I'm reminded that we still don't know conclusively what purpose sleep serves[1]. We know about things unimaginably distant in scale or time -- like quarks and the Big Bang -- but we don't know the answer to something seemingly pedestrian.
Oh, we do?
That's funny, Afaik quarks still confuse physicists because they behave erratically and appear to be composed of other particles. And the big bang is simply an assumption that makes the cosmological model work well for our human brains, but it is not how the universe started specifically.
We don't know jack shit, that's the bottom line, and we like to pretend we do.
http://www.goodreads.com/book/show/27068734-but-what-if-we-r...
I'd really like a source for the composite quark claim.
1. String theory has no experimental backing.
2. It doesn't posit that currently fundamental particles become composite.
For a decent explanation see:
https://physics.stackexchange.com/questions/38767/relation-b...
http://chem.tufts.edu/answersinscience/relativityofwrong.htm
Sure, maybe we know jack shit. But we know unfathomably more jack shit than in previous ages.
1. Ill-posedness of the problems: what is sleep?, why do animals sleep?, etc. vs. the well-posed physics problems such as, what happened at the beginning of the universe?
2. Data sufficiency: there is too much variability across people and animals to have enough representative data marginalized on each variable for many biological systems in general, and sleep in particular
3. Complexity of the system: cosmological systems and even subatomic particles are less complex models than biological systems
On incentives for researchers, there is also the maxim that there are many unsolved and interesting problems to work on, but scientific judgement is in knowing which are solvable. Of course, the occasional maverick goes after the hardest, most ill-posed, most unsolvable problem. But the existence of such mavericks is not guaranteed for every problem, sleep biology included.
"As far as I know, the only reason we need to sleep that is really, really solid is because we get sleepy."
I think in general, good-sounding theories produced by the "speculative evolutionary biology" game are actually very often right -- but only describe one facet of a supremely messy system with boundaries that don't conform cleanly to the mental models we try to impose.
We don't have similar separation between morning & evening, for example. (though I've always been a fan of the siesta)
[1] https://en.wikipedia.org/wiki/Non-24-hour_sleep-wake_disorde...