In his new book, “Epidemics and Society: From the Black Death to the Present,” Frank M. Snowden, a professor emeritus of history and the history of medicine at Yale, examines the ways in which disease outbreaks have shaped politics, crushed revolutions, and entrenched racial and economic discrimination. Epidemics have also altered the societies they have spread through, affecting personal relationships, the work of artists and intellectuals, and the man-made and natural environments. Gigantic in scope, stretching across centuries and continents, Snowden’s account seeks to explain, too, the ways in which social structures have allowed diseases to flourish. “Epidemic diseases are not random events that afflict societies capriciously and without warning,” he writes. “On the contrary, every society produces its own specific vulnerabilities. To study them is to understand that society’s structure, its standard of living, and its political priorities.”

I spoke by phone with Snowden last Friday, as reports on the spread of COVID-19 tanked markets around the world, and governments engaged in varying degrees of preparation for even worse to come. During our conversation, which has been edited for length and clarity, we discussed the politics of restricting travel during epidemics, how inhumane responses to sickness have upended governments, and the ways that artists have dealt with mass death.

I want to start with a big question, which is: What, broadly speaking, are the major ways in which epidemics have shaped the modern world?

One way of approaching this is to examine how I got interested in the topic, which was a realization—I think a double one. Epidemics are a category of disease that seem to hold up the mirror to human beings as to who we really are. That is to say, they obviously have everything to do with our relationship to our mortality, to death, to our lives. They also reflect our relationships with the environment—the built environment that we create and the natural environment that responds. They show the moral relationships that we have toward each other as people, and we’re seeing that today.

That’s one of the great messages that the World Health Organization keeps discussing. The main part of preparedness to face these events is that we need as human beings to realize that we’re all in this together, that what affects one person anywhere affects everyone everywhere, that we are therefore inevitably part of a species, and we need to think in that way rather than about divisions of race and ethnicity, economic status, and all the rest of it.

I had done some preliminary reading and thought this was an issue that raises really deep philosophical, religious, and moral issues. And I think epidemics have shaped history in part because they’ve led human beings inevitably to think about those big questions. The outbreak of the plague, for example, raised the whole question of man’s relationship to God. How could it be that an event of this kind could occur with a wise, all-knowing and omniscient divinity? Who would allow children to be tortured, in anguish, in vast numbers? It had an enormous effect on the economy. Bubonic plague killed half the population of full continents and, therefore, had a tremendous effect on the coming of the industrial revolution, on slavery and serfdom. Epidemics also, as we’re seeing now, have tremendous effects on social and political stability. They’ve determined the outcomes of wars, and they also are likely to be part of the start of wars sometimes. So, I think we can say that there’s not a major area of human life that epidemic diseases haven’t touched profoundly.

Were you trying to make a point about how the way we respond to these things is often a function of our racial or ethnic or religious views rather than our general humanity, and that the response has shown the flaws of human beings in some way? Or were you making a different point?

I think I was trying to make two points. I think the causal chain works in both directions. Diseases do not afflict societies in random and chaotic ways. They’re ordered events, because microbes selectively expand and diffuse themselves to explore ecological niches that human beings have created. Those niches very much show who we are—whether, for example, in the industrial revolution, we actually cared what happened to workers and the poor and the condition that the most vulnerable people lived in.

Cholera and tuberculosis in today’s world move along the fault lines created by poverty and inequality and the way in which, as a people, we seem to be prepared to accept that as somehow right and proper, or at least inevitable. But it’s also true that the way that we respond very much depends on our values, our commitments, and our sense of being part of the human race and not smaller units. When Bruce Aylward, who led the W.H.O. mission to China, came back to Geneva at the end of it and was asked a question very similar to the one you posed, he said that the major thing that needs to happen, if we are to be prepared now and in the future, is there has to be an absolutely fundamental change in our mind-set. We have to think that we have to work together as a human species to be organized to care for one another, to realize that the health of the most vulnerable people among us is a determining factor for the health of all of us, and, if we aren’t prepared to do that, we’ll never, ever be prepared to confront these devastating challenges to our humanity.

Well, that’s a very bleak thought, if I may say so, because I think it’s unlikely we are going to experience that change of mind-set.

[Laughs] I didn’t want to suggest that I’m a great optimist in this matter, but I do agree it’s what needs to happen. There’s also a dark side to humanity and that is part of the interest of this. What choice will we make? How will we go when we’re faced with this? I don’t think it’s predetermined, and a great human moral drama is being played out in front of us.

The idea of a connection between how we respond to these things and the prevalence of them is almost Biblical.

I would entirely agree with that. It really is a matter that exists at that level and is that big a part of our sense of moral imperative. I think that’s a huge part of the history of epidemic diseases.

Before this gets too dark, let me ask you a lighter question—

Yeah, I’m sorry to have such interests. My daughters protest.

Are there certain epidemics where the response has shown something inspiring about humanity?

Oh, I certainly think that. I think when I said it shows a mirror to ourselves, it doesn’t show just the dark side of humanity. It also shows the heroic side. A really good example is Doctors Without Borders in the Ebola crisis, and the way in which they put their lives and their futures knowingly, directly on the line for no self-interest whatsoever and no reward, but purely because they were committed to defending the lives and health of the weakest people in the world. And Doctors Without Borders is doing that every day in many parts of the world, and they’re even now in China confronting this.