Microbes and Man 2014


On June 28th, 2014, in room 202 of the Salem State University library, between 11 and 2 o’clock, a seminar took place entitled Microbes and Man: Mankind’s Invasion of the Planet of the Microbe. I had organized the conference to meet several objectives, including a desire to explore my developing interest in the history of science, disease, and medicine; to offer a historical perspective on subject matter of interest to students outside the history department; and to exchange ideas with students with similar interests. The seminar itself, as well as the experience of organizing it, proved extremely rewarding, and I am likely to repeat the seminar in the future. The following are my reflections on the material and is informed in part by the discussion that took place at the seminar. 

Transforming Earth’s Biomass

The seminar left me feeling that the widespread attitude that human beings simply destroy ecosystems, as if we are rendering the planet less verdant, is myopic. Human beings do not simply destroy biomass; they transform it.

Human civilization has been a destructive force for many species, but it has been a constructive force for many others. Human actions turned aurochs into cows, whose numbers today dwarf any conceivable estimate of the numbers of ancient aurochs. Human actions turned wolves into dogs, and human actions branched those dogs into countless breeds. This constitutes a form of biodiversity, and it was a consequence of domestication, for many of these breeds are, while adorable, physically meek and would not survive in the wild. Similarly, human civilization is the natural habitat of many a rat species.

In other words, human civilization has reduced the proportion of the earth’s biomass that exists in the form of many species (the dodo, for instance). But it has dramatically expanded the proportion of the biomass that exists in the form of dogs, cats, rats, sheep, pigs, cows, horses, etc.

This transformation from one type of biomass to another is an ordinary event in the history of life. The earth is a churning, ever-changing planet, and so its biomass (that portion of its matter that is organized into what we call life) changes. What Lynn Margulis and Dorion Sagan have called the “oxygen holocaust” of between 2 and 3 billion years ago killed many a prokaryotic species but made possible eukaryotic species (including us). Sixty-seven million years ago an asteroid struck the earth, wiping out a substantial portion of the earth’s biomass—the dinosaurs—but thereby opening up new niches for others kinds of life, such as the primates from which human beings descend.

The destruction of one environment and its species has always meant the creation of a new environment and the expansion of new species. Human civilization has razed some environments, but it did not replace them with nothing. It is ghastly to contemplate the destruction of a rainforest, with its unfathomable complexity, biodiversity, and beauty. After this seminar, however, acknowledging only the destructive dimensions of human actions seems unsatisfying. The relationship of the cattle that likely replaced that rainforest to the species that preceded them is something like the relationship of human beings to the prokaryotes of the “oxygen holocaust” or the dinosaurs wiped out by the asteroid. Whether it is eukaryotes thriving in an oxygen rich atmosphere, mammals radiating onto land, or cattle grazing on razed rainforest, life adapts to the environments available, and the graveyard of one species is the cradle of another.

This is as true for plants and insects as it is for (non-insect) animals. Domesticated maize, for instance, is a form of life whose abundance is a consequence of, and whose survival is entirely dependent upon (it could not survive in the wild), human civilization. Similarly, human population growth has provided mosquitoes (the most dangerous animal in the world according to Hadyn Parry (insects are, of course, animals)), with an inexhaustible reservoir of human blood.

Microbes. Organisms too small for our eyes to perceive them individually. The first lifeforms were microscopic, and it is from this microscopic universe that all life descends. As a proportion of the weight of the earth’s biomass, bacteria are the earth’s dominant lifeform.

What has been our impact on the microbial life of the planet? No doubt many a microbial lifeform has run to extinction as human activity has transformed ecosystems. Every extinct animal probably took with them microbial lifeforms unique to their species. Just a handful of rainforest soil contains countless unrecorded forms of microbial life.

Nonetheless, human civilization catalyzed a microbial demographic explosion perhaps without parallel in the history of life on land. This is because no species has combined population densities, rapid global migrations, and rapid revolutionary (and reckless) cultural transformation to the extent that human beings have. Looking at it on an evolutionary timescale, the movement of life from one continent to another aboard ships or airplanes amounts to teleportation, taking place in an evolutionary instant. Combining the human ability to culturally adapt rapidly (quickly adopting lifestyles in which we live in close proximity to animals, close proximity to human and animal excrement, and the ability to traverse the globe), with the microbial ability to genetically adapt rapidly unleashed a flood of new species of bacteria and viruses across the planet, altering the microscopic biome of the entire planet in just a few thousand years.

