Tragedy of the Blood Commons

(cross-posted at the Volokh Conspiracy)

Undead film and fiction are burgeoning with economic questions.  But the most glaring of these questions relate to the economics of food.  Vampires and zombies are both known for their peculiar and often voracious eating habits.  It’s natural to wonder whether there’s enough food to feed all those hungry mouths.

The movie Daybreakers explicitly addresses the question of how the undead can manage (or mismanage) the food supply, depicting a world in which vampires have hunted humans to the point of extinction — and consequently face starvation themselves.  When I first heard about the movie’s premise, I immediately thought, “Tragedy of the commons!”  Eventually, my reaction expanded into Chapter 15 of Economics of the Undead.  Here’s an excerpt:

To understand the perverse incentives that accompany open-access resources (also known as common-pool resources or “commons” for short), it’s useful to consider a short parable.

The vampire Reynaldo has trapped a young human woman in a dark alleyway. Just as Reynaldo is preparing to sink his fangs into her flesh and suck her dry, his keen hearing picks up something unusual… a second heartbeat. The woman is pregnant!

Reynaldo pauses for a moment, deciding what to do. Maybe he should let her go. If he does, then the woman will eventually give birth. At some later date, Reynaldo thinks to himself, he can trap her again, drain her, and still have her offspring left for dessert. And being immortal, Reynaldo isn’t so impatient that he couldn’t wait a while longer. Resisting his bloodlust for now seems like the rational thing to do.

And yet . . . if Reynaldo lets this woman escape, who’s to say it will be Reynaldo who gets to drink her later? There are plenty of other vampires out there, all of whom would happily take this woman’s lifeblood, and her child’s, too. If there are just nine other vampires out there, Reynaldo thinks to himself, then he has only a one in ten chance of being the lucky one. So it’s one meal for sure now, versus a 10 percent chance of two meals later. Reynaldo frowns as he does the math. . . .

And plunges his teeth deep into the young woman’s neck.

Repeat that same decision-making calculus for all the other vampires, and you have a recipe for overhunting of the human population — to the detriment of all vampires.  The basic problem is that the individual vampire reaps the whole benefit of feeding now, while the cost of that feeding (fewer humans left behind to breed) is shared among all the other vampires who prey on the same human population.

As the remainder of the chapter makes clear, humans have faced similar difficulties with managing common-pool resources.  The best-known modern example is the overfishing of the international oceans, which by one estimate has reduced the stock of large ocean fish to ten percent of its pre-industrial level.

To the uninitiated, overfishing might seems like a problem of excessive demand.  When people want a lot of something, they overuse it, right?  But that explanation is belied by the existence of other species, like chickens and cows, that are in no danger of extinction despite high demand.  As I put it in the chapter, “The key question is how vampires can make humans less like fish, and more like chickens and cows.”  And the answer lies in the institutions that govern economic life — in this case, whether renewable resources are treated as communal or private property.  Communal ownership tends to result in the overuse and destruction of resources, while private ownership encourages conservation.  The chapter, written from the perspective of a vampire economist, therefore makes the tongue-in-cheek proposal that vampires ought to privatize the humans in order to prevent a Daybreakers-like disaster.

Given the centrality of eating-and-drinking in undead lore, it shouldn’t be surprising to find the tragedy of the commons manifesting in other ways.  In Economics of the Undead, it comes up in at least two other chapters.

First, it arises in Tufte, Tufte, & Bishop’s chapter, “What Happens Next? Endgames of the Zombie Apocalypse.”  If the zombie horde eventually converted all the humans into zombies, the zombies would find themselves without neither food nor future hosts.  It is therefore in the zombies’ interest to restrict their consumption so as to foster a stable (or even growing) human population.  Like vampires, however, the zombies’ individual incentives may deviate from the optimal behavior for the group.  Unlike vampires, zombies lack the rational capacity to consider alternative institutional arrangements.  But as Tufte, Tufte, & Bishop argue, the virus that inhabits all zombies might evolve to solve the problem.  After all, a virus that leads to the extinction of its host species is not a well-adapted virus.  A superior zombie virus would moderate its hosts’ eating patterns.  This could be regarded as a quasi-centralized alternative to private property as a solution to the tragedy of the commons.  (Saturday Morning Breakfast Cereal offers an awesome comic version of this scenario.)

Second, the tragedy of the commons also comes up in Michael O’Hara’s chapter on “Zombies as an Invasive Species.”  O’Hara suggests that recreational zombie-hunting might provide a means of controlling the zombie population, much as recreational hog-hunting has helped to curb the feral hog population in some states.  But if zombies became an economically valuable species in this way, it’s possible that humans might overhunt the zombies, leaving too few zombies for future hunters.  As a solution, O’Hara says, we might see the emergence of private zombie-hunting preserves.

Returning to my own chapter, you might think that I’ve chosen an odd way to champion the concept of private property, given that most human readers would not fancy becoming part of some vampire’s herd — even if the herd were “free-range” and its members unaware of their owned status, as suggested in the essay.  Although I don’t address this concern in the chapter, I’ll address it here.

From a philosophical perspective, humans are unlike cows and chickens because they are intelligent and self-aware.  This distinction seems relevant to omnivores, less so to vegetarians and vegans.  But let’s set aside the philosophy for a moment.  Obviously, the best scenario for humans would be for vampires not to exist at all.  Next best would be “vegetarian” vamps who voluntarily refrain from eating humans (like Louis in the Vampire Chronicles, Angel on Buffy, and the Cullens in Twilight).  But if vampires really existed in large enough numbers to threaten the human population, if they resisted our best attempts to destroy them, and if they couldn’t be persuaded to go veggie, then wouldn’t we want vampires to at least find a way to conserve us?  Our survival as a species would depend on it.  Both humans and vampires would gain from the privatization.  Being oblivious, free-range humans might not be so bad.  Who knows?  Maybe we already are.