How Germs Shaped History

“History is written by the victors,” goes the oft-misattributed (to Winston Churchill) quote. It may be true if you only look at human conflicts – battles, wars, and the like. But one thing that is abundantly clear from reading Pathogenesis is that germs have been making losers out of us since the very beginning. Worst of all, we didn’t even know it.

Much like how much of human existence was spent walking around in total ignorance of the world visible down the lens of a microscope, our many losses against infectious disease have also gone completely unnoticed; pivotal moments in our historical memory may not just be the result of feuds between people, but rather shaped and decided by the activity of germs for thousands of years.

This very argument is laid out by Jonathan Kennedy in Pathogenesis, subtitled Eight plagues that made the world in the US and How germs made history in the UK. It’s a bold, striking hypothesis: Everything from the migration of hunter gatherers to the emergence of capitalism is fueled by our microscopic adversaries. I spoke with Kennedy at length about his approach to the book – and the science behind it.

The following interview has been edited for readability. Watch the full, unabridged interview video above.

Could you please introduce yourself?
 

My name is Jonathan Kennedy. I’m a reader in global health and politics at the Faculty of Medicine and Dentistry at Queen Mary University of London. I’ve just written a book called Pathogenesis that tries to transform the way that we think about history.

When we think of the natural world, we think of it as a stage. But the more that we learned about the world that we live in, we realized that we’re not living on a stage. We are very much part of the system. It’s a pretty precarious ecosystem in which we play a rather minor role, and in which pathogens and microbes play a really crucial one – both in the way that the planet functions, but also in the way that our own bodies, and even our own minds function.

The starting point for the book is this question: If microbes have such an enormous impact on us as individuals, what impact do they have on the body social, the body economic, and the body politic? What impact do they have on aggregations of bodies, on society, on the whole of human history? I start off by looking at the extinction of Neanderthals 50,000 years ago and wizz through history in about 300 pages – eventually looking at COVID-19 and the future.

What sparked your research into this topic?
 

I had quite a revelatory moment where I began to realize the importance of research done over the last 20 years – the increasing amount of evidence that showed that gut bacteria are capable of influencing our brain function. It really blew my mind, if you’ll excuse the pun.

The broader context of this was COVID-19 – an event that quite quickly took on cliche to describe it: Unprecedented. As someone who has an interest in history, I knew that wasn’t the case! I knew that infectious diseases have played a massive role in history and they've killed millions and millions of people at a time. But they’ve also created the space for new ideas and for new societies to emerge. And that got me thinking how this is one of the major driving forces of history. We often think about great men and women being the driving force of history or, if we’re on the left, we may think about class struggle. But it was really interesting when I started looking at the topic of history through the lens of the pathogen. You start to see things differently.

What research surprised you while you were writing your book?
 

One of the really striking things for me as a layperson was reading about retroviruses and the way in which retroviruses could insert their DNA into ours, and if they infect a sperm or an egg, this gets passed down from generation to generation. Scientists talk about something like 8 percent of DNA in the human genome coming from these retrovirus infections. This knowledge was mind-blowing enough, but then to learn that there are studies that show this isn’t only junk DNA that humans seem to have acquired. Things like the ability for the placenta to bind to the uterus or the ability to form memories. The way in which information seems to pass from brain cell to brain cell seems to have been acquired from retrovirus infections.

We are taught the Darwinian idea of evolution through natural selection. This is an important aspect of evolution, but it wasn’t just through conflict between and within species that evolution occurred. It was also through collaboration between our distant ancestors hundreds of millions of years ago and viruses.

Why should we be studying and recontextualizing the history of disease?
 

For one, it’s fascinating. It's a really interesting story that overturns the way that a lot of us think about the world. And it contains some really important lessons. Even if we go back as far as the first written histories, Athens went to war with Sparta and thought it would win. But the plague of Athens struck. Nothing did them more harm, it killed about a third of the population, including the army. It killed Pericles, the great general and statesman. Eventually Athens lost and Sparta won. I think there’s a lesson there for our own times in a way that we shouldn’t be too hubristic. In many ways, the success of our own society has created the kind of conditions that might bring about its downfall, whether that’s AI, climate change, or infectious diseases. Certainly, it seems like we’re living in a new golden age for infectious diseases. Think of the unprecedented population growth, the encroachment on animal habitats, the industrial scale of factory farming, the kind of ease in which we can travel across the world. These have all combined to create almost perfect conditions for pathogens to hop the species barrier and spread quickly throughout the population.

How aware were people in the past of having immunity advantages?
 

That’s a really good question. Certainly it must have been bizarre for the conquistadors. We often underestimate how advanced and how strong some of the civilizations were in the Americas before the European conquest. The capital city of Tenochtitlan, which is on the current site of Mexico City, had a population of something like a quarter of a million people – four times as big as the biggest city in Spain.

Pandemic after pandemic literally decimated the population of the Americas; you see the population falling from 60 million to 6 million within a century. In the days before germ theory, the best ways to explain this would be God or racism, or both. Terrible explanations in my opinion, but we can again understand a lot about the contemporary world by realizing how long lasting the legacy of those explanations have been.

One review said the book was more “marxism than microbiology.” How do you respond to that?
 

The book certainly looks at history from the perspective of pathogens and infectious diseases, but it would be too simplistic to say that pathogens explain all of history. Often they come in on the side of one group or another and play a crucial role. I think that review in Nature was particularly pointing towards the explanation of the transition from feudalism to  capitalism.

My explanation of history draws really strongly on the work of Robert Brenner, a professor of history and sociology at UCLA. Brenna doesn’t really touch on infectious diseases, but he does mention briefly that, in the middle of the 14th century, you had this catastrophic demographic collapse where 60 percent of the population of Europe died. All of a sudden agricultural land is plentiful and agricultural labor is really scarce. This created a kind of crisis in the feudal system. In England in particular, it triggered a series of events that ended up with the decline of feudalism and the emergence of capitalism.

How does your research affect your teaching and mentorship role?
 

One of the key conclusions of the book is that, although advancements in medical technology over the last 50 years  – even the developments of vaccines during the COVID-19 pandemic – have been fantastic, it’s not enough on its own. If we look at what happened over the last couple of years, we see that particular groups suffered much, much more from the pandemic. They got sick at much higher rates and they died at much higher rates. And that really points to the fact that you cannot just see the pandemic as a virus spreading. You also have to think of it as a virus taking advantage of a habitat that human society has created for that virus to thrive.

The optimistic thing to take home from this is that we can look back to the late 19th century where politicians in the UK first started to tax the middle classes directly and tax the working classes indirectly to improve public health by building sewage systems pumping clean water into the cities. The past shows us that visionary politicians are capable of transforming public health and helping societies deal with the challenges that pathogens create for us. And I certainly think we can see that the political response to the pandemic in the UK and the US wasn't perfect, and that inequalities made the pandemic much worse. There are some pretty easy gains that can give us cause to be optimistic when we deal with the next pandemic.

What lies ahead for your work?
 

Oh, I’m not sure. I have to catch up on some sleep! I’m really interested in this interaction between the social world of humans and the world of microbes. So I don’t think I’ll move too far away from this topic…

Pathogenesis is published by Penguin Random House

^{Credit Book: Jonathan Kennedy / Credit Headshot: Jonathan Cole}