312 | Thomas Levenson on the Mutual History of Humans and Germs

The germ theory of disease is a crowning achievement of science, up there with modern physics, continental drift, and evolution via natural selection. (Even if there will always be cranky skeptics https://www.youcanknowthings.com/germ-theory-2/.) But the road to widespread acceptance isn't always an easy one. Why did it take so long between Anton van Leeuwenhoek seeing "animalcules" in a microscope (1670s) to Louis Pasteur's work on pasteurization and vaccination (1860's)? Thomas Levenson is the author of a new book exploring this fascinating history: So Very Small: How Humans Discovered the Microcosmos, Defeated Germs--and May Still Lose the War Against Infectious Disease https://www.amazon.com/Very-Small-Discovered-Microcosmos-Germs/dp/0593242734/. Blog post with transcript: https://www.preposterousuniverse.com/podcast/2025/04/21/episode-312-thomas-levenson-on-the-mutual-history-of-humans-and-germs/ Support Mindscape on Patreon https://www.patreon.com/seanmcarroll. Thomas Levenson received a B. A. in East Asian Studies from Harvard University. He is currently Professor of Science Writing and director of the graduate program in science writing at the Massachusetts Institute of Technology. He is the author of numerous books and has written and produced a number of science documentaries for television. Web site https://thomaslevenson.com/ MIT web page https://sciwrite.mit.edu/person/thomas-levenson/ Wikipedia https://en.wikipedia.org/wiki/Thomas_Levenson Amazon author page https://www.amazon.com/stores/Thomas-Levenson/author/B001HCU6CW?ccs_id=d724e4f4-782a-4c0a-ba29-d9af618833f1 Bluesky https://bsky.app/profile/tomlevenson.bsky.social

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

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• 0:57Sean Carroll?

  Hello, everyone, and welcome to the Mindscape Podcast. I'm your host, Sean Carroll. One of the great things about the existence of podcasts as a medium, I guess it's not that different from just interview shows on radio or TV, but they're a little bit more ubiquitous now. So they provide a glimpse into things almost as they happen, right? I mean, obviously, news events can happen very rapidly, but the increase in knowledge that we get through scholarship and research happens on a relatively more leisurely time scale. And by talking to the kinds of people that we get as guests here on Mindscape, you can see science and research more broadly as it is being done.

• 1:41Sean Carroll?

  You get some interesting results, but you also get some insight into the messiness of, "We don't know the answer yet. We're still thinking about this. There's still some controversy. Let's see where we go." And it becomes pretty obvious that, of course, we're all human beings. We have our favorite ideas, favorite ways of thinking, and so forth. It's a human endeavor, science and scholarship more broadly. So it can be possible to forget that it has always been.

• 2:10Sean Carroll?

  That way, because the science that was done in the past, we receive as students and readers and listeners in kind of a finished, polished form, right? We're given Maxwell's equations or Newton's laws in notation that is much easier to understand than what they actually used. And we're given the final result after they had to go back and forth and think about lots of different things. So, things we take for granted now. The earth is round, species evolved from previous species due to natural selection. The germ theory of disease, for example. Of course, diseases are carried by germs.

• 2:49Sean Carroll?

  That's very natural. Diseases can be contagious. One person talks to another one, they carry the disease now. It makes sense that some little agent was carrying the disease from person to person. But it took a long time, as it turns out, for the germ theory of disease to catch on. And it's worth revisiting that history, both because the science is fascinating, but also the twists and turns in the human side of the story are fascinating as well. So today's guest is Tom Levenson, a longtime friend of mine. He is a professor of science writing at MIT and an active science writer, author of a number of books that I can highly recommend. The Hunt for Vulcan, about looking for that little planet

• 3:31Sean Carroll?

  that was hypothesized to exist between the sun and Mercury back in the day. Einstein in Berlin, about some of Einstein's formative years. And my favorite, which is Newton and the Counterfeiter, about Isaac Newton's life after doing science, when he became the boss of the Mint and hunted down counterfeiters in London. It was, these are human stories. What can I tell you? Newton was a pretty bloodthirsty guy, to be perfectly honest. Anyway, Tom's most recent book is called So Very Small: How Humans Discovered the Microcosmos, Defeated Germs, and May Still Lose the War Against Infectious Disease. It's a history book, a science book, a storytelling book about the various ways that we got from

• 4:15Sean Carroll?

  then Leuvenhoek, looking through a little microscope and seeing that there were critters moving around. To Pasteur saying, I can figure out how to defeat these guys. And not everyone agreeing with them along the way. In fact, some people fighting hard against them. And at some point, you have to say, a lot of lives could have been saved if people had just faced up to the scientific reality. Lessons for contemporary issues left for you to decide. So with that, let's go.

• 4:59Sean Carroll?

  Tom Levenson, welcome to the Mindscape Podcast.

• 5:02Speaker 03

  Thank you for having me, Sean. This is great.

• 5:05Sean Carroll?

  It is great, but nevertheless, the very first page of your new book kind of frightened me a little bit. You start talking about the bubonic plague in Oregon in 2024. I mean, you rush to say, don't worry, they, you know, they tamp it down because we have modern medicine now. But it did raise the question, like, how many of these old timey, terrible sounding diseases are still lurking around out there? We'll get, we'll be more systematic later in the podcast, but I just had to ask that one right away.

• 5:35Speaker 03

  Oh, um, all of them are out there except smallpox. Smallpox is the only disease, and I love this, this factoid. The only human infectious disease that has been rendered extinct in the wild. There's no more virus out there, except in a couple of freezer lockers, which is kind of nervous making that they're there. But, you know, essentially, there's no smallpox circulating, hasn't been since at least 1980. And, and that's a remarkable thing because it used to be the leading killer. And, and, you know, one in three of people who caught it would die most often. Terrible disease, but the rest of them, you know, tuberculosis.

• 6:20Speaker 03

  You know, consumption, the, you know, the, the disease that took, you know, all those figures, you know, the poet Keats and, and, and, you know, Henry David Thoreau, and, you know, everybody else, that's still causing a million deaths a year worldwide. It's not prevalent in the developed world, but it's still very much out there and it's, it's actually becoming an increasingly deadly threat. We can go into why later on. Cholera still pops up. And in fact, I saw a recent report that there's some cholera. Clearly, we know about measles, you know, there's a, as we talk, there is an still uncontained outbreak in Texas. And I understand now it's in measles cases have been identified in, in

• 7:04Speaker 03

  something, you know, 20 or something additional states. Three people have died so far in that one. And you can keep going on down the list. Polio has been on the very teetering edge of, of eradication for decades now. But it's not quite extinct. And there are cases that pop up, including in the United States, you know, as recently as 2022, 2023. And if we aren't careful, that could also break its current very narrow bounds and become a major problem again. So yeah, they're all still out there.

• 7:43Sean Carroll?

  Well, it's interesting because your book is about the historical context. You know, we have a lot of fascinating stories about how we got to germ theory and vaccines and then fighting it and so forth. But constantly, there's a refrain of, it wasn't easy. Like, the scientist invented some stuff. And then there was politics and there was like establishment pride and all those things. And you can't help but read it and go, yeah, I guess those things are still around a little bit.

• 8:13Speaker 03

  Very much so. I mean, the book, So Very Small, began as a question from an editor, like, can you think of decisive moments in science? There were these, my, my UK editor came to me, and, you know, more than a decade ago, and said, I'm doing this series on decisive moments. We're, you know, we're doing things like, you know, Picasso's Guernica, or Handel's Messiah, the first performance, that kind of thing. He says, but we have no science. What would be good idea, what would be good breakpoints in science? And, you know, so, or coffee, and I thought of a couple. And I said, well, Einstein going up the mountain in Mount Wilson, and seeing the evidence that the universe is not static, is a breakpoint. You know,

• 8:56Speaker 03

  there's, the world is different, or the cosmos is different before and after that moment. And I said, you know, I could do that, but I don't do that because I've written about Einstein a lot. Yeah. Enough. And I said, you know, I don't know anything about it, but germ theory strikes me as, as this, you know, really striking moment. And germ theory, you know, is this, this idea that was definitively established in the 1870s and 80s. And it basically says that infectious disease is not caused by some derangement of the body, or environmental disturbance, a miasma, or what have you, bad air, bad water, whatever,

• 9:38Speaker 03

  in a sort of general sense. It's caused by microbes. And crucially, each different disease, cholera, you know, typhoid, whatever it might be, battlefield infections, all these kinds of things. Each specific condition was caused by a single, specific microbe. That was an essential element of the idea. And, you know, I said, you know, before that, you have, you know, and a much looser and vaguer understanding of disease. And after it, you have this very precise definition of what's involved in infectious disease. There are, you know, it gets very precise. There are these