Our own demographic explosions in themselves have expanded the earth’s microbiome, for we are walking microbial ecosystems. For every large human cell in our body (approximately 10 trillion) there are 10 tiny microbial cells (100 trillion). When agriculture removed the Malthusian breaks on human population growth, and when the Industrial Revolution accelerated this development, the increase in the number of human bodies on the planet meant the addition of countless acres of prime microbial real estate in the form of human digestive tracts, epidermises, etc.

There are seven billion people on the planet today. 7 billion times 100 trillion is 10-to-the-22nd-power. That’s an approximation of the quantity of individual bacteria that our bodies contribute to the earth’s biomass, and they ought to figure into any assessment of the impact of humanity on that biomass.

Invasions, extinctions, dramatic events (imbalance) are all routine dimensions of the history of life on earth. Our species represents one of a galaxy of factors in a fleeting phase in that history. None of those factors, anthropocentric or not, are best understood as purely destructive. Life adapts. And microbial life, which has always been the dominant form of life on the earth, is the most adaptable. Cattle, maize, and cholera are all legitimate forms of life for which human civilization—assessed exclusively from the standpoint of their proportion of the earth’s biomass—has been nothing but a boon. For many species, human civilization was the Big Bang of their universe.

Of course, this isn’t to say that the reduction of biodiversity outside of human civilization should be shrugged at. If we had to choose between shrugging our shoulders or adopting a the-world-would-be-better-off-without-people perspective, the latter has plenty of strengths to recommend it. Indeed, the reduction of biodiversity within civilization, in the form of growing massive quantities of identical species of grains, for instance, is a major concern in itself. However, after Microbes and Man, my perspective on these issues is more nuanced, and I feel less prejudiced against the broad array of lifeforms—many of which are harmful to us—that the growth of human populations has fostered.

Not destruction. Transformation.

Models, Not Truths

A simple model of how science works is provided by the following: scientists formulate a hypothesis and test it. They make observations, formulate a new hypothesis, and test it. Etc.

That’s really basic. There is an unspoken assumption that I think many people hold, however. The assumption is that eventually scientists reach the truth. If they didn’t, wouldn’t all that experimentation be pointless?

I appreciated that many of the authors I have encountered in reading about the history of disease and medicine have implicitly recognized the fallacy of that assumption. People once believed, for instance, that disease was caused by chemically poisonous air, what they called miasmas. Guided by these beliefs, London began creating sewer systems in the nineteenth century. No longer would excrement be allowed to accumulate in cesspools below houses, creating toxic air, but it would be pumped into the Thames to be washed away. In other words, people thought that the air was poisonous because it smelled bad, and in response they pumped raw sewage into their drinking water supply, where at least they couldn’t smell it.

Aside from being in poor taste (oops, that’s a pun) to ridicule people who were suffering greatly, ridiculing their beliefs would imply that we are not obliviously engaged in similarly self-destructive behavior. Of course, we consciously engage in many self-destructive behaviors—greenhouse gas emissions, cigarette smoking, etc. So I was glad that our authors (I am thinking of Steven Johnson in particular), while being entertaining, didn’t fall into the foolish paradigm of contrasting our ignorant predecessors to our knowledgeable selves.

But more important than the fact that we know we are engaged in self-destructive behavior is that we are likely engaged in self-destructive behaviors that we do not yet recognize are self-destructive. Put more simply, it is foolish to imagine that we know the truth, while they were ignorant of it.

Most nineteenth-century Londoners did not subscribe to germ theory, a theory that competed with miasma theory in trying to explain disease. Of course, disease can be caused by lots of things, including chemically poisonous air, i.e. miasmas, but the most significant diseases until very recently in human history were all infectious diseases, i.e. those caused by microscopic organisms. The cholera with which Londoners were suffering is one such disease.

Microscopic organisms were first seen by human eyes in the seventeenth century by Dutchman Antoni van Leeuwenhoek. He saw tiny organisms in his saliva and concluded that they were benign. In the middle of the nineteenth century Louis Pasteur demonstrated that microscopic organisms were responsible for fermentation. Pasteur was a contagionists (someone who believed in germ theory). He created vaccines for rabies and anthrax. However, Pasteur was explicit: while some germs cause disease, many do not, and others may be beneficial to human beings.

