Why we yawn

Dogs do it, lions do it, even babies in the womb do it. Why do we yawn? Steve Jones, in this piece in The Telegraph, explores the idea of yawning as a sign of our humanity. 

However yawns arise, and whatever they signify, such a spontaneous copying response to a second person's signal of mood is an unmistakable sign of empathy; of an ability to understand and to react to someone else's state of mind. People with autism or with schizophrenia find it hard to do that – and they respond less to yawns than do most of us.
Empathy is what makes us into social and cooperative beings, and the speed and extent with which a person yawns in response to another's involuntary gape may be a quick and objective measure of to what degree he or she might be blessed with those useful talents.
Chimps do yawn, and they, like us, respond in kind when shown a computerised avatar indulging in the pastime. For them, though, the gesture is a statement of dominance rather than sympathy (with a strong hint of sexual aggression built in) and in other primates it may even be a sign of an imminent attack.
Perhaps what most people regard as an impolite act, to be disguised with a strategically placed hand when in company, is instead a deep insight into what it means to be human; a sign of an ancient shift from a quarrelsome and sexually violent mental universe to a generally cooperative and agreeable one. Man as a yawning rather than thinking ape – Homo oscitans rather than sapiens - may lack dignity, but reveals a new and attractive side to his personality.