Perhaps this is not relevant, but I've long been intrigued by our family's sleep paterns in response to seasonal changes. Decreasing daylength and the long nites of winter always get longer sleep times, whereas the reverse holds true for the short nights of summer. Is it boredom, less work, or just a natural response? It must help to lower winter energy consumption, though that is not a deliberate response.

The evidence points to "natural response" as the reason why we northerners sleep more in winter and less in summer. People who live within the tropics do not display different sleep amounts at different times of year because day length varies so little in the tropics.

My body wants to hibernate during Minnesota winters, while during the summer I have manic energy and can get by on four or five hours of sleep.

Minnesota winters? Perhaps you have a scandinavian heritage? Back here in south Sweden, dawn is at around 0800-0900, and dusk at 1500-1600. I go to work in pitch black, sit indoors, get back home in total darkness. Literaly put on my peak oil hat, go feed the sheep in total darkness, bring in a days worth of firewood, clean away the droves of rodents left by the cats on the front porch, do some logging, go inside play with the children, make dinner, make love to my beautiful wife, do some logging, go to sleep. Thank god for my portable rechargeable LED lights, and without the physical activity I would be in hibernation 15 hours every day. And it's even worse further up north, but at least they have some snow to light up their existence. Global warming has killed the snow, so here comes winter and pitch black depressions.

Used to be in Vermont and other New England states the suicide rate went up during the winter. Then the snowmobile was invented. Now the death rate from snowmobile accidents is replacing the suicide rate :-}

Must be great in the summer though.:)