• 10:20Speaker 03

  things called Cox, Cox postulates, which are a list of rules about how to make sure that you have identified the correct sequence from pathogen to disease. It involves, you know, isolating the bacterium as viruses, as these were being worked out, viruses had not yet been observed. That, you know, the first ones were observed, the first one was observed in the 1890s. And, you know, so you identify the bacterium in a diseased, you know, in a diseased organism. You isolate it, you culture it, you give it to another healthy organism, and you reproduce the same disease. You know, there are these rules

• 11:03Speaker 03

  that sort of how you establish that this is in fact, the pathogen. That all happens, you know, at this, in this last quarter of the 19th century. And, you know, there's a before and after. And with that knowledge, there are all kinds of things you can do that that are, you know, also part of the story I tell in the book. You know, you have ideas about public health were already advancing in this period that I call germ theory without germs, when it's recognized that there are pathogens, but it's not of some sort, but it's not understood what they are and how they, you know, how the dynamic happens. But even that lets you do some very important things. That's the cholera story with, you

• 11:45Speaker 03

  know, and all that. But afterwards, you can do, you know, targeted public health, you understand why you're doing like clean water systems and so forth, and making sure the sewage system doesn't interact with the water supply, all these kinds of like basic, really good things. You develop vaccines. There was one vaccine that existed, Jenner's cowpox vaccine to prevent smallpox that was discovered essentially empirically or developed empirically in the late 18th century, 1790s. But there were no other vaccines. And then with germ theory, particularly pushed by Louis Pasteur in that early period, but you know, as with anything in science, lots and lots of other people are involved.

• 12:31Speaker 03

  But that's when you start getting vaccines against a much wider range of diseases. And of course, finally, third in the sequence, historically, you get chemical compounds that are discovered or developed that can attack an infection that's already lodged in the body. I mean, vaccines are sort of like the the wall around the castle, right?

• 12:55Speaker 03

  If something gets through the wall, whether it's your skin or vaccination or what have you, then you've got an infection and you do something about it. You want to do something about it. And that's where antibiotics come in. And we got all those things out of germ theory. But what really struck me as I first sort of I said, you know, germ theory, there's a before and an after and it's great. And there's a decisive moment and everything's grand. And that's all true, but you know, you and I both know that that science is not usually simply a case of a eureka moment that changes everything. Right? And so, you know, I started looking into it a little bit more. I mean, I told my editor that he should find somebody who actually knew about medicine and the history of

• 13:39Speaker 03

  microbiology and all that sort of stuff to write it. And then, you know, I had I wrote two other books while this idea was still, you know, bouncing between us. And finally, he said, you better write it. And I said, okay, I better write it.

• 13:53Speaker 03

  And, you know, along the way, I discovered something that turned it into a book that really sort of spoke to the way I think about the world. And that was, you know, it should have been obvious at the time, I guess, but it took me a while. I'm slow. It took me a while to get there. The

• 14:12Speaker 03

  Microbial world, there is actually a decisive singular moment when it was discovered.

• 14:19Speaker 03

  You know, microbes are not visible with the naked eye. You needed to develop instruments. The instrument in question is the microscope. That comes about early in the 17th century. And people look at all kinds of things with it, but they don't, you know, partly because the early microscopes weren't that powerful and partly because, you know, it just, it takes a while to realize that, you know, with this instrument, it's not just that you can see more detail on things you already know are there, right? You look at a bee's wing and so forth. One of the very famous early books is, you know, is a microscope, you know, sort of reports on microscopy is this On the Life of Bees that was, that was written by two Italians. And there are these beautiful drawings of

• 15:03Speaker 03

  these magnified insects and it's really cool. But that really took a step forward when Anthony van Leeuwenhoek, and I hope, I apologize to my Dutch friends for my butchering that, but he was a Dutch cloth merchant, a draper in, in Delft. And, you know, cloth merchants of time used lenses to, you know, inspect the fabric for flaws or whatever. And he became interested in that, you know, that magnified world. And he almost certainly saw a copy of Robert Hooke's Micrographia, which was in some ways the first great popular

• 15:47Speaker 03

  science text. This book of magnificent microscopics, microscope studies of both, you know, materials, you know, points of needles and so forth, but lots of living things. But again, you know, he had pictures of a flea and the compound eye of insects and so forth. He saw in greater detail things that were again, you know, perceivable by, you know, in some ways by human eyes and didn't penetrate deeper into the, into the invisible realm, you know, invisible to us.

• 16:20Speaker 03

  And that seems to have inspired Levenhoek. And he became, it turned out, he was a meticulous craftsman. He made these great, single-lens microscopes, these little drops of glass, that were incredibly powerful for the day. He was almost certainly making the most powerful instruments in Europe at the time. And this work of his started 1673 or so, and by 1676, he was really sort of feeling his oats and pointing this, his instrument, or using his instrument on a wider and wider range of subjects.

• 17:01Speaker 03

  And he looked at a drop of pond water. And in that pond water, he saw what he called anemaculae. Anemoculae, little ants.

• 17:14Sean Carroll?

  I love the name, yeah, that's great.

• 17:16Speaker 03

  And he saw some things that are probably planaria or other fairly large, multicellular microscopic organisms. But then he looked long enough and hard enough, and his microscopes were good enough, that he actually saw single-celled bacteria. And we know he did, not just because he reported and described it, and you can see descriptions. But I think the earliest surviving of his drawings, he was a meticulous draftsman. He drew pictures of lots of stuff that he studied. Comes from 1682, and there are four or five bacteria drawings on it.

• 17:58Speaker 03

  And they are present-day identifiable as, at least to families of bacteria, if not the specific strain. And those experiments have been replicated. Historian of science, he made a single-lens microscope and did it again, and he said, yes, he could have seen what he said he saw. So, yeah, he really saw bacteria. And again, he saw them for the first time in 1676, and then he kept observing them. And one of the really interesting things to me is, within a very few years, he looked at it in pond water, he looked at it in other liquid sources. He infused peppercorns in water, and they, because he was interested to see what would happen with peppercorns,

• 18:43Speaker 03

  but he also saw microbes there. But at some point, he took gunk from his, between his own teeth, and looked at that through the microscope and saw more bacteria. And why is that significant? At least it's significant to me. And the answer is because that's when, you know, that's the first recorded example of recognizing that microbes live inside us.

• 19:06Sean Carroll?

  Yeah.

• 19:07Speaker 03

  You know, gunk between teeth is not very far inside us, but still, you know, it's there. And we can, we can, you know, cohabit in the literal sense of the word with this whole microbial universe.

• 19:22Sean Carroll?

  That might have been a eureka moment, but it was certainly also a very creepy moment, don't you think?

• 19:26Speaker 03

  Oh, yeah. I mean, it's, it's, but what's interesting is, so, so the question for the book was, all right, that's 1676 and the Robert Koch's demonstration that anthrax is caused by a bacillus b. anthracis, a single microbe, which was the first, you know, end to end account of, demonstration that, you know, anthrax is caused by a pathogen, it's this pathogen, and you can replicate it and it's a living, you know, microbial, you know, it's a bacterium. All that was set, you know, Koch did that from two or three days before Christmas in 1876

• 20:09Speaker 03

  to, you know, two or three, you know, two or three weeks into January, he'd created a chain of infection with these, you know, he takes some b. anthracis, give it to a rabbit. Then when that rabbit got sick, he'd harvest blood and isolate the bacteria again and give it to the next rabbit and he created this chain of infection and he isolated the, the bug and did all those, and even also traced the life cycle of anthrax, which, you know, he caught them in their spore stage and he was able to activate, you know, motile bacteria from, from the spores. He nailed it in the space of three to four weeks. But that's 200 years after von Levenhoek.

• 20:52Speaker 03

  And while it is, I think, formally impossible to say with certainty why something doesn't happen.

• 21:01Speaker 03

  That's still a long time. And I wondered why it was so long. Right. What were the impediments to figuring that out? And that's really where the book got started. And what became exciting as I wrote the book is it became clear to me at least, and I hope I persuade readers, is that the broad outlines of why it was difficult to go from the first observation of microbes to recognizing that they actually matter to us in really important ways, helps, that lens helps us understand why we're currently in trouble with infectious disease, why many of the advances of the last century and a half are now at least at risk, if not, you know, already really compromised.

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• 22:44Sean Carroll?

  Maybe you can help us understand what would have been the mindset of the people in the pre-germ theory area, era. You've already mentioned miasma theory, but we knew that disease was infectious, or at least infectious diseases are infectious. I'm guessing that people had ideas about how diseases were spread, either by touch or breathing or whatever. Was there some consensus as to what they thought happened before they said it was little microbes?

