I remember finding a few interesting articles last year on medline
about sleeping. Unfortunetly, I don't remember the author or journals,
but the jist of his argument (with some evidence) was that sleeping
developed at least partially to let our brains cool down at night. He
hypothesized that our sleeping is kind of like a lizard (cold-blooded)
awake. He went on from there. It was a bit out there, but quite
interesting, and sounded a little plausible.
Look on medline for sleep, birds or chickens or something, reptiles,
and other similar combinations.
Dept of Zoology, Univ of Washington
meir at zoology.washington.edu