2. Let me suggest an idea about the adaptive function of sleep: It did not originally evolve for rest and repair (though those functions may have been layered on later, at least in some species). Instead, I’ll hypothesize that sleep was originally designed to keep an organism out of harm’s way during periods to which it is poorly adapted. Note that day and night can differ dramatically in lighting, temperature, humidity, abundance and type of predators and prey, etc., so an organism that was well adapted to one set of conditions would be relatively poorly adapted to the other. (This same hypothesis could explain hibernation, estivation, etc., not just day/night cycles.) According to this hypothesis, sleep helps organisms avoid temporal regions to which they are relatively poorly adapted.
A. Taking a reverse-engineering perspective, does this hypothesis make any predictions about the expected mechanisms involved in sleep? (To do this try answering what would trigger sleep and waking; where would organisms sleep; what would sleep look like?)
B. Considering my hypothesis about sleep, in what kinds of environments would you expect to see more sleep; less sleep?
C. Given your answer to B, how could you employ both convergence and divergence in formulating comparative tests of this hypothesis about sleep’s original function?