The study of yawning is called chasmology. Apparently it’s an emerging field, and has developed some fundamental laws:
The ‘First Law of Chasmology’ states that a yawn occurs: (1) if the yawner cannot do what he would like to do, or (2) if the yawner must do something that he would rather not do. The ‘Second Law of Chasmology’, which is a special instance of the more general First Law, states that the yawn has an erotic and even a sexual aspect. A critical mass of proof for the validity of this Second Law is derived from various sciences and disciplines, ranging from theology and (the history of) art to ethology and pharmacology. The process of evidencing the Second Law has also established chasmology as an emerging science, i.e. a science that uses the data and information of primary sciences to make a synthesis that transforms and transcends the original scope and results of the auxiliary disciplines.
And here’s another brief summary on the state of chasmology:
In fact, the act of yawning can demonstrate a range of emotions including interest, stress and even wanting to have sex, The Telegraph reported……
Though an average person yawns 240,000 times during his lifetime, the actual theory behind yawning still remains a mystery. Scientists still don’t know exactly why a person yawns, although the common and most favourite theory is that it provides extra oxygen to the brain.