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


  1. I like this! It also suports my idea that a zombie could not be truly dead. There are to many bodily functions involved with a feeding zombie in order for it to be DEAD. The whole rotting thing could be explained by extremely poor blood flow.

  2. Very interesting. But animals that hibernate have a different kind of fat than you, me and maybe zombies: it’s called brown fat. Regular old human body fat is called ‘white fat’. When it’s burned it goes through several steps that provide the necessary fuel for shivering. Shivering is one way our bodies produce heat, the constant action of the muscles raises the core body temperature. Brown fat is different. The metabolism of brown fat skips the shivering step and can be oxidized directly by the mitochondria of the cell thereby directly producing heat. Something called ‘non-shivering thermogenesis’. Maybe zombies have alterations in their body fat composition! I will have to do a fat biopsy on my next zombie autopsy!

    Maybe the zombie is in a constant state of hibernation, they don’t defecate, urinate, or drink, and can go long periods without eating. Some bears can go up to 7 months without eating, drinking peeing or taking a crap. How is this possible? The fat animals burn while hibernating gets converted into water, carbon dioxide and urea. Urea is one of the components of urine and is how the body rids itself of nitrogen waste. The urea in the hibernating animal enters a process called the urea cycle and gets turned into amino acids. The amino acids then get shunted into various protein synthesis pathways and where they get converted into protein. Because of this, the hibernating animal does not lose any lean body mass while sleeping the winter away. Just like zombies, they don’t seem to lose weight!

    Another interesting aspect of hibernation is that many animals slow their heart rates down to a fraction of what it is in the warmer months. The chipmunk has a resting heart rate of about 200 beats per minute, but when it hibernates, the heart rate can slow to 5 beats per minutes. Some animals and reptiles stop breathing all together! If the zombie was in a state of hibernation, it wouldn’t need to breath or have a heart beat, maybe that’s why they don’t die when you shoot them in the chest!

    Finally, bears have high levels of testosterone while they hibernate, which may explain why they get so pissed off when you wake them up; but more importantly in regards to the zombie, maybe the extreme acts of aggression are really just ‘roid rage!

    Just some thoughts!

    Peter Cummings, MD
    Forensic Pathologist/Neuropathologist
    Newbie ZRS Member

  3. I think this is a very interesting article and covers a lot of good points. If you watched the AMC show “Walking Dead” after the sheriff left the house in the city there was a zombie resting on the curb until he came out which unknowingly supports this theory. Although I don’t believe Zombies are brain eating creatures. I don’t think they pass up an exposed brain but the brain would be hard to get at and if zombies regularly ate brains they would render their own species extinct. That is of course assuming that to kill a zombie a shot to the head is what would finish them off.
    Another thing that this article brought to my attention is the fact that Bears would be an especially dangers creature to the Zombie. Bears like to kill it’s prey then leave it to decay before devouring it. The Zombie population would be wise to stay clear of the woods.

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