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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