiological relevance of yawning, but none has been supported or refuted by convincing evidence.
Experiments on people, however, have demonstrated that inhaling increased or decreased levels of carbon dioxide or oxygen had no effect on the frequency of yawns.
As a result, it has long been assumed that yawning and breathing are controlled by separate systems, and that respiration has no effect on yawning.
He claims that the research suggests that yawning is more of a cue than a signal, based on the evidence.
"Yawning is a neurophysiological adaption that is prevalent among vertebrates," Gallup explains, "and the detection of this activity pattern in others appears to be biologically relevant among social creatures." It acts as a trigger, increasing individual vigilance and encouraging motor synchronisation through contagion."
He wants to know if spontaneous yawning originated expressly to communicate internal status or to affect the behaviour of viewers in certain species.