Scientific American‘s Michael Shermer gets at the root of why we’re so fascinated with the walking dead:
Zombies, for one thing, fit into the horror genre in which monstrous creatures—like dangerous predators in our ancestral environment—trigger physiological fight-or-flight reactions such as an increase in heart rate and blood pressure and the release of such stress hormones as cortisol and adrenaline that help us prepare for danger. New environments may contain an element of risk, but we must explore them to find new sources of food and mates. So danger contains an element of both fear and excitement.
We also have a fascination with liminal beings that fall in between categories, writes philosopher Stephen T. Asma in his 2009 book On Monsters (Oxford University Press). The fictional Frankenstein monster, like most zombies, is a being in between animate and inanimate, human and nonhuman. Hermaphrodites fall between male and female, and hybrid animals fall between species. Our innate templates for categorizing objects and beings are modified through experience, and when we encounter something or someone new, we check for category matches. Moderate deviation from the known category generates attention (friend or foe?), Asma says, but a “cognitive mismatch” elicits both dread and fascination.
Distinguishing between zombies and nonzombies also hints at the deeper problem of xenophobia, which evolved as part of our nature to be suspicious of outsiders who, in our evolutionary past, were potentially dangerous. People from other groups, especially those perceived to be a threat, are moved into other cognitive categories and relabeled as mongrels, pests, vermin, rats, lice, maggots, cockroaches and parasites—all the easier to destroy them.