• 23:17Speaker 03

  Well, that's, I mean, for, you know, sort of for the philosophy of science, that's what's so interesting about this case, right? How does a theory get replaced? Well, there, you know, there's the big broad outlines and there's, you know, you can turn to Thomas Kuhn and you can turn to people who've argued with Kuhn or whatever. But something that I've, I really think is true in a bunch of different

• 23:41Speaker 03

  domains is that the easy conventional sort of high school version that, that theories change when a fact comes along that the theory can't accommodate.

• 23:53Speaker 03

  You know, that's, that's tricky on so many levels. And we can talk, we could talk a lot about that if you wanted. But the problem for make, one of the problems for making the connection between microbes and disease is that there was already a pretty

• 24:15Speaker 03

  coherent theory of disease that just, that, that didn't, you know, particularly predicts things, but it accurate or it adequately described what was observed. So when you have something like the plague,

• 24:34Speaker 03

  you know, there's sort of, there, there were two questions. What, what is a disease? You know, what's happening when you get sick? And how does a disease move from, from one person to the next? Those are, those are obviously related questions, but there, but there, you can, you can distinguish between them.

• 24:53Speaker 03

  And there were a variety of detailed accounts of disease. And certainly the more people observed different conditions, people recognized the plague as something other than other fevers that, that, that you might, that you might encounter. And in part, they recognized it because the plague has some characteristic, you know, markers like, like the buboes of the, of the buboes of bubonic plague, these, these lesions that, that burst on your skin and so forth. And even though they, you know, that's not a universal symptom of the plague, it's common enough that it, you know, there are ways to, to, to recognize it as the plague and not as, you know, what we would now call typhoid or something else. Now recognized as typhoid.

• 25:39Speaker 03

  But the, you know, so there was, there was some, you know, I mean, people, people in the past are not dumber than we are. They have less information or different information, but they're not, you know, stupid. And so there were detailed observations and people obviously wanted to know what was going on when you had a terrible event like the plague. But the, the basic idea is that there is, you know, that healthy bodies are in a form of balance. You know, there was humoral theory, the four humors that have to be in balance. But there are, you know, sort of other broader, you know, you could, you could sort of generalize that. You didn't have to be a Galenist and say, no, it's, it's, it's the humors. There were, there were, you know, what were called chemical physicians, which were people who

• 26:23Speaker 03

  are looking at, at, at more detailed accounts of, of, you know, the substances that make us up. And people were beginning to be aware of bodily systems. I mean, this was, you know, William Harvey working out the system of blood circulation is not just important for that one story. It, it sort of gives you a way to think about how the body works that, that, that was distinct from what went before. But overall, the idea is, you know, when you're healthy, your body's in balance and, and ill health is some derangement of that balance. And if you think about it, you know, as a, as a sort of broad statement, you know, that's, it's still true.

• 27:03Sean Carroll?

  It's a metaphorical way of talking about what's going on. Yeah.

• 27:06Speaker 03

  Look, you know, think about diabetes. It's, it's a problem of insulin regulation. Well, when you're, when your insulin regulate regulatory system is working as it should, you know, you don't have diabetes and when it isn't, you do. That's a form of imbalance. It's still a, you know, it's not a, it's not a crazy concept. It's a perfectly understandable one. And, and it adequately described what was observed with the naked eye. And similarly with the spread, the origins, you know, where does the first case come from? And then how does it spread? There were, you know, a range of possible sources. I mean, ultimately the source was God. God.

• 27:45Speaker 03

  Had was expressing judgment on individuals or societies. And this judgment, you know, the, you know, the judgment was expressed through the events that happened to you in life, including illness. But, you know, it was well established that people live in the material world and divine judgments and the devil's blandishments, et cetera, occur through natural means. There was a scientistic approach to understanding both, you know, satanic and divine regulation of the world or interaction with the world. And so you look for things like, and, and, you know, that's where miasmas come in.

• 28:27Speaker 03

  It's, it's, you know, literally bad air. It could come from an emanation from the earth. It could be, you know, the foulness of, of, you know, in a, you know, as you, as you move forward in time, the idea is that the bad city conditions, unhygienic conditions produce these miasmas that are deranging. You don't need to have some sort of supernatural or origin for these things. They can be perfectly straightforward. And again, you know, when you think about it, and this is, this is sort of skipping ahead in the book, this is where some of the critical ideas of the 19th century came in. You don't need to know about germs specifically to, to recognize the correlation between, you

• 29:11Speaker 03

  know, fetid odors and decaying flesh and so forth as not great things to, you know, raise your kids immersed in. So you have all this knowledge and you have a persuasive, and the great thing about miasmas is you don't have to invent a mechanism for carrying them from place to place because if it's in the air or if it's, you know, somehow in the environment, it can move from person to person. And you know, there was the idea of contagion, which you know, comes from the root to touch. You know, so obviously handling somebody diseased was understood as a risk for the for the person doing the doing the work.

• 29:52Speaker 03

  But also contagion as a concept sort of grew more indirect. I mean, I I had the I had the image in my head of the old 1950s early slush box automatic transmissions. You know, the hydronic where the gear changes are carried through water. You know, you don't actually have a a direct mechanical connection between bits of metal. You know, the idea of early disease contagion being kind of hydramatic contagion.

• 30:20Speaker 03

  Sorry, struck me as a as a sort of plausible metaphor. But all that, you know, you can you can look at the Great Plague of London, which is sort of where the the book proper starts. And you've got a sufficient explanation.

• 30:38Speaker 03

  Now, you did have people who were looking both for specific treatments that might actually help with the the plague. And they had, you know, no idea and the things that were proposed were ineffective, though in some cases may have made people more comfortable when they were asked to drink more alcohol or something.

• 30:57Speaker 03

  But you also had, you know, some attempt to think about what kind of substance, what seeds of disease in the language of the time might be going from, you know, what was in the miasma, what was the, you know, the active ingredient, as it were. And again, you know, all that is is fully plausible and you can you can squint just right and see in this concept of seeds of disease, seeds of disease, a precursor, something, an idea that could lead you to microbes.

• 31:31Speaker 03

  But there was nothing in the thinking of the time that required them. Right. And there was no indication that whatever these seeds might be, you know, they could be, you know, inert, they could be, you know, they could be sort of gaseous, they could be almost anything, right? There's no no pointer to towards, you know,

• 31:53Speaker 03

  some specific identifiable, you know, living element.

• 31:59Speaker 03

  Of course, during the Great Plague of London, this was, you know, 10 years before Levenhoek first saw microbes. But, you know, there were diseases that went, you know, diseases didn't stop in 1676, obviously.

• 32:10Sean Carroll?

  But this is something that's interesting that comes out in the book. It is quite a span of time in between van Leeuwenhoek and then the acceptance of the germ theory of disease. But not only were people fighting disease at the time, they were doing so, at least sometimes, in ways that, in retrospect, make perfect sense if you believe the germ theory of disease. So, in the book, you talk about, John Snow is a famous guy, Florence Nightingale as the nurse, and a lot of modern methods of being clean and well behaved. But the one I have to ask about, since we don't have infinite time, is Cotton Mather, who is more famous for other reasons, but apparently, he was quite the experimental medical doctor.

• 32:54Speaker 03

  Well, I wouldn't, he's more of an eager magpie than an actual rigorous experiment. I mean, he, so Cotton Mather, of course, is a Puritan minister. He's most famous for his role in the Salem witch trials, in which he deeply believed in the truth of the testimony of those who are accusing people of being witches, and believed in, in sort of dream evidence. I dreamed this happened, and, you know, thought that that was how Satan would communicate. And was thus directly implicated in the deaths of a lot of people who were

• 33:35Speaker 03

  clearly, you know, shouldn't have been killed. And at the same time, you know, and he was part of this, he was not just a Purit, any Puritan minister, he was, you know, if there can be such a thing, he was part of the Puritan aristocracy. His father and uncles, and, I mean, his whole family was basically in the business of being Puritan leaders.

• 34:01Speaker 03

  You know, he's a very funny character. He apparently, when he was a student at Harvard, back in the day, he apparently had some inclination to become a doctor, to study medicine. But of course, the pull of the family business was too strong.

• 34:19Sean Carroll?

  The family business being a minister.

