[The phylogeny, ethology and nosology of yawning]

Charles Darwin would have said that yawning was a useless piece of physiology. If so, then how should the survival of this very stereotyped behavior among the poikilothermal and homoeothermic vertebrates, from the basic brained reptiles to human primates, whether in the air, on the land or in the sea be understand? This issue of the ethnological, neurophysiologic and neuropsychological literature depicts yawning as being associated with an alternation of "awake-sleep" rhythms, sexuality, and nutrition, where it appears as a reference behavior of the mechanisms stimulating the state of vigilance. In pharmacology, yawning is used as an indicator of dopamine-ocytocinergic pathway activity, but in the Parkinson patient the neurologist sees it as an expression of therapeutic dopaminergic activity. J.M. Charcot and his school considered yawning as a clinical sign, long since forgotten. However, many patients complain about excessive yawning. Iatrogenic causes are the most frequent and can be found among many neurological diseases: vasovagal syncope, migraine, epilepsy, hypophyseal tumor, or stroke. Our ability to achieve motor and emotional behavior in resonance with others is deeply rooted in hominid evolution, and probably explains the strange phenomenon of contagious yawning.