Courtesy of Hannah Carey
 OUT COLD: The Spermophilus tridecemlineatus or thirteen-lined ground squirrel, assumes a spherical posture when in torpor to reduce its surface to volume ratio and therefore rate of heat loss. Its heart rate will go as low as 3-5 beats per minute and its body temperature to just a degree or so above ambient temperature. In this cold room, that's 3° to 4° C.

As days shorten and the cold encroaches, roughly two dozen mammalian species fatten up and settle down for a long winter's nap. Humans, however, continue to trudge through the frigid darkness, and researchers aren't entirely sure why. Total human hibernation is a bit far-fetched, yet many mammals--from bears to shrews--hibernate, and researchers want to know more. "The general feeling is that hibernators have the same collection of genes and proteins that humans do, but express them at different places and times," says Hannah...

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