• 34:22Speaker 03

  Yeah, exactly. He was ordained in and gave his first sermon at his father's church, which was the leading church in Boston. When he was ordained, something like 20% of the population of Boston was in the audience. I mean, he was like, you know, he was a big deal. His family was a big deal in that line of work. But he was clearly also both intellectually ambitious and interested in the natural world. And so, you know, 20, 30 years after the witch trials, he started writing to the Royal Society in London with these sort of American curiosities. And some of these things were just bonkers. Remember, the Royal Society early on was itself,

• 35:09Speaker 03

  ranged from this incredibly serious, important stuff to, you know, you look at it and you laugh. I mean, Robert Boyle, the great, you know, sort of patron saint of chemistry, very early on in the Royal Society's history, read a paper to the assembled fellows about a monstrous calf. You know, I mean, it ranged, truly, their interests ranged all over the map. And Mather presented these sort of American wonders, some of them very, you know, very real, interesting bits of natural history. Some of them, these sort of legends that he seems to have accepted credulously. And the Royal Society loved him and published him and made him a fellow of

• 35:49Speaker 03

  the Royal Society. And he was also, really, as part of his ministry, as much as and his intellectual life, very interested in all things related to medicine and health. And he collected anecdotes, he collected recipes that people, you know, had for, you know, cures or nostrums. And

• 36:15Speaker 03

  He really, I think, had a sense that it was sort of his duty as a minister and essentially a representative of God on earth to do what he could for, you know, the health and well-being of both his community, but sort of, you know, by communicating with the Royal Society or whatever, the world at large. And, um, and he was, in fact, genuinely one of the pioneers of vaccination, being, uh, being, uh, one of the earliest proponents of smallpox inoculation, or variolation, as it's sometimes called, where you take smallpox material from somebody

• 37:00Speaker 03

  who's suffering from a hopefully mild case of the disease, and you scratch, you know, scratch marks into a healthy person's arm or arms, they often did it in multiple limbs, uh, and you mix this stuff in, and the idea is to give the person a mild case, a very, hopefully very mild case of smallpox, and thus confer on them what had already been observed to be the result of a smallpox infection if you survived, which was lifelong immunity to any further, uh, cases of the disease.

• 37:29Sean Carroll?

  And it's not literally vaccination. You've not, you know, developed a vaccine, but inoculation is sort of the broader category of which vaccines are an example.

• 37:38Speaker 03

  Right. And it's, it's, it's, this is the, uh, earliest attempts in Western Europe and the Americas to engineer immunity to a naturally occurring disease. And that's, that to me is the distinction that's key.

• 37:52Sean Carroll?

  Yeah.

• 37:52Speaker 03

  Because vaccines are a particular way to engineer that, that immunity.

• 37:57Speaker 03

  Mather learned about this technique first from his slave, uh, an African man who had been gifted to him by members of his congregation, who, uh, who told him about undergoing this procedure in Africa. And then when in the mid seventeen teens, the Royal Society published two papers from doctors working in the in the in the Near East, in Turkey. And one was from definitely in Turkey. I'm trying to remember where the other one was working. I can't can't off the top of my head. Anyway, that also described the use of this, you know, inoculation, smallpox inoculation in Turkish medicine.

• 38:42Speaker 03

  Mather wrote to the Secretary of the Royal Society, having seen this paper and said, you know, I can attest that my servant, as he called him, his slave, had had already told him about this and that he followed this up with conversations from other people with knowledge of Africa. And that this seemed to him such a promising, promising preventative for this, you know, really deadly horrible scourge of a disease that that should smallpox visit Boston again, he said, I will attempt to, you know, get this method used. And sure enough, a few years later, in seventeen twenty one, smallpox comes back to to Boston.

• 39:25Speaker 03

  And Mather tries to persuade Boston's medical community to do inoculation. Only one member of that community agrees to do so. Others vehemently oppose him.

• 39:38Sean Carroll?

  A common theme in the book, like we said.

• 39:40Speaker 03

  Right. Well, and the interesting is they oppose him for multiple reasons. One, there is, you know, certainly there's risk and there are dangers involved. You're doing, you know, the Human Subjects Committee might have had some words to say, right? But the other reason is, is, you know, this was a proxy for a battle over power. You know, you know, sort of professional power, who who had the right to do medicine? You know, not Puritan ministers, god damn it. You know, there was one European trained M D in Boston at the time, who bitterly resent, clearly bitterly resented the incursion into his prerogatives. But also was more broadly part of a broader power struggle in Boston.

• 40:22Speaker 03

  Where a number of people up to and including, you know, James Franklin, Ben Franklin's brother, who was the publisher of the first independent, non-censored newspaper in the in the colony, were saying, you know, we've got to reduce the influence of Puritan ministers. And this is a this is a club to beat, you know, Mather with, and by extension, the Puritan establishment.

• 40:47Speaker 03

  And so there was this significant resistance up to the point of a direct attack, you know, on Mather's life. Somebody threw a bomb through his window, which fortunately didn't explode. But, you know, no joke.

• 41:01Sean Carroll?

  Yeah.

• 41:02Speaker 03

  And so ultimately, they were able to inoculate a few hundred Bostonians with with almost entirely good results. While several thousand Bostonians got sick and something like 14% of them died.

• 41:25Speaker 03

  And, you know, the question was, those were lives that could have been said, saved.

• 41:30Sean Carroll?

  Right. So the inoculated people essentially all survived?

• 41:35Speaker 03

  Essentially, there's there's a bit of controversy because a few died. And the question was, were they already ill or had they died of something else?

• 41:42Sean Carroll?

  Sure.

• 41:42Speaker 03

  And the person who was doing the inoculation said, yes, they were all, you know, it wasn't me. And, you know, it's it's it's hard to say exactly, but the proportion of people who suffered serious, yeah, a huge proportion of Boston got sick. Of a substantial chunk of them, and it was a relatively mild strain of smallpox, clearly because a 14% death rate was below the average. But still, that's, you know.

• 42:08Sean Carroll?

  A lot of people.

• 42:09Speaker 03

  Yeah, I was, you know, Boston was under 10,000 people. I think, again, I'm pulling, I should look at the book right now. Something like 900 people died. So it's, you know, that's a big chunk of Boston, right?

• 42:20Sean Carroll?

  Yeah.

• 42:22Speaker 03

  And.

• 42:24Speaker 03

  You know, and the objections to this inoculation campaign were sort of the prototype for what would come after. Some legitimate medical concerns and a lot of other stuff going on at the same time. Political issues, cultural reluctance to, you know, attempt whatever was going on. Specific social enmity.

• 42:48Sean Carroll?

  Right.

• 42:48Speaker 03

  You know, all those things mix in. And that's not what you think of usually as an explanation for why some scientific event doesn't happen.

• 42:56Sean Carroll?

  You do if you've read some science. You do if you know a little bit about the history. So that's not surprising to me.

• 43:01Speaker 04

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• 43:32Sean Carroll?

  Speaking of personalities and conflicts and things like that, let's leap forward to the real germs. And Louis Pasteur, I guess, is the first person to talk about. Obviously, from your book, I get the impression that on the one hand, he deserves as much credit as he gets. He really did do a lot of other things. On the other hand, just like the more familiar examples to me of Newton and Leibniz, there were rivalries and jealousies and bitter priority disputes going on.

• 44:01Speaker 03

  Absolutely. Just to put a mark in, I hope we can cycle back to the story of childbed fever. Because that's a really classic and important case in this, you know, I think it sets up some of what we're seeing now.

• 44:16Sean Carroll?

  We can talk about childbed fever. Let's do it. Yeah. We're not going to run out of electrons.

• 44:20Speaker 03

  Okay. So childbed fever, Pierre-Paul fever is a, is an infection. There are actually a number of different bacteria that can produce its symptoms. And it happens to women who have just given birth. And it can be devastating. I mean, it's very frequently fatal. And

• 44:47Speaker 03

  What's interesting is there's a whole sort of social history dimension to it. Purple fever is described in, you know, ancient Pythagorean texts even. So people knew about it in antiquity and it, you know, clearly is a disease that didn't just pop up in Europe in the 16th, 17th century. But there was a change that happened. Up until, you know, sometime in the 16th to 17th century, childbirth had been largely the province of women, you know, it's handled by midwives or, you know. And, you know, it's very local.

• 45:31Speaker 03

  So if, you know, you wouldn't have in a village 12 women giving birth in the same week, right? You know, that's not usually how it worked. And reports of purple fever are sparse from that period. And partly they're sparse because, you know, this was not, you know, that community was not a writing community. There weren't journals of midwives and so forth and so on. But in the, as, you know, European cities grow and power centralizes and you have things like increasingly formal associations of medical, you know, of experts in some sense,

• 46:16Speaker 03

  doctors, childbirth becomes increasingly sort of overtaken by male doctors. And at least in the cities, happens in hospitals where you get, you know, you do get a lot of women in the room at the same time giving birth. And that's when you start to see not just individual cases of purple fever popping up from time to time, you know, bad luck, there's, you know, so the wrong bacteria happened to be in the lying in chamber, you know, that could happen. But when it happens in a, in a lying in hospital.

• 46:53Speaker 03

  You have, you know, you have the perfect conditions for the bacteria, the pathogens to move from patient to patient. And that's what happened, you know, as very early on in the history of the hospital, you have, you have stories, you have reports of essentially epidemic purple fever.

• 47:13Sean Carroll?

  The problem with hospitals is they're full of sick people. It's a terrible place to go.

