h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I came across this hypothesis, maybe it could become a full blown entry here on the h2g2 guide.

Contrary to contrary to popular belief yawning has nothing to do with lack of oxygen, it happens because we are tired. The latest theory, developed somewhere, supposedly proves this by subjects in a controlled environment of varying levels of oxygen yawning an equal number of times. Evolutionary Psychology no less.

Let us think back to our early ancestors, stone-age man and imagine him in a simple social group of between 8 and 12. Such a setup would have a basic hierarchy of group leader, younger and older males, mothers and children of varying degrees of dependency. As everyone sat around the fire each evening, bloated after devoring a whole wild boar and wondering about the meaning of life, people would quickly become tired. Someone yawns. As we all know, yawning is damn infectious (just like laughing). Very quickly and without realising it, everyone in the group is yawning. At this stage all the leader has to do is to announce that is time to go to sleep and he will have almost total consensus.

It seems that yawning is just a evolutionary ploy we have developed to aid tribe cohesiveness when going to sleep. We only do it when tired but the fact that it is unconsciously infectious is what makes it powerful.

How many times have you yawned while reading this entry?