Back in 1676, a Dutch cloth merchant with a keen interest in microscopes, Antony van Leeuwenhoek, discovered microbes and began cataloging them. Two hundred years later, a German doctor in current-day Poland, Robert Koch, identified the anthrax bacterium, a crucial step toward modern germ theory. Those two signal advances, with others, have helped create the conditions of modern living as we know it.
After all, germ theory led to modern medical advances that have drastically limited deaths from infectious diseases. In the U.S. in 1900, the leading causes of death were pneumonia, influenza, tuberculosis, and gut infection, which combined for close to half of the country’s fatalities. For that matter, due to the threat of disease, childhood was a precarious thing more or less from the start of civilization until the last half-century.
“The world we’ve experienced since the 1950s, and really since the 1970s, is unprecedented in human history,” says MIT Professor Thomas Levenson. “Think of all the grandparents able to dance at their grandkids’ weddings who would not have been able to, because either they or the kids would have died from one of these diseases. Human flourishing has come from this extraordinary scientific development.”
To Levenson, two things about this historical trajectory stand out. One is that it took 200 years to develop germ theory. Another is our ability to combat these diseases so thoroughly — something he believes we should not take for granted.
Now in a new book, “So Very Small: How Humans Discovered the Microcosmos, Defeated Germs — and May Still Lose the War against Infectious Disease,” published by Penguin Random House, Levenson explores both these issues, crafting a historically rich narrative with relevance today. In writing about the development of germ theory, Levenson says, he is aiming to better illuminate “the single most lifesaving tool that human ingenuity has ever come up with.”
A 200-year incubation period
The starting point of Levenson’s research was the simple fact that van Leeuwenhoek’s discovery — accompanied by his illustrations of microbes we can identify today — did not lead to concrete advances for a long, long time.
“It’s almost exactly 200 years between the discovery of bacteria and the definitive proof that they matter to us in life-and-death ways,” Levenson says. “Infectious disease is a big deal and yet it took two centuries to get there. And I wanted to know why.”
Among other things, a variety of ideas, often about the structure of society, blocked the way. The common notion of a “great chain of being” steered people away from the idea that microorganisms could affect human health. Still, some people did recognize the possibility that tiny creatures might be spreading disease. In the late 1600s, the Puritan clergyman Cotton Mather wondered if specific types of “animacules” might each be responsible for spreading different diseases.
Into the 19th century, a few intellectually lonely figures recognized the significance of microbes in the spread of infectious disease, without their ideas gaining much traction. An 18th-century physician in Aberdeen, Scotland, Alexander Gordon, traced the spread of puerperal fever — a disease that killed new mothers — to something doctors and midwives carried on their hands as they delivered babies. A few decades later a doctor in Vienna, Ignaz Semmelweis, deduced that doctors performing autopsies were spreading illness into maternity wards. But skeptics doubted that respectable, gentlemanly doctors could be vectors of disease, and for decades, little was done to prevent the spread of infection.
Eventually, as Levenson chronicles, more scientists, especially Louis Pasteur in France, accumulated enough evidence to establish bacteriology as a field. Medicine advanced through much of the 20th century to the point where, in the postwar years in the U.S., vaccines and antibiotics had enormously reduced human deaths and suffering.
Ultimately, acceptance of new ideas like microbes causing disease involve “how strong cultural presuppositions are and how strong the hierarchical organization of society is,” Levenson says. “If you think you’ve shown that doctors can carry infections from patient to patient, but other people can’t entertain that insight because of other assumptions, that tells you why it took so long to arrive at germ theory. The facts of the science may win out in the end, but even if they do, the end can be delayed.”
He adds: “It can happen when a solution then gets entangled with things that have nothing to do with science.”
Science and society
Understanding that entanglement, between science and society, is a key part of “So Very Small,” as it is in Levenson’s numerous books and other works. Science almost never stands apart from society. The question is how they interact, in any given circumstance.
“One of the themes of my work is how science really works, as opposed to how we’re told it works,” Levenson says. “It’s not simply an ongoing iterative machine to generate new knowledge and hypotheses. Science is a huge human endeavor. The human beings who do it have their own beliefs and cultural assumptions, and are part of larger societies which they interact with all the time, and which have their own characteristics. Those things matter a lot to what science gets done, and how. And that’s still true.”
To be sure, infectious diseases have never entirely been a thing of the past. Some are still prevalent in developing countries, while Covid and the HIV/AIDS epidemics are cases where new medical treatments needed to be developed to staunch emerging illnesses. Still, as Levenson observes in the book, the interplay of science and society may produce yet more uncertainties for us in the future. Antibiotics can lose effectiveness over time, for one thing.
“If we want new antibiotics that can defeat bacterial infections, we need to fund research into them and market them and regulate them,” Levenson says. “That isn’t a political statement. Bacteria do what they do, they evolve when they are challenged.” Meanwhile, he notes, while “there has always been [human] resistance to vaccines,” the greater prevalence of that today introduces new questions about how widely vaccines will be available and used.
“So Very Small” has earned strongly positive reviews in major publications. The Wall Street Journal stated that “With extraordinary detail and authoritative prose … What Mr. Levenson’s book makes clear is that the battle against germs never ends.” The New York Review of Books has called it “an elegant, wide-ranging history of the discovery of microorganisms and their relation to disease.”
Ultimately, Levenson says, “Science both gives us the material power that drives changes in society, that drives history, and science is done by people who are embedded in places and times. Looking at that is a wonderful way into bigger questions. That’s true of germ theory as well. It tells you a great deal about what societies value, and probes the society we now live in.”