• 47:18Speaker 03

  They're, they're full of sick people. And, um, you know, if you have a person, you know, delivering, you know, attending a delivery, uh, and then, you know, wiping their hands off and moving on to the next person, uh, you can see where the problem might arise, right? So you, um, uh, so over the course of the 17th and 18th century, there are repeated reports of outbreaks, you know, of purple fever where, where dozens or more women will, will, uh, suffer and many die, uh, from this condition. Um, and, you know, you start seeing like conditions, you know, you might have sort of a two or three year run where there's just this, you know, ongoing transmission of purple fever.

• 48:03Speaker 03

  And again, up, there were a whole bunch of different theories, uh, adduced as to how this might happen. It didn't appear to be a contagious disease, right? Cause you know, if, if, if a woman in a, in a hospital falls sick and then, you know, a woman in a, in a, in a home falls sick, um, unless you notice that the same person attended both births, it doesn't appear that there's any connection, right?

• 48:31Sean Carroll?

  Right.

• 48:31Speaker 03

  The two people don't touch each other, all that sort of stuff. So there was, there was no urgent need to try and identify a, um, a, a sort of course of causation, right? But, uh, you know, people did notice that these were, that, that, the sort of explanations for how, um, some derangement of how the milk was being expressed or other, other issues that might, uh, attend a difficult childbirth. Um, you know, that, that was, that didn't really explain why you'd get clusters of cases in a place and time.

• 49:11Speaker 03

  And so in 1795, you know, well before, you know, the conventional story is this is all worked out in the 1840s in Austria. But no, in 1795, this doctor in that, you know,

• 49:24Speaker 03

  you know, well-known center of medical research, Aberdeen, Scotland, in 1795, a local doctor

• 49:38Speaker 03

  started delivering babies and and took notes on the midwives who were who were delivering babies. And there was this ongoing chain of infections and people suffering and dying of purple fever. And, you know, he tried a couple of different explanations. He looked at weather reports to see if there was a correlation with weather conditions. I mean, again, there was no, you know, base of knowledge or theoretical insight that drove this purely empirical, what's going on? So he looked for correlations. And eventually, he started noticing that there was not, it didn't take him that long. He started noticing that there were sequences of infection. Both he and the midwives would go from patient to patient to patient, and those patients would

• 50:23Speaker 03

  in sequence come down with with this, you know, terrible debilitating, too often fatal condition. And he wrote it up. And he said, basically, you know, we're the cause. And he didn't say it basically, he said it explicitly. He said, you know, it shocked him to realize that he had been the source of his patient suffering. And, you know, he he wrote this and published it in 1795. And nothing happened.

• 50:53Speaker 03

  He was basically driven out of town. The midwives were furious at him for suggesting that they might be killing their patients. It didn't get picked up in London.

• 51:02Sean Carroll?

  So something happened, but not not acceptance of his ideas.

• 51:06Speaker 03

  Yeah. And and, you know, a few years later, he died of, I think tuberculosis, and was basically lost to history.

• 51:14Speaker 03

  And you know, there's no, you know, but the idea was there and the not, you know, if you looked at that and you could say, okay, there is something that is moving from patient to patient on the doctor's hands or on the midwife's hands. And we need to interrupt that. You can, you can, you could, that was not a difficult leap to make, but it didn't get made.

• 51:36Sean Carroll?

  And science didn't know about microbes at that era.

• 51:38Speaker 03

  They did not, they knew about microbes existing.

• 51:41Sean Carroll?

  Yeah.

• 51:41Speaker 03

  They did not connect them with diseases.

• 51:43Sean Carroll?

  Right.

• 51:44Speaker 03

  Just, I know we're sort of looping and looping. One of the most interesting things in the book, one of the things I found most surprising was that Cotton Mather, in the 1720s, you know, Cotton Mather, Witchburner, actually wrote down a suggestion that Levan Hook's animaculi, animacules, might be the cause of diseases. And he even got, you know, different animacules could cause different diseases. This was, you know, he wrote it down, the book he wrote it down in was a manuscript at his death and wasn't actually published until the 1970s. But there, and he almost certainly derived the idea from

• 52:26Speaker 03

  somebody else, a doctor who wrote in this one brief mention in a, in a British paper. And again, these ideas were thinkable. People could imagine it clearly. We have, you know, we had that absolute existence proof, right? But it struck no chord and the idea essentially disappeared for well over a hundred years, which is still to me, I mean, I, I have, I try to explain it. I think I do explain it. But when you just stop and think about it for a minute, it's, it's mystifying and incredibly saddening when you think about how much loss and pain and suffering derived from the fact that nobody picked up on that.

• 53:03Sean Carroll?

  Well, there's a lot of ideas in the history of science that nobody picks up on, but here's something where it's kind of obviously important to make progress on this. And you might hope that people are responsibly searching around for every possible hypothesis to go test.

• 53:23Speaker 03

  You would. And I mean, one of the things to, to, if, if people listening to this take one thing out of it.

• 53:33Speaker 03

  The truly remarkable thing that Levenhoek did is he revealed not just more information about something, but a whole new realm of, you know, material existence that no one had suspected existed before. Hmm. You know, up until that moment, we didn't know about the microbial world, the microcosmos. And it's there, and we now know how incredibly rich and important it is and how, you know, deeply embedded in the history of life on Earth and, you know, all the different things we can now say about microbes. But it's...

• 54:14Speaker 03

  It seems to me analogous to the impact that we would feel if we got definitive proof of life on another planet. Right. You know, it's that revelatory.

• 54:28Speaker 03

  And, and you would have thought that that would have led to more speculation. I mean, again, to sort of push the analogy, think of all the writing from people, you know, in, in the 19th century and on about life on other planets. You know, the very, you know, that very early movie of the Lumiere Brothers' journey to the moon. I mean, the idea of, you know, clearly the existence of other worlds beyond our own is enormously stimulating the imagination. Well, here was a whole nother world, wholly unsuspected, teeming with creatures that are unlike the creatures we see with our naked eye, that have different shapes and

• 55:09Speaker 03

  different means of locomotion, that have, you know, apparently whole, you know, societies, ecosystems, interactions going on, that have been there all along, beyond the limits of our, of our senses, and now they're there. I am a little perplexed why that wasn't crazier, right? You know, why that didn't, why that didn't

• 55:29Sean Carroll?

  Yeah.

• 55:30Speaker 03

  make people jump more.

• 55:31Sean Carroll?

  Yeah.

• 55:32Speaker 03

  But just as, I mean, I know I rabbit on too long about such stuff, but just to sort of round off the purple fever story, flash forward to Boston in the 1840s, Oliver Wendell Holmes, senior, mediocre poet, Boston Brahman, and medical doctor, at that point, a young medical doctor. And he, at a meeting of a local medical society, somebody raised the question about how you can explain a then ongoing purple fever outbreak. And Holmes took it on himself to try and study it. Unlike this doctor in Scotland, Holmes was not, you know, he didn't

• 56:15Speaker 03

  have an OB practice, he wasn't delivering babies. He was a young and relatively inexperienced doctor at that point. And he just did this from the records, you know, case records. And he tracked this, tracked the births, cases of purple fever, deaths, and attendance. And he, you know, in a relatively short period of time, he reported back to the medical society that, yeah, in fact, there are patterns of infection and the common element is the doctor. And, you know, what needs to happen is the doctor has to make sure, or the midwife, I mean, the medical person attending the birth, needs to make sure that they are, you know,

• 56:57Speaker 03

  fully cleansed of, you know, whatever's going on between births. And he published this, as well as giving it as a society talk. And again, not only did sort of nothing deeply change, he got a severe and, you know, actually contemptuous pushback from established, you know, senior American OB-GYN practitioners. And the one that really stuck in mind was this, you know, perhaps the top such doctor in the US at the time, a Philadelphia doctor named Meigs or Migs, M-E-I-G-S, again, I'm not sure how it, how it was pronounced,

• 57:43Speaker 03

  responded that it was, you know, that, you know,

• 57:47Speaker 03

  That Holmes writing was the monderings of a sophomore and that what he concluded couldn't be true because, and I quote, "A gentleman's hands are clean."

• 57:58Sean Carroll?

  There you go.

• 57:59Speaker 03

  Q E D. Right. And then, you know, the story sort of concludes with the, with the most well-known one, which is Ignat Semmelweis, working in the Vienna General Hospital with the two wards, where there's one ward handled by midwives who do not do pathology, do not dissect the bodies of women who have died of purple fever, and the other ward run by doctors and male medical students who do, in fact, you know, this is part of the great transformation of medicine into a science. You do pathology, you study the diseases in the body by dissecting and analyzing the corpses, and you know, mostly this was this enormously rigorous and productive advance in the way you teach and think about medicine, it leads to all kinds

• 58:43Speaker 03

  of good stuff, but not here. So, you know, you dissect somebody who dies of purple fever, and guess what you have on your hands and body and clothes if you're not, if you don't sterilize yourself. And so, lots and twists and turns in the story, but Semmelweis figures out that this is, this is the meaningful distinction between the two outcomes. The, the midwives ward has a very, very low rate of purple fever, and as many as 10% of the patients in the other ward fall victim to it. So it's, you know, it's a big deal.

