See ,Hear,Read or Think of Yawn,You Yawn.Why?

We yawn when we are sleepy and wake up.Why we yawn?Have you ever thought it is a sign of sleepy or wakefulness? Dmitry Arbuck，Meridian Health GroupIndianapolis，made a research for this interesting phenomenon.You can read the research paper for more details.

Infectivity and social contact

Contagious is the most prominent characteristics of yawn.Yawn is too easy to infection. Nearly everything related to it could inspire more yawning,including see ,hear,read or even think of yawn.Some people has found that silent film which shows yawn can infect nearly 55％ audience in 5 minutes,even those people who didn’t yawn ,has admitted that they at least being tempted.

There is some thing more interesting: If we remove the yawning mouth from the video,it can also arouse the audience to  yawn. Although a suddenly open mouth is the most significant part of the yawn. And, in turn, the yawn caused by yawning mouth alone is not as much as smiley face.Maybe it is because the open mouth is not only stand for yawning,but also singing or crying.It is the while face which makes us yawn,including the eyes narrowed.

Spontaneous yawning is very old  from the evolutionary point of view- most vertebrates have this behavior. While contagious yawning has a shorter history,it only appears in social mammals.Such as chimpanzee,maybe dog is included.

For human,we spontaneous yawn when we are still in the womb,but contagious yawning appears at the age of four or five.In this age,child can owe mental state  to itself or others.This further proves that the contagious yawning has something to do with social contact.

(source:SCIRP,guokr) 

Digression:When I completeed this artical,I have yawned heaps of times.