Mathematician Thomas Woolley and coauthors claim that mathematical modeling can help us understand the movement of zombies, and thus how best to avoid encounters with them. Naturally, we here at Economics of the Undead applaud the application of theoretical models to zombies. But Woolley’s model provides an excellent example of why theory has to be tested against data – in this case, the observed behavior of zombies in film and fiction.
According to Woolley et al., zombie movement can be described as a “random walk,” a notion that has been employed in theoretical models in both physics and economics. Basically, the idea is that each step of a zombie is a random draw: he could move one step in any direction, and then another step in any direction from there, and so on. Over time, Woolley and his coauthors argue, this should lead to diffusion of zombies over the available domain.
But this is inconsistent with how zombies actually behave, if existing zombie narratives can be taken as any guide. Rather the diffusing over the landscape, zombies tend to appear in clusters and mobs, even long after the initial invasion. In a conflict between observation and theory, it pays to look for a better theory. And fortunately, there is one available. In Chapter 7 of Economics of the Undead, “Order, Coordination, and Collective Action among the Undead,” Jean-Baptiste Fleury and Alain Marciano suggest that zombies do not simply wander about randomly attacking people, but in fact display a range of behaviors that allow them to coordinate their behavior for mutual advantage (with other zombies, not with humans). Among other things, zombies tend to flock together for strength in numbers — the best-known example being the famous “zombie ant-pile” seen in the movie World War Z.
“Actually, the very fact that zombies gather in large and stable flocks, as most accounts will confirm, is evidence of an ordered society,” Fleury and Marciano argue. “If zombies were not ordered, they would wander chaotically and scatter into the wilderness, like particles of smoke into the air.” That description sounds a lot like Woolley’s prediction. “But such chaotic behavior would seriously undermine zombies’ ability to hunt and eat human flesh,” they add, supporting their claim with evidence from various zombie narratives:
Due to limited agility and cognitive abilities, a zombie is not much of a threat when hunting alone. Many action sequences in The Walking Dead TV series illustrate this point: Rick and his friends are generally pretty effective when it comes to fighting with roaming individuals as well as small groups of zombies. But when attacked by hordes of “walkers,” as in the last episode of the second season, Rick and his friends are quickly overwhelmed and eventually escape only at great cost. As confirmed in many accounts, such as Romero’s Night of the Living Dead, flocks of zombies are most dangerous to humans: they can exert tremendous collective pressure so as to break down manmade barriers and barricades. Thus, zombies tend to gather in stable groups, which help them maximize their chance of success in case of confrontation with humans.
But what could be the source of such cooperative tendencies? Fleury and Marciano suggest three possibilities. First, zombies may retain some basic tendencies written into their human DNA, including the basic desire to congregate with others of their kind. Second, they may retain some rudimentary memories of their prior human existence and cultural background. (In Romero’s Dawn of the Dead, one character famously explains the convergence of zombies on a shopping mall as resulting from “a kind of instinct, a memory [of] what they used to do” because “this was an important place in their lives.”) Third, the zombie virus itself may endow its hosts with any number of tendencies beyond the obvious craving for human flesh. It is well-known that parasites can affect the behavior of hosts – the most famous example being toxoplasma gondii – so it shouldn’t be surprising to find the zombie virus does so as well.
Whatever the cause, Fleury and Marciano’s claim is borne out in countless zombie narratives. Despite their shambling gait, zombies do not appear to follow a random walk. By all indications, zombies are guided instead by a tendency to flock with other zombies in a manner that increases their efficacy in confronting their much-smarter human prey.