One of our greatest misconceptions as a species is that solely human agency drove civilization. At least, that’s what Jonathan Kennedy argues in his 2023 book Pathogenesis: How Germs Made History. Throughout history, humans have often aggrandized themselves, overlooking the fact that the true hallmarks of survival and the shaping of civilizations are sometimes dictated by probabilistic outcomes, perhaps shaped by the planet’s unlikeliest organism: the humble germ. 

Kennedy challenges the notion that human agency is solely responsible for progress, instead highlighting how germs have become nature’s most formidable agents of destruction. By toppling empires, eradicating civilizations, and redrawing boundaries, germs have challenged human survival in ways that human agency alone could never achieve. In this way, germs have proven to be powerful architects of human history and society. 

What led to the eradication of Homo neanderthalensis and the rise of Homo sapiens? How did the Antonine Plague contribute to the downfall of the Roman Empire? Using a scientific and materialist understanding of history, Kennedy masterfully navigates the intricate web of anthropology, microbiology, and human history to highlight how microbes have redefined historical narratives and shaped the course of human narratives. It turns out microbes aren’t just invisible annoyances — they are potent architects of change.

The power of pestilence in human evolutionary history

Kennedy argues that human survival as we know it would not have been possible without human societies adapting to various pathogens.

In the early days of human history — over 300,000 years ago — Homo sapiens shared the Earth with several other human species, which Kennedy aptly compares to the different races of Middle-earth in the Lord of the Rings, but there wasn’t anything inherently remarkable about our existence as compared to, say, the neanderthals, that would favour us. 

Kennedy noted that an ancient species of human with stockier builds — who were either driven to extinction or assimilated by Homo sapiens — had greater cognitive capabilities earlier than we have credited them with, including skills like tool-making and artwork, which Homo sapiens wouldn’t exhibit for millennia. He argued that it wasn’t this misconception of Homo sapiens’ exceptionalism that led to our dominion over the planet but rather that microbes acted as tools of evolutionary change, drastically altering the survivability of different human populations. 

Modern-day Homo sapiens appeared nearly 300,000 years ago and would go on to craft elaborate cave paintings, wield fire, and bury their dead, much like us today. However, the majority of Homo sapiens’ history involves our ancestors sharing the terrain and interbreeding with other closely related species, such as Homo denisovans and Homo neanderthalensis — both extinct species of early humans that inhabited parts of modern-day Europe and Asia. By connecting the dots using fossilized and genetic evidence, scientists believe that as our ancestors traversed new landscapes and interbred with other subspecies, they built a robust toolkit of critical genes and more efficient cognitive abilities, ensuring their survival. 

Geological differences, animal domestication, and diverse water bodies exposed Homo sapiens to new pathogens, gradually strengthening their immune systems in ways that other species could not match. As competition for resources and skills intensified, other human species were gradually driven to extinction around 40,000 years ago. 

Pathogens and colonial exploitation

This evolutionary dynamic to determine survivability is not limited to specific epochs but has operated as a continuous and often brutal cycle of death and suffering, shaping the survival and success of human populations throughout history. Kennedy’s examination of the Spanish invasion of South America in the early sixteenth century under Hernán Cortés and Francisco Pizarro highlights the immunological advantage and the differing responses of populations to pathogens. While Spanish imperialists emphasized the superiority of their weaponry and tactics over the Aztec Empire, it seems implausible that a mere expeditionary force of 500 men could have possessed the ability to topple one of the largest and wealthiest empires on the planet at that time. 

The resulting Spanish invasion of Tenochtitlan in 1521 was not a matter of divine providence, as the Spanish believed, nor was it solely due to their technologically superior weaponry. Rather, it was circumstantial: the Spaniards were carriers of pathogens and diseases against which the Aztecs had no immunological defence, leading to the near eradication of the Aztec population. 

This immunological disadvantage benefited European colonial interests, contributing to the genocides of Native populations in the Americas who were unwittingly exposed to pathogens. As a result, Indigenous population numbers plummeted from 60.5 million to less than six million in just two centuries.

This massive loss of life not only altered the course of human history but also profoundly impacted the environment which led to a period of global cooling due to reduced human strain on natural resources.

Potential and pitfalls: Where Pathogenesis falls short

Kennedy encourages the reader to reevaluate humanity’s relationship with the natural world not as a hegemonic dominion, but as one of subservience, where survival depends on adaptability to adversity. His work highlights the profound role of causality in shaping history. 

While his approach is direct and provocative, Kennedy occasionally leans toward determinism — that all events are causally inevitable — which underestimates the role of human agency in shaping tangible outcomes. However, this narrative choice does not diminish his analysis; rather, it provides critical historical exposition and insights, inviting further academic exploration into the interplay between disease and history.

Nonetheless, Pathogenesis invites deeper reflection on how small things can lead to big changes. Especially in a post-COVID-19 world, it encourages us to respect the humble microbe and its profound influence on modern society. 

As antibiotic-resistant superbugs proliferate, reliance on animal agriculture increases, and environmental conditions worsen under the strain of a growing population, the threat of deadliner pandemics becomes increasingly likely. 

The question is not whether there will be another pandemic, but when. As a species, we have reached a fragile precipice that could quickly give way to a darker future. Kennedy’s book not only encourages discourse on reevaluating the role of microbes in our lives but also acknowledges our critical relationship with the natural world.