What's up with yawning

A quick search of the science blogosphere hit on the main hypotheses for why we yawn?  The cited blog posts below will lead you to the primary literature if you need it.

Common wisdom, and common sense, suggests that we yawn when we are tired because we are not getting enough oxygen and building up too much CO2.  However, like many elegant and simple hypotheses this one appears to be wrong.  The data suggest that gas content does not influence yawning.  We apparently do yawn more when bored, but this is not tied to slower breathing.

A relatively newer hypothesis suggests that we yawn to cool our brain when it gets to warm.  The idea is that the increased air flow will cool an overheated brain, as long as external temperatures are not too hot.  This idea has been tested in birds and seems to be supported by the data.

And yawning is contagious (I am yawning know - OK, a stale joke I found in all the yawning blog posts I read), at least in primates.  But interestingly, yawning is less common in humans with autism disorders, perhaps because they do not pick up on the social cue that others are yawning.  This social yawning response may be some sort of empathy behavior, and perhaps evolved due to some benefit of group yawning.  But it is unclear what that benefit would be.  Maybe if one member of the group has an overheated brain, everyone else probably does as well?

Yawning also seems linked to multiple human diseases - when you have these diseases you yawn more.  The mechanism behind this is unclear.

It is amazing that such a common behavior could remain such a mystery.

The search for an HIV vaccine . . . and a blood update

Check out this opinion article from Nature on the development of an HIV vaccine.  We will talk about it in lecture next Monday. (You will need to be on campus to have access to this article. Print it out if you need to read it from off campus.)

And this may be shameless self-promotion, but you might be interested in reading two recent blog posts of mine on blood stem cells (here and here).  Not required reading, but they are there if you are interested.