• 59:19Speaker 03

  And he says, okay, we're going to stop this. He puts a chlorine solution that, you know, next to the autopsy room and says, you can't go back to the ward until you wash your hands thoroughly, until there's no smell left. You know, again, didn't know about germs, he didn't know what it was. He just said, there's these, you know, cadaverous particles. And you got to, you know, they're associated with death, so you've got to wash the stink of death off you. And that turned out to be enough, you know, long enough, enough sterilization, so that the, you know, when, when that was done, the doctor's ward very rapidly approached

• 59:59Speaker 03

  the same levels of, of infection that the midwives had already achieved. So it was, you know, again, he had no idea what, just cadaverous particles. He had no idea what was causing the disease, what the pathology of the disease was, how it developed, what the, you know, chemical biochemical mechanism, none of that. All he knew is that when medical students and doctors walked from cutting up a corpse to delivering a baby, bad things happened. Let's stop those bad things, right? Let's just put a wall between them. And again, you know, the tragedy is he was not, though, though he got, his ideas got some traction in some places. Broadly, his conclusions were rejected, both within the German-speaking world and, and,

• 1:00:44Speaker 03

  and beyond. And it took, you know, several more decades before the idea of proper sterile conditions really took hold.

• 1:00:56Speaker 04

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• 1:01:56Sean Carroll?

  Well, and when Pasteur does eventually come along and sort of put things together and, and put the germ theory on a proper footing, um, his inspiration or his route into it was not through trying to cure diseases, right? That was a clear, clear thing to try to do, but he was just trying to make sure that you made wine correctly and reliably.

• 1:02:17Speaker 03

  He did refer to, it was sort of a term of the time, diseases of beer and wine.

• 1:02:24Sean Carroll?

  Okay, good.

• 1:02:25Speaker 03

  Metaphor clearly in his mind. But yeah, his, you know, the first real demonstration of a, you know, of a bad thing happening because of the metabolic, the metabolic work of a, of a bacterium was Pasteur's study of making beet juice. So he had, when, this was in the 1860s, he had a, maybe it might have been late 1850s, excuse me, I misspoke.

• 1:02:58Speaker 03

  He had a student, he was a young professor of chemistry. He was not a biologist, and he was certainly not a physician.

• 1:03:06Speaker 03

  He was teaching chemistry at the University of Lille, and one of his students was the son of a local manufacturer who made beet alcohol, among other products. And they were having a bad run at the time where, you know, instead of producing alcohol, they produced this foul smelling useless substance. And, you know, they wanted to know why. And Pasteur agreed to take a look. And eventually identified a lactic acid bacterium. So instead of, you know, yeast metabolizing sugar and water into alcohol, you had lactic acid bacteria metabolizing their inputs into this foul smelling, nasty, industrially useless lactic acid, hence the name,

• 1:03:51Speaker 03

  within the beet juice. And he was able to say, basically, you want to make sure your, your, your vats of beet juice are free of these bacteria before you go in and, you know, gave them some insight into industrial processes. But that was the first insight where he saw that, two things really, that bacteria free floating in the atmosphere, microbes free floating in the atmosphere, could reach and, you know, affect substances like.

• 1:04:22Speaker 03

  Beer, wine, beet juice, soup, whatever. So there's this notion that there is this, you know, potential pathogens that we are surrounded by all the time. And that these microbes actually do have meaningful, large-scale, physical effects on, you know, the scale that human beings occupy. And there are a whole series, I mean, he did, there was, that insight took him in a bunch of different directions. It included, you know, finally, you know, his, often regarded as the definitive and final destruction of the concept of the spontaneous generation of life.

• 1:05:05Sean Carroll?

  Right.

• 1:05:06Speaker 03

  And, but it also took him through into a bunch of different aspects of, of infection and this sort of just microbial role in biochemical processes more generally.

• 1:05:19Sean Carroll?

  Well, that's what I learned from that part of the book was that, you know, an important aspect of it, because it's always hard when we know or we think we know now what is going on, like, why didn't they know? It's not that hard. But the existence of the microbes was known, but the idea that they could have an effect was less clear, right? Like, you know, people thought that for the wine thing, there were chemical reactions, sure. But the idea that these little beasties are contributing to those chemical reactions was apparently a little bit of a barrier.

• 1:05:49Speaker 03

  It was, yeah, it took a long time. I mean, it took a long time even to associate yeast with, with the fermentation. And then the idea that you have yeast that are doing fermentation, but these bacteria, which are, you know, yet smaller and simpler organisms, can muck it up, can produce different fermentations that, that lead to results we don't want. That was, you know, another big step. But the, you know, I think this is where one of the theme, you know, this is where I argue something that I think is, is, I hope, one of the You know, one of the bits in the book that people engage with, I mean, they feel free to disagree, but, but, you know, asking the question, why did it take so long?

• 1:06:34Speaker 03

  You are ultimately asking for, you know, cultural and social reasons. And the, you know, a gentleman's hands are clean is one example of essentially hierarchical thinking. There is a social order and people at the top of the order are not capable of and certainly not responsible for bad things happening lower down. Well, there's a broader sense of that, and I think it starts in religion, but certainly doesn't just stay there. This notion, you know, the, the, yeah, scali naturi in Latin, scale of nature, and often referred to as the great chain of being, which was the title of one of the classic books in cultural history, Lovejoy's The Great Chain of Being.

• 1:07:17Speaker 03

  But, you know, it's this notion, and you see it in the first chapter of Genesis, that, you know, there is God, there are heavenly creatures, and then there's humankind. And all the rest of creation is given into our dominion explicitly in the text of the, you know, that first chapter of Genesis. And this gets elaborated in a bunch of different ways, and you get, you know, by the Middle Ages and later, you get these, you know, beautiful elaborate drawings showing, you know, an old white haired gentleman, gentleman sitting on a throne at the top and angels with their wings and then people and then all the way down to rocks and dirt, you know, through all, through the ranges, you know, some hierarchically organized view of the

• 1:07:59Speaker 03

  kingdom of life and so forth. And one of the things that that structure, I think, makes it easy to believe and hard to disbelieve is that authority goes from the top down and not the way, authority and agency and not the other way. Right.

• 1:08:23Speaker 03

  I think, and again, you see those ideas, it doesn't have to be divine, you know, or the divinity and the explicitly religious framing of it can drift very far into the background. The idea that, you know, humankind is superior to the animals is one that you can believe without needing to have, you know, the authority of Genesis. The idea of white people are entitled to rule others is certainly one that was persuasive to an awful lot of people for a long, long time, and perhaps to some folks still. You know, the idea that there is a hierarchy of agency and authority is one that persists

• 1:09:06Speaker 03

  in lots of different domains. And I think it mattered here. I think it was very, very hard to imagine that microbes, which were delightful to look at, and it's wonderful to be a tourist in the microcosmos, the idea that they could turn around and have, you know, agency or impact on, you know, us, crowns of creation, it's a very hard thought to think. You need, I think, and that's one of the things I think I chronicled in the book, you need to accumulate a lot of, you know, ideas and specific instances where

• 1:09:47Speaker 03

  you see something is going on in the disease process that needs explanation, to really kind of let go of the idea that, that, in some sense, the bad things that happen to humans, humans do to each other.

• 1:10:05Sean Carroll?

  Yeah.

• 1:10:06Speaker 03

  That's an easy idea to master, but to extend that and say, well, you know, despite our big brains and our opposable thumbs and our tool-using, these, you know, single-celled simple creatures can really mess us up, that takes some thinking.

• 1:10:23Sean Carroll?

  Okay, and do we properly give Pasteur credit for finally saying that out loud, clearly, for everyone to see? I know there was some controversy.

• 1:10:35Speaker 03

  I mean, yes, I think Pasteur and Robert Koch are the two people who are who are most associated as the the the major founding figures in germ theory. And yes, they did, they were enormously. You know, they had enormous impact, they made major discoveries. They were rivals. Pasteur really did try to undermine Koch's sort of claim of unique discovery with with the anthrax bacterium. Probably, you know, he Pasteur did important stuff with anthrax, including coming up with an anthrax vaccine.

• 1:11:17Speaker 03

  But but he certainly over overstated and, you know, he did he he did mess with Koch. Koch did not take that well and responded, you know, really in in very hostile and even more belittling terms to Pasteur. Most of that just doesn't matter. I mean, it didn't matter at the time. Both people, you know, went on and had had the careers they had without really impediment. It just clearly pissed them both off. And there was an enormous, at that point, I also remember there's an enormous Franco-German rivalry. Exactly. Germany stomped France in the in the War of 1870. So there was that nationalistic animus as well.

