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.”
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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