Such nuanced views of microbes receded and were all but forgotten as germ theory won converts and what Sachs calls humankind’s One Hundred Years War on Germs got underway. Vaccines were developed to provide protection against viruses that had ravaged humanity for millennia, such as measles and smallpox. Antitoxins were developed that neutralized viruses such as diphtheria and tetanus. In the first decades of the nineteenth century, sulfa drugs were developed, able to cure and prevent bacterial infections. In the 1940s and 50s antibiotics such as penicillin transformed medicine. Before sulfa drugs and antibiotics, doctors could offer almost exclusively prevention. Once you contracted an illness, you were as helpless in 1900 AD as you had been in 1900 BC.

The crude idea that germs are bad got us pretty far. But what we concluded with in the seminar were some readings on the unintended consequences of this war on germs, consequences which demonstrated the shortcomings of germ theory in the form it had taken once shorn of the nuances with which folks like Pasteur had adorned it.

If the 100 trillion microbes that inhabit the human body (2-5% of our body weight) were removed, we would not be able to digest many plant substances and our immune systems would be rendered feeble. In other words, we evolved in concert with our microbes, and just as we provide them with an ecosystem, so they provide beneficial functions for us, without which we could barely survive, if at all.

Guided by a crude version of germ theory, since the 1940s we have been effectively carpet bombing our microbiome. Scientists are beginning to link our germ-free lifestyles with autoimmune disorders, such as asthma. Some, such as Martin Blaser, are convinced that obesity can be linked, at least in part, to the destruction of microbes whose products play a role in regulating human appetite.

The use of antibiotics has also bred resistance to those antibiotics. In any population of bacteria, some may be resistant to a particular antibiotic. When we use antibiotics, we kill those that aren’t resistant, allowing those that are resistant to grow. Indeed, tens of thousands of Americans die each year after becoming infected by antibiotic-resistant bacteria. With continued use, those numbers will grow, until one day, we will have finally reverted to the status quo ante, in which, once our invisible nemeses penetrated our defenses, they exploited our bodies with impunity, impervious to our desires, our death or survival the incidental, unconsidered consequences of their own life processes.

In other words, germ theory was wrong. Of course, it was right about some things, but so was miasma. Again, some diseases are caused by exposure to poisonous chemicals. And removing the cause of bad odors frequently does reduce exposure to the microbes that cause infectious disease. If Londoners hadn’t pumped their sewage into their drinking water, if they had pumped the foul smelling material elsewhere, the miasmaist solution of removing foul smelling material would have worked (as it did once they pumped the sewage elsewhere).

What does science offer, then? A scientific model is a model used to make predictions. The classic example of one modeling giving way to another is that of the Ptolemaic geocentric universe (the Sun revolves around the Earth) giving way to the Copernican heliocentric universe (the Earth revolves around the Sun). The difference between these two models is not that one is “right” and the other “wrong.”

The difference is that the Copernican model yields more accurate predictions. Accumulated astronomical observations had rendered it necessary to add qualification after qualification to the Ptolemaic model; those same observations were all predicted by the Copernican model.

When it comes to miasmaists and contagionists, germ theory won converts because it provided more accurate predictions than miasma. Miasma would not have predicted the following: that specific microbes could be found in the bodies of those who died of specific illnesses, and that when those microbes were injected into lab animals, the animals developed that particular illness. This is a very simply version of Koch’s Postulates, a set of criterion laid out by Koch as a means of testing germ theory. In the late nineteenth century, germ theorists began meeting these criteria for a number of diseases, providing powerful verification of the theory.

Germ theory prevailed, but we are now finding that we need a new model. As alluded to, Leeuwenhoek and Pasteur already provided us with the insights we need, we just collectively ignored them in practice: some germs are bad, but others are good, and many are beneficial. What is emerging, and will perhaps inform the medicine of the twentieth-first century, is a more ecological view of our microbiome. “Probiotic” yogurt can now be found in the refrigerators of people whose parents would likely have scarce dreamed that promoting germ growth would facilitate good health. (The jury is still out on the benefits of such yogurt.)

What I wonder about is: What model will follow this ecological view? Are there any obvious blind spots in germ theory and our more ecological version of germ theory? My guess—purely a guess—is something like a “selfish gene” version. I can imagine us coming to emphasize that our microbes are themselves a constellation of genetic material, and instead of thinking of one germ as good and another as bad, we may come to view particular genes (or sets of genes) as good and others as bad. Rather than seeking to destroy the harmful microbe, perhaps we will seek to genetically alter it. The genetic manipulation of insects to reduce the spread of disease is already taking place, as discussed by Hadyn Parry in the TED Talk we viewed for the seminar.