• 1:12:01Speaker 03

  But again, it's important to realize that that I think, you know, one of the Pasteur seeded some of the first major, you know, derivatives of germ theory. News of his work on yeast and fermentation reached Joseph Lister, a doctor practicing in Scotland. And Lister realized that if these bacteria lurking in in the air could contaminate beet juice or beer or what have you, then they could also perhaps explain the terrible problem

• 1:12:41Speaker 03

  of surgical wound site infections, which were basically made, you know, much surgery impossible to do and many surgeries very dangerous. And, you know, you would have a compound fracture of a limb and more often than not, surgeons would amputate rather than treat because the likelihood of infection was so high, that kind of thing. And Lister invented essentially sterile surgery and showed that you could, in fact, if you did, you know, originally very elaborate work to try and, you know, wall off the wound site from bacteria, you could, in fact, perform surgeries that had, you know, previously been fraught with danger or simply unthinkable.

• 1:13:25Sean Carroll?

  I do wanna, go ahead.

• 1:13:26Speaker 03

  I'm sorry, go ahead. I was just saying, that happened in the 1860s.

• 1:13:30Sean Carroll?

  Yeah.

• 1:13:30Speaker 03

  Tragically, it happened just after the Civil War. So you have this.

• 1:13:34Sean Carroll?

  Civil War was tough.

• 1:13:36Speaker 03

  Yeah. And, and, you know.

• 1:13:38Sean Carroll?

  If you got hurt.

• 1:13:39Speaker 03

  Yeah, more people died of disease and wound infections than died of, you know, immediate battlefield trauma.

• 1:13:48Sean Carroll?

  Right.

• 1:13:48Speaker 03

  By like two to one.

• 1:13:50Sean Carroll?

  Well, the chronology is definitely interesting, so I wanted to, you know, again, skip to the highlights here, but vaccination, now real vaccination becomes a real thing, but it did predate, again, Pasteur, but he, he had a famous experiment with the sheep that I really loved, even though, I mean, it's famous in some circles, but let's pretend that not everyone listening has heard about it.

• 1:14:12Speaker 03

  Okay, so, as I said, Pasteur invented an anthrax vaccine.

• 1:14:18Speaker 03

  Again, there had, one of the reasons why it's always fraught to say, well, Pasteur was this great giant colossus of stride, yes or with, people had identified a bacterium with anthrax cases before that. These, you know, these rod shaped bacteria were showing up.

• 1:14:39Speaker 03

  And, you know, people actually explicitly wondered if they were simply a correlate, you know, you get sick with anthrax and that makes your body, your body less, you know, able to defend itself against, you know, the slings and arrows of outrageous fortune, and these bacteria are opportunistically, you know, making their home in your bloodstream, that kind of thing.

• 1:14:59Speaker 03

  Nobody actually sort of definitively established that these bacteria were the pathogen until Koch did it.

• 1:15:06Speaker 03

  But there was, you know, there was this, you know, it was certainly known that this bacterium was present in essentially all cases of anthrax by, you know, a decade or more before Pasteur started working, two or three decades before Koch got, got his, got his interest going.

• 1:15:25Speaker 03

  So.

• 1:15:27Speaker 03

  Coke identifies and establishes and nobody, you know, it's, it's, it's now, you know, clearly the correct answer that this one particular bacterium is in fact the source of the symptoms of the disease when they infect an animal or a person. And Pasteur works to, his basic method was to try and, you know, pass the bacteria through repeated animals until it was attenuated. Keep, you know, recycling it. And, you know, he tried different, aging them in cultures. And there are lots of different ways that he worked to try and create less pathogenic

• 1:16:10Speaker 03

  versions of, of the microbe. And he eventually got it. Again, there's a little controversy. Did he in fact have a live attenuated vaccine by the time he did this famous experiment? Or had somebody worked on actually a killed version where they actually fixed the bacteria in some chemical? There's, you know, the notebooks are a little funky there. But, and he announced that he had a vaccine and some anti-germ theory, an anti-germ theory doctor said, prove it. And challenged him to this test where he was gonna take, there would be two groups

• 1:16:53Speaker 03

  of sheep and there were, I think there were a couple of goats involved as well. And they're gonna separate them up and half of them, all of them were gonna get injected with anthrax. So, you know, given the disease and then half would be, but half would have been previously injected with the vaccine and half would not. And Pasteur said, okay, and took his vaccine to this, to this, you know, farm not that far out of Paris and did the test.

• 1:17:27Speaker 03

  And it was one of those, you know, like they draw it up kind of experiences where basically all the control group that went unvaccinated died and all the vaccinated animals were, you know, happily gambling around the fields. And it was regarded and presented certainly in the popular press, which Pasteur was really good at representing himself in as this sort of clear triumph and clear demonstration of the truth of germ theory.

• 1:17:54Sean Carroll?

  You know, it's, it's one of the things we didn't, you, you wrote a long book. I'm sorry, Tom, but we didn't get to talk about all the cool stuff. People should buy the book. But one of the themes that comes through, aside from the sort of establishments always resisting you is the effectiveness of good science communication and in particular graphic design, you know, Florence Nightingale, Jon Snow, and certainly Pasteur was a, was a master of publicity. They, they, they got their points across, not always by just having the better data or theory, but by being, you know, a little, there's, there's some showmanship involved as well.

• 1:18:31Speaker 03

  Absolutely. I mean, and, and, you know, that's no surprise.

• 1:18:36Sean Carroll?

  No surprise at all, even when you say it that way. Yeah.

• 1:18:39Speaker 03

  I mean, it's just, I mean, I guess what's surprising to us with our present, presentist bias is that they figured that out, you know, back then. But, you know, again, Robert Hooke, you know, that book Micrographia, he, you know, he, he wanted, he wrote that book to sell and it did. But yes, it is interesting to me that, as you say, Nightingale with her, essentially the invention of polar diagrams. Nightingale was a formidably intelligent and gifted person. She had, she had an unusual education for aristocratic young women or, you know, elite women of her time. She did have some training in mathematics and she

• 1:19:23Speaker 03

  really had a gift for data representation that, you know, Tufti would have been proud of, I think.

• 1:19:30Sean Carroll?

  You know, you don't think Florence Nightingale, graphic designer, but very much that was in her wheelhouse.

• 1:19:36Speaker 03

  And she was able to, you know, these, these lovely circular, she called them Cox comb because they were supposed to supposedly vaguely like that, you know, thing on top of a rooster's head. But you know, you could really see the change in death rates from before and after introducing, you know, proper hospital hygiene in the Crimea, Crimean war. And similarly, John Snow's sort of gift for graphical representation, you know, map, map-based, geographical, I'm sorry, not graphical, geographical representation of data, again, made his case that small, not smallpox, cholera was a disease of some specific contaminant in water.

• 1:20:20Speaker 03

  I mean, very, very difficult to argue with. I mean, people did, but still, it was a very persuasive case.

• 1:20:27Sean Carroll?

  Yeah, just so people know, like, these are maps of, you know, block by block, house by house in London. These people got it, these people didn't. Here's the water supply. Draw your own conclusions.

• 1:20:37Speaker 03

  Right. It was, you know, it was even, you know, it even sort of accommodated the fact that London's streets are this ridiculous tangle.

• 1:20:47Sean Carroll?

  Exactly.

• 1:20:48Speaker 03

  Because, you know, Snow was able to show that even though some of the cases of cholera that were centered on this one bad, you know, source of water, the Broad Street pump, that some of those seemed to be, you know, quite far away, and there were other, you know, houses nearer that weren't affected. But he was able to show that, that even though the crows, you know, the crows flight, birds' flight distance was greater to those places, the actual distance through the streets to the water supply.

• 1:21:19Sean Carroll?

  Right.

• 1:21:20Speaker 03

  All the cases were in houses where the closest water supply was that one pump on this, you know, street in Soho. I mean, he was, he was good.

• 1:21:32Sean Carroll?

  And despite all of this human genius, we can wind it up by coming to the present day. Not everyone is convinced. I mean, maybe before explaining that not everyone, even in the present day, is convinced of not just the efficacy of vaccines, but even, I hesitate to say it, but some people are a little skeptical of the germ theory of disease right now. But let's just remind ourselves how effective vaccines have been in making the world a better place. I mean, you paint a vivid picture, not just, you say you cure disease, that sounds good, but a wholesale change in life expectancy and demographics more generally that we kind of take for granted now.

