Making contagion social: Epidemiology, calculus and the theory of happenings

The beginnings of formal epidemiology are conventionally marked by the introduction of mathematical modelling in the early 20th century. However, Ronald Ross, colonial medical officer and 1902 Nobel laureate for his proof of the insect vector of malaria, envisioned the future of mathematical epidemiology as a much more expansive project, one that would eventually exceed the remit of a medical science. This article introduces and analyses Ross’ theory of happenings as an attempt to generalise the concept of contagion as a non-material form of social organisation. To contextualise this approach, I explore the parallels and the common references between the mathematical method of epidemiologist Ronald Ross, and the work of sociologist Gabriel Tarde, who wrote Laws of Imitation (1890), to establish a relative and universal sociology. Both conceptualisations of contagion disregard a meaningful boundary between the natural and social world, they focus on affect and affectedness to embrace a radical plasticity in the human subject, both champion a philosophy of the infinitesimal to reject simplistic causes for social processes and to analyse large occurrences by focus on the vanishingly small. These parallels provide an opportunity to challenge assertions of a schism between the social sciences and the project of formal epidemiology, and to instead consider the contours of a different kind of social theory at the heart of the modern epidemiological project.