The 2014 premier of The Walking Dead —AMC's postapocalyptic dystopian television series about zombies—was the most watched cable show in history. There have been a slew of popular zombie films such as Dawn of the Dead, Day of the Dead, Night of the Living Dead, 28 Days Later, I Am Legend and of course the perennial favorite Frankenstein. There is even a neuroscience text on the zombie brain, Do Zombies Dream of Undead Sheep? by Timothy Verstynen and Bradley Voytek (Princeton University Press, 2014), in which the authors consider real disorders that could turn the living into the living dead. Why are we so intrigued by zombies?

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. Add the emotion of disgust triggered by slime, drool, snot, blood, feces and rotting flesh, and we may find ourselves both repelled and drawn to such liminal creatures.

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. Such labels are inevitably applied to new out-groups moving into the territory of an established in-group or conflicting economically or culturally with one—blacks moving into white neighborhoods, Jews establishing businesses in gentile-dominated markets, the Hutus resenting the dominant Tutsis in Rwanda. Fundamentalist Muslims do not “hate our freedoms” (as President George W. Bush conjectured). Instead, as Asma notes, they created a uniquely American monster in which “we are seen as godless, consumerist zombies,soulless hedonists without honor, family, or purpose.”

On our cognitive maps are areas labeled “Here Be Monsters,” where we put outsiders perceived to be dangerous. Fortunately, we have learned to curb such chauvinisms. As a result, the moral sphere has expanded to include all racial and ethnic groups as worthy of respect and equality, in principle if not always in practice. We have done so, in part, by overriding our instinctive impulses through reason, allowing us to take the perspective of another. Shakespeare worked out the logic in The Merchant of Venice when he has Shylock ask:

Hath not a Jew eyes? Hath not a Jew hands, organs, dimensions, senses, affections, passions; fed with the same food, hurt with the same weapons, subject to the same diseases, heal'd by the same means, warm'd and cool'd by the same winter and summer, as a Christian is? If you prick us, do we not bleed? If you tickle us, do we not laugh? If you poison us, do we not die? And if you wrong us, do we not revenge? If we are like you in the rest, we will resemble you in that.

Perhaps zombies and other fictional beings stimulate those neural regions of our nonzombie brains that allow for a healthy and nonviolent outlet for such ancient callings.