Zombie Game Theory

I just watched the movie Warm Bodies, which is not so much a Zombie movie as a Romantic Comedy rehash of Romeo and Juliet in which half of the eponymous couple is of the undead persuasion. Which is probably why I enjoyed it so much (my second favorite: Shaun of the Dead). In any case, I think that the fact that the genre has enjoyed a great resurgence (AMC’s Walking Dead, the forthcoming World War Z) is a good oppertunity to talk about the game theory of zombies.

There is something very primal about the survival instinct aroused by the threat of a mindless horde of humanoids motivated only by a desire to kill you and take your most precious resource. The fact that these foes feel no compassion and cannot be bargained with, appeased, or deterred by show of force is almost written into the definition. In this case, there is no alternative than to fight or seek refuge. The compassion “switch” in our brain gets turned off, and we are prepared to kill in self-defense without hesitation. The fact that these beings resemble (or recently were) humans equipped with compassion or remorse is of no consequence, we are told to regard zombies as killing “machines” that will not stop for anything. This is an almost explicit version of tit-for-tat reasoning, in which thou shall not show compassion to those who cannot reciprocate is the only directive.

As Max Brooks, the author of the World War Z novels said:

The lack of rational thought has always scared me when it came to zombies, the idea that there is no middle ground, no room for negotiation. That has always terrified me. Of course that applies to terrorists, but it can also apply to a hurricane, or flu pandemic, or the potential earthquake that I grew up with living in L.A. Any kind of mindless extremism scares me…

Now we are entering the realm of game theory, as formulated by evolutionary psychology. It is adaptive to cooperate (and generally not harm) your friends, with whom you cooperate. However, should your friend have the misfortune of becoming a zombie, it is greatly maladaptive (to you) to show mercy. For your own survival, you must go into an antagonist mindset towards your (erstwhile) friend. This is the same antagonism you would generally feel towards strangers who encroached on your territory and are much more likely to kill you than come bearing goods with an opportunity to trade for mutual benefit. What is interesting is that this attitude can switch, at least towards the strangers, if they prove to be capable of cooperation after all. Then you might even learn to change your worldview to accommodate their change in status from mortal enemies to co-parties. In a world of shifting alliances, this must occur often, but importantly, never if the person is physically unable to show empathy, or at the very least, some enlightened self interest. Here mindless, as in “mindless zombie,” means an inability to have either.

But what if it is not apparent which classification to put a person into? Zombies resemble humans, after all. The movie Blade Runner confronted this issue head on. There is an inherent unease about not knowing if someone is a human capable of empathy, or a replicant, who is not. It is very wrong to murder fellow humans. It is obligatory to kill replicants. Making enemies into “other than human” is a very important goal of propaganda. This is also why zombies are “the dead,” since it is hard to achieve a greater state of “otherness” than entering the “other world.” Warm Bodies takes up this theme as well, but in a more Montague and Capulet sort of way.

There is, amazingly, an inverse of zombification. And that is love. As Steven Pinker points out, when searching for a mate, you would ideally want to find someone who won’t ditch you the moment it is to his/her advantage. He compares it to the signing of a long-term lease – you only want to commit if you can rely on something more than the rational choices of your potential mate, which could be swayed by other options, should they become available.

That is why many (all?) love songs proclaim the singer to be in the thrall of love and cannot escape, even if he (usually it is a he proclaiming his undying love) wanted to. Love is not just the ability to show compassion, it is inability to do otherwise.  If you think that “lover” is the additive inverse of “zombie,” Warm Bodies makes a lot more sense.

PS. Zombies are real. Some parasites affect the behavior of their hosts in ways that are very beneficial to the parasite (and detrimental to the host). Such as:

…the virus is harmful only to caterpillars of insect species, like gypsy moths. When a caterpillar bites a baculovirus-laden leaf, the parasite invades its cells and begins to replicate, sending the command “climb high.” The hosts end up high in trees, which has earned this infection the name treetop disease. The bodies of the caterpillars then dissolve, releasing a rain of viruses on unsuspecting hosts below.

Probably the most well-known example, are the zombie rats infected with Toxoplasma gondii, a protozoa that has part of its life-cycle in rats, and part in cats. The parasite, while in a rat, makes its host less afraid of cats, increases the probability that the protozoa will make it to its next phase.

Author: lnemzer

Associate Professor Nova Southeastern University

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