As one of Malthus’ four horsemen of human death, disease (& plague & epi/pandemic) has been a central force in human societies. Besides the obvious illness, death, and general misery diseases bring, despite being hidden in plain sight from humans until the 1880s, disease have been responsible for far more of human history and evolution than sociologists often realize. Consequently, sociology might benefit greatly from taking more seriously the role disease has historically played and the unique effects it has in modern, complex societies. 

Disease as Evolutionary Force
How has disease been a force producing selection pressures on human evolution? First, for a significant span of time, disease gradients, or ecological zones hospitable to humans that are surrounded by invisible ecological (disease) barriers, restricted geographic movement (McNeill 1996 [1976]). Like mountains or oceans (Carneiro 1970), disease reduced the space with which a given society could expand; at least without the appropriate technology for reducing the viability of the disease (e.g., clearing jungles). Less obviously, the lack of mobility also intensified pressures for political evolution, as population growth and density increased the odds of resource scarcity, internal conflict, and the need for centralizing risk (Johnson and Earle 2000; Abrutyn and Lawrence 2010). 

McNeill (1996) also underscores two forms of parasitism, macro and micro. Part analogy, part realism, he poses an interesting framework. Humans live by eating other organisms (macroparasitism), while parasites survive by using us as their host (microparasitism). The more “successful” a human society, the more disease becomes a prevalent risk. This is particularly true about 12-10000 years ago when sedentary human societies grew increasingly normal (Fagan 2004), accelerating exponentially with the evolution of urban societies in southern Iraq (Mesopotamia), Egypt, China, and the Indus Valley 5000 years ago (Adams 1966). “The result of establishing successful government is to create a vastly more formidable society vis-à-vis other human communities,” writes McNeill (1996;72-73):

[Hence,] a suitably diseased society, in which endemic forms of viral and bacterial infection continually provoke antibody formation by invading susceptible individuals unceasingly, is also vastly more formidable from an epidemiological point of view vis-à-vis simpler and healthier societies. Macroparasitism leading to the development of powerful military and political organization therefore has its counterpart in the biological defenses human populations create when exposed to microparasitism.

Success, then, meant greater precarity, which, ironically, set these societies up for greater success. What do I mean? With no value judgment in mind, societies that are bigger, have more advanced technology, and are better organized tend to conquer, colonize, and, sometimes, destroy their counterparts; while disease may ravage a population in the short-term, surviving an epidemic means immunity in the longer run. And, immunity usually adds an invisible devastating weapon that can lay waste to a neighbor, enemy, or innocent bystander in ways that make the bigger society even stronger and more likely to survive. Indeed, while we think of disease-wielding states as bad actors, McNeill reminds us that disease chains – or the circuits along which disease travels – are often built upon quite unintentional, normal human activities like foreign trade and tourism/travel; points quite salient in the summer of covid. Thus, like parasites that are unintentional organisms seeking to survive, sometimes human evolution proceeds accidentally and other times, like in modern biological warfare, purposefully.

The Hidden Consequences of Disease
At the nexus of evolution and political economy, there are other reasons to take seriously how diseases affect human societies. For instance, schistosomiasis, a water-borne disease that affects the exposed over their entire life course (Olivier and Nassar 1967), would have been a major problem beginning 5000 years ago at the dawn of the Urban Revolution (Adams 1966). Because it causes debilitating lethargy, the political elite’s survival in ancient Egypt, China, and Mesopotamia (Ruffe 1921) was always tenuous as an outbreak meant potential famine as peasants grew increasingly less efficient, dramatically reducing the surplus elites could expropriate.

A second example comes from a provocative – if controversial – theory posited by Rodney Stark (2006) suggesting disease is intimately connected to Christianity’s spread and, eventual, success in Rome and Europe. Using various sources of data, Stark argued that the two plagues that struck Rome (166 CE and then 249 CE) produced pressures that favored Christians who embraced the moral imperative to care for family, friends, and neighbors rather than see them as dangerous. The common solution to dealing with the sick was total quarantine, yet smallpox and measles (McNeill 1996) could be overcome with basic care like fresh water, rest, and monitoring. Christians, Stark argued, would have been more likely to care for their sick, and to extend this care to pagan neighbors. Surviving the plague, then, could motivate conversion either because of the affectual attachment to neighbors who helped and/or because of supranatural belief that the Christian God proved more efficacious and helpful than the pagan alternatives.

Sociology and Disease
What makes disease outbreaks sociologically interesting, then, is that they are an external exigency that molds human societies and social disasters – that is, ‘physical, cultural, and emotional event(s) incurring social loss, often possessing a dramatic quality that damages the fabric of social life” (Vaughan 1999:292). They are, however, a fascinating sub-category of disasters. On the one hand, diseases are connected to industrial/technological innovation, but not quite like nuclear meltdowns. Rather, the intensivity and extensivity of transportation and communication technology today, particularly the former, greatly amplifies the typical disease chain routes, as travel is easier, quicker, and more robust. The latter technological advance contributes by connecting humans in time and space, increasing the possibility of panic, collective trauma, and, conversely, potentially greater resistance campaigns to public health mandates.

On the other hand, disease are a natural disaster, sharing much in common with tornadoes and earthquakes, yet being qualitatively different. Specifically, it shares more in common with Malthus’ other horsemen of death (warfare, pestilence, and famine). For one thing, the effects are totalistic, in that they pose biological, psychological, and sociological risks . Threats of debilitation and potential lethality have obvious physical consequences, as well as metaphysical pain as actors question why and how a disease could indiscriminately affect loved ones and strangers alike. Disease also threatens social relationships, as all people – kin, kith, and strangers – are potential carriers of something invisible and harmful; something that can contaminate and pollute, as well as injure, maim, and kill.

Covid-19 has exposed just how vulnerable we are. To be sure, Trump has mismanaged and, perhaps, made significantly worse the consequences of the disease, but no country has escaped this unscathed, save for New Zealand. What is most disconcerting is that eight months into the pandemic, the specific reasons for why San Francisco and Vancouver have managed to reduce or constrain the negative outcomes while Los Angeles and Toronto have not remains murky. Indeed, mask-wearing reduces the spread, yet Canada has a lower rate of mask-wearing than the U.S.; and by most accounts, is handling the pandemic “better.”

Additionally, it has raised legitimate questions: how large and dense can a city, region, or nation can get before the dangers and risks outweigh the benefits? Is the model of neo-local, geographic mobility preferable to living near extended family and other close systems of support? Are pandemics going to be common? How do we mitigate the inequitable distribution of safety, security, and risk? How do we deal with segments of the population that see risk as individualized, thus putting strangers and friends alike in harms way? How does the federal government, in the U.S. respond to recalcitrant communities that see state intervention as anathema to local control?

These questions, and many others, remain unanswered and are worth digging deeply into; especially in the connected world we live in today. For instance, while marginalized groups are at higher risk of being exposed and dying from Covid-19, privileged groups do not have as many options for avoiding exposure as in the past. When Yellow Fever struck the American south in the late 1800s, the solution for those with means was to simply move further from the urban cores near the Mississippi River. Nearly 1/3 of Memphis’ population – mostly wealthy whites – simply picked up and left, leaving the poor and marginalized to deal with the disease (Rushing 2009). Disease chains, however, extend further and further into what was once isolated, safe space.

While Malthus’ predictions have been severely criticized, perhaps it is prudent to wait to see the final score. Or, more practically, to begin re-imagining a world in which diseases are real forces to contend with.