War and Disease

War facilitates the spread of disease in some obvious ways. Wounds open up the human body, leaving it vulnerable to invasion by unwelcome microbes. The movement of soldiers into a foreign country means the movement of their microbes, some of which the enemy soldiers and civilians likely do not have resistance to. Soldiers typically live in unsanitary conditions and do not have resistance to the microbes of the place they are invading. War also breaks down societal institutions that govern sanitation and medicine.

Some of the interactions between war and disease surprised me though. War congregates people well before soldiers reach the battlefield. When the United States mobilized for war, soldiers of variegated backgrounds came into contact with each other, and each other’s microbes, for the first time. Mobilizations took many people from rural settings, where they interacted with domesticated animals, and brought them into urban settings for the first time. Before the country’s soldiers had set sail to confront their human enemies, influenza and measles had already invaded American barracks. Influenza would infect perhaps half the world’s more than 1.5 billion people between 1918 and 1920. Estimates of the death toll range from 20 million to 100 million, or perhaps 5% of the world population.

But it gets more complicated. In Philadelphia, the largest shipyard in the world was established, drawing in a mass of workers. War, in other words, congregates people for the purposes of industry. In the nearby naval yard, the infectious microbes of the sailors seeped into the civilian population. When Philadelphia congregated people for the purposes of raising money (Liberty Loans) and morale (a giant parade), it facilitated the spread of those microbes.

It gets more complicated, and we still haven’t reached the battlefield. The diseases wrought by mobilization (soldiers into barracks, workers into factories, civilians into the streets for parades) impeded mobilization. Soldiers died before leaving the country, or were temporarily incapacitated. Workers stayed home from work, either to convalesce or to avoid contracting influenza. Doctors needed abroad were excused from serving because their services were now needed domestically.

War also plays a counter-intuitive role in the history of medicine. Disease has frequently felled more soldiers in war than then enemy swords or bullets, and so efforts to control disease have frequently accompanied warfare. War brought Florence Nightingale to the Crimea, and it inspired the founding of the Red Cross. It was in response to the influenza pandemics of the 1920s, facilitated by the First World War, that the National Institutes of Health were established in the United States. And it was following World War Two that the World Health Organization established the international influenza monitoring system that we use today.

Disease and Veterinary Medicine

Something that stood out in the readings is the relationship between human diseases and domesticated and wild animals. The most obvious dimensions of this relationship are that human diseases originate in (or on) animals: rabies from dogs; influenza from birds and pigs (NPR recently had a story about influenza leaping to people from camels); plague from microbes living in the fleas living on rats.

An interesting aspect of this relationship is the significance the animal origins of diseases has for human control of microbes. Zoonoses (a zoonosis is an animal disease that humans can contract) cannot be eradicated. Smallpox is an example of a disease that is not a zoonosis. It is caused by a virus that only infects human beings. If you vaccinate enough people so that the virus has no one to infect, it will go extinct. Indeed, such a project was embarked upon in second half of the twentieth century, and in 1980 the WHO declared smallpox eradicated from the natural world. (The United States and Russia retain the smallpox virus in laboratories.) Polio has come close to extinction because it too only infects human beings.

Most infectious diseases, however, continue to exist in animal populations, periodically leaping into human populations. Influenza is one such zoonosis. No matter how well you vaccinate a population against influenza, soon thereafter a new strain, for which the previous vaccine is useless, will leap into humans from animal populations.

Finally, veterinary medicine made a brief but important appearance in the seminar. The experiments that proved the effectiveness of Louis Pasteur’s vaccine for anthrax were an important event in the history of germ theory, and that vaccine was for livestock, not people. We did not have an opportunity to explore this issue, but our One Hundred Years War on Microbes has been directed not only at microbes that infect people, but also those microbes that infect domesticated animals. At least until recently (and perhaps still), the vast majority of antibiotics humans used were not used on people but on livestock. This is because animals fed a steady diet of antibiotics grow larger quicker. The European Union banned the use of antibiotics as growth promoters in 1999, and I believe this issued was recently addressed by Congress, but we didn’t have an opportunity to look at it during the seminar.

Conclusion

Microbes and Man: Mankind’s Invasion of the Planet of the Microbe was an incredibly intellectually stimulating experience. I hope to hold future permutations of the seminar, and I envision one day presenting it as a credit course at a university.


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