• 1:22:16Speaker 03

  Yeah, I mean, the, the one message I'd like to leave with anyone listening to this is our release from the fear of infectious disease is, in historical terms, incredibly recent. You know, people are familiar with the story of, of, of, you know, public health infrastructure. You, you know, you create clean water, you create, you know, you, you get clean air, you reduce the incidences of all kinds of diseases enormously. If you just did that, it would be a huge change. But the combination of vaccines and antibiotics means that for at least people in the developed

• 1:22:57Speaker 03

  world, and increasingly in, in, in, in the rest of the world, diseases that were once inescapable are now, you know, preventable or curable really readily. And, you know, in London, you know, as late as 1900, there was still a significant rate of infant and child mortality. And that basically is not a problem. Yeah. The fact that the US child mortality, infant mortality is worse than the rest of the developing world is a fact and a serious problem, and has social and, and political roots, not medical ones.

• 1:23:40Speaker 03

  We know we can prevent these, these maternal and child deaths. And the fact that we don't is in fact a, a social choice, even if we're not conscious of making it. But broadly speaking, you know, in 1952, there was a terrible polio outbreak in the United States, and thousands died and more were affected with, you know, lifelong consequences. And two or three years later, the first polio vaccine came out, and that threat, you know, our parents or our grandparents were terrified to let their kids go to the swimming pool in the summertime in the 40s and 50s. You know, that's no longer an issue. Yeah.

• 1:24:23Speaker 03

  The vaccines against common childhood illnesses. There were a few coupled done before the war, before the Second World War. But most of them emerged between 1950 and the end of the 1960s. That's not very long ago. It's recent enough so that I am, though I'm sure you wouldn't think to look at me, old enough so that I was a kid before the Rubella vaccine, which was the last in the list to show up, was available and I caught a case. German measles, it was also called. Yeah. And it was really unpleasant. And I was lucky because there are possible lifelong consequences for Rubella. And I didn't get them, so that's great.

• 1:25:08Speaker 03

  But, you know, this is living memory. And now, however, or up until very recently, those things were, I mean measles was declared eradicated in the US around 2000. It's back.

• 1:25:26Speaker 03

  The, you know, up until very recently, no one, no parent had to, had to seriously worry that their child would be killed or damaged by diseases that for almost all of human history were devastating companions, just things that you had to deal, live with. So, and again, I think there, there are a lot of different reasons for this. There are explicit political reasons. There are, you know, just the fact that amnesia, you know, the sort of this, this lack of experience means it's very hard to credit that the threat exists. That's a, a human, you know, perfectly normal human reaction to things.

• 1:26:11Speaker 03

  If, if you've never seen it, it's hard to believe it's real, right? But the anti-vaccine movement and more broadly, the sense that public health in general, not just vaccine regulations, but the other things we might do, like, you know, wear masks and, and physically separate during COVID. These are, are seen by I think too many as unwarranted intrusions into the individual liberties of, you know, of, of everyone.

• 1:26:47Speaker 03

  And that's not precisely the same as the kind of hierarchical, you know, chain of being kind of stuff I associate with with the difficulty of getting to germ theory. But it's clearly a kissing cousin. You know, there is a sense that there is a, you know, still a hierarchy of agency.

• 1:27:07Sean Carroll?

  Hmm.

• 1:27:08Speaker 03

  My choice is inviolate.

• 1:27:11Sean Carroll?

  Right.

• 1:27:12Speaker 03

  And, you know, other, you know, it's a. And you see that, you know, you see that happening in our politics right now. RFK Junior is, is, um, his HHS is rewriting vaccine guidelines to emphasize that vaccines are an individual choice and that there are complications and all that sort of stuff. There are risks to vaccines, et cetera, et cetera. And this is very much locating the, um, the choice and decision making power over the, you know, sort of creation of these ecological niches for, for infectious disease.

• 1:27:52Speaker 03

  It's locating that in, in, um, you know, your choice and my choice and everybody else's choice. And, um, you know, if the consequences of those choices were confined to the individual, that would be one thing. But one of the things about infectious disease is it is, wait for it, infectious. It moves from person to person. So those choices have impacts beyond the individual. And that's something that we find in our society right now and in our politics right now. Something that's very, very difficult to accommodate.

• 1:28:29Sean Carroll?

  And it's also a case where, you know, you can believe whatever you want, but at some point, as a scientist, I do believe there are objective facts out there about how the world operates. But there are crucial differences in the time scales and tangibility of those facts. You can think you can walk through a door, but if you try it, you will instantly figure out you don't. You can think that vaccines, um, cause more harm than good and you can get away with it. It for a while, right? You know, for months, years, whatever other people are being affected. I'm not being affected. And so it's just so much harder to, you know, overcome all of the human foibles in the equation when there's there's that much wiggle room

• 1:29:14Sean Carroll?

  in something, a complex system like society, politics, medicine.

• 1:29:19Speaker 03

  Absolutely. And, you know, I should emphasize, you know, the one of the things that's happened, you know, there was vaccine hesitancy from the very beginning. And in earlier times, there was generally more reason behind it. There was, you know, vaccine like any other technology has has advanced and improved over time.

• 1:29:41Speaker 03

  But, you know, one thing that's really different in 2025 than was true in 1970 or 1920 or 1850 is, you know, an understanding of

• 1:29:58Speaker 03

  sort of disease and immunity down to the molecule, you know, molecule or atomic level, right?

• 1:30:06Speaker 03

  These are extremely well characterized. You know, it's not that you know, everything. There's lots and lots of stuff that is not known about specific mechanisms and pathways and all kinds of stuff. But an enormous amount is known and the the mechanism by which vaccines have their impact. The reasons why some vaccines are like confer lifelong or or extremely long lasting protection and others do not is part of the, you know, interaction between vaccine and pathogen. All these kinds of things, these are understood. They've been well characterized and and there's, you know, there's no room for doubt anymore about the fact that A vaccines work, B, how they work, and C, what their limitations are.

• 1:30:52Speaker 03

  And D, what the consequences of rejecting all that can be, it can be, you know, one of the things that happens is, is, is, you know, if polio were to escape, I've seen, I've seen model studies that show that it could very, very rapidly produce extremely large scale outbreaks because the, you know, the, the global, the global state of, of polio vaccination has been waning since polio has been eradicated.

• 1:31:18Sean Carroll?

  Why do you need to vaccinate?

• 1:31:19Speaker 03

  Yeah. Well, you know, it's, it's, it's, it's gone everywhere in Afghanistan or Pakistan. And the only reason you'd vaccinate now is if a, is if a, you know, a case showed up.

• 1:31:28Sean Carroll?

  Yeah.

• 1:31:29Speaker 03

  Yeah. So the, you know,

• 1:31:35Speaker 03

  the risks are real and growing. And one of the things you'll see is, as, as I suggested earlier in the book, that some of the issues in thinking about microbes were unrelated to anything to do with the science of microbes or the natural history of microbes at that time. But to, you know, well established social and cultural predispositions. Well, similarly, right now, a lot of the anti vaccine stuff is now has sort of leapt the bounds of, say, the autism community where they were terribly misled by that, you know, early paper that suggested falsely that there was a connection between autism, vaccines and autism.

• 1:32:16Speaker 03

  Now it's left the bounds, but I think for an awful lot of people, being anti vaccine is not actually a statement about what you know or believe about how the immune system works. It's a, it's a, an affinity marker of I'm with this group and this group has included as part of its, you know, political catechism that vaccines are, are, are a, are a bad thing.

• 1:32:41Sean Carroll?

  Yeah, we just talked about that literally with, recently with a political scientist, Liliana Mason. And I mean, you and I both know that 10 years ago, if you said, it's so annoying that conservatives are denying science like climate change or whatever, you would get the response, but you know, the liberals deny vaccines or, or modern medicine and so forth. And it's, it's shifted quite a bit for obvious reasons.

• 1:33:06Speaker 03

  It has, and you know, I mean, and again, it's not surprising. You know, all of us offload some of our knowledge and judgments to, you know, We don't have time to become masters of many things, much less everything, right? So if people we admire and respect say, you know, the sun rises in the east, we don't actually need to go out there with a compass and make sure of it ourselves. And that's true for all kinds of things. So when, you know, too many political leaders, you know, make, make political hay out of, you know, opposing vaccines or what have you. It's not surprising that large sections of their, you know, of their followers would

• 1:33:51Speaker 03

  say, okay, well, that, you know, I don't need to go study that myself. You know, Joe Rogan or whoever says this and, and, you know, he wouldn't lie to me on the radio, whatever. Robert F Kennedy says that, you know, he's the Secretary of Health, you know, Health and Human Services. He's not going to lie to me, et cetera, et cetera. And you just go on about your business. And again, it's not surprising. It's very human. We all do some variation of that, but in this case, it has tragic and fatal consequences.

• 1:34:17Sean Carroll?

  So don't take it personally, Tom, but after the podcast is over, I'm going to go wash my hands. You put the cleverness into our heads. But Tom Levenson, thanks very much for being on the Mindscape Podcast.

• 1:34:29Speaker 03

  Thank you so much for having me, Sean.

• 1:34:55Speaker 00

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