I read with great interest the proposal by Dave Cogan that Zombies reduce their rate of decay through sleep (Do Zombies Sleep, ZRS Blog 02/08/2011). This intriguing proposal relies on the reductions of energetic cost (metabolism) associated with sleep. Extending this suggestion, zombies may use sleep-like states of dormancy to prolong their existence, and may easily transition from slow semi-dormant states to more active predatory states. As such the two distinct “types” of zombie (slow poorly responsive Zombies common to early depictions and more modernly depicted “Rage Zombie”) may represent the same individual in its dormant and active state, respectively.
I would like to further extend this proposal, to predict that Zombies use a more profound form of dormancy, akin to mammalian hibernation. Hibernation is normally considered a phenomenon of small mammals, involving periods of low body temperature. Colleagues have recently shown the profound scope of metabolism in large mammals, black bears, during hibernation (Ø. Tøien et al., Science 331, 906; 2011). This research shows that such hibernation does not rely on greatly reduced body temperature as was previously supposed for hibernating animals. In addition, this work demonstrates that hibernation states can include periods of activity and responsiveness and that bears can continue to exhibit states of reduced metabolism (hypometabolic states) for weeks during normal activity following emergence from the winter resting period in the spring. Measurements from bears document remarkably low heart and breathing rates. Prior work has also suggested reduced organ function and blood flow during hibernation.
These findings suggest that hypometabolic states are the primary means by which most, if not all mammals, can reduce their energy expenditures for prolonged periods of time. My own work has suggested that the capacity for hibernation may be common to all mammals, and be a remnant of ways the body is regulated in newborns. This would mean that the genetic capacities to produce mammalian hibernation would be present in humans. As Zombies are based on humans, the capacities of humans are shared by Zombies. The Zombie state may then be, in part, an expression of this hibernation state. Furthermore, during hibernation, the primary source of energy is not the intake of food, but metabolism of stored fat. Fat is such an important resource, that animals build up body fat stores in anticipation of hibernation.
Most humans have relatively low fat reserves (even morbidly obese humans rarely achieve the 50% of body weight made up of fat typical of hibernating animals), so stored fat reserves are not available to the typical Zombie. If fat metabolism is essential for hibernation, the hibernating Zombie would require an additional source of critical fat. In mammals, the tissues with the highest concentrations of fat are brain and liver. A drive to fuel metabolism with fat may underlie the Zombie compulsion to preferentially feed on brain. The remarkably low heart and breathing rates, organ function and blood flow of hibernating animals closely resemblel those predicted in Zombies, and explains not only the difficulty in injuring Zombies by damaging the torso (assaults on the heart, lungs, organs and blood supply are seemingly ineffective) but also the remarkable abilities of Zombies to exist underground or under water with limited access to air.
I propose that Zombies can inhabit a state of dormancy similar to mammalian hibernation, and that this state can explain the coincidence of both slow moving and rage Zombies. Furthermore, this Zombie hibernation state explains the difficulties in killing Zombies, as well as their compulsions for eating brains. Come the apocalypse, I will be eager to confirm my thesis.
Dr. Michael B. Harris
Associate Professor of Neuroscience and Integrative Physiology
Institute of Arctic Biology, University of Alaska Fairbanks
ZRS Scientific Advisory Board member