====== Yawning ======

The physical and psychological sequences which occur during the yawning process have been widely studied. Nevertheless, the// reasons// for yawning are disputed and unclear - as is identifying an evolutionary reason to explain the need for it.

>  "There are a number of theories that attempt to explain why animals yawn. It is likely that there are a number of triggers for the behavior. However, there are a few select theories that attempt to explain the //primary// evolutionary reason for the yawn. None of them has been empirically substantiated."
>
>Source :  [[http://en.wikipedia.org/wiki/Yawn|Wikipedia]]

Yawns are common not only in most (if not all) species of mammals, but also occur in reptiles and fish - suggesting a very deep-rooted and ancient,, but as yet unknown, origin.

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Also see: [[content:life_sciences:human_body:contagious_yawning|Contagious Yawning]] and [[content:life_sciences:human_body:stretching|]]