When it comes to the world of the micro, there’s
a little bit of something for everyone. Do you feel a kinship with chill blobs that
contain hidden depths? Well, there’s plenty of amoeba to understand. Do you love complex choreography? Well, then you might want to catch a performance
by bacillaria. And if those don’t draw you in, there are
hunters, living jewels, and complicated lifestyles aplenty to explore. For microbiologist Dr. Lynn Margulis, the
draw was symbiosis. The microcosmos is made of many, many organisms
who don’t just occupy the same space, they collaborate. Whether it’s for protection, nutrition,
or just some help getting around, these interactions may seem small, but their implications are
enormous for all life on earth. Through the second half of the 20th century,
Margulis’ dedication to understanding symbiosis transformed our understanding not only of
microbes, but of ourselves. Her legacy is a complicated one, rooted in
a stubbornness that at times paid off in major scientific understanding, but also made her
unwilling to acknowledge the limitations of her work. At the core of her efforts though is a dedication
to microbes and to understanding what they can teach us about the world. Lynn Margulis published many books and articles
about microbes for both academic and general audiences. But perhaps her most impactful work was also
one of her earliest, an article published in 1967, shortly after she began working at
Boston University. The paper was titled “On the Origin of Mitosing
Cells,” and over its roughly 50 pages, Margulis argued that some of the organelles inside
eukaryotes were actually once—long, long ago—free-living prokaryotic organisms. What she was describing was the theory of
endosymbiosis, the idea that symbiosis between one ancient prokaryote inside another drove
the evolution of eukaryotes. We’ve discussed endosymbiosis in its own
episode, and you may have noted that it plays a recurring role in the lives of microbes
we’ve covered. This theory is now so well understood, and
it has so much explanatory power that, at this point it feels like a thing that we’ve
kinda always known. But, indeed, the battle over the acceptance
of endosymbiotic theory was still going on during my lifetime. I remember being taught that this was probably
a thing, not that it definitely was. In her paper, Margulis also notes that she was
not the first scientist to consider the role of symbiosis in evolution. The theory was first proposed by the Russian
botanist Konstantin Sergeevich Mereschkowski in 1905, and later scientists had suggested
that the resemblance they observed between certain eukaryotic organelles and certain
prokaryotic organisms was more than just coincidence. But while these bits and pieces of endosymbiotic
theory had been around before her, Margulis was the one who tied them together. “On the Origins of Mitosing Cells” focuses
on three examples of what Margulis thought were possible endosymbiotic events: the evolution
of mitochondria, chloroplasts, and flagella from potentially prokaryotic origins. While the paper didn’t describe any experiments
of her own, she drew on the works of her predecessors to provide experimental evidence for her ideas. She also described predictions for future
experimental results that would support the theory. The result was a paper that didn’t just
present an argument, it laid out a multi-chapter story of evolution that drew on Margulis’
understanding of biology and even atmospheric chemistry to describe how symbiosis may have
driven eukaryotic evolution, and how scientists might be able to verify that story. This paper, “On the Origin of Mitosing Cells”
was rejected more than a dozen times until it was finally published in the Journal of
Theoretical Biology. And her paper caused quite a stir, highlighted
and debated in both popular and academic formats. Some scientists were just as captivated by
the idea of endosymbiosis as Margulis was. Others dismissed her theory outright. In a paper called “The non symbiotic origin
of mitochondria,” the authors wrote that “while the symbiotic theory may be esthetically
pleasing, it is not compelling.” But while the conversation may have become
contentious, Margulis stuck to her theory. To her, the notion that these organelles could
have evolved solely through the accumulation of thousands of mutations was both improbable
and unsupported by the evidence. Slow change was part of the evolutionary story,
but it was not all of it. And she thought symbiogenesis would explain
these more immense changes that were necessary to the history of eukaryotes. And so Margulis continued to experiment with
her microbes and investigate the limits of her theory. But so did many others. In 1978, Robert M. Schwartz and Margaret O.
Dayhoff published “Origins of Prokaryotes , Eukaryotes, Mitochondria, and Chloroplasts,”
which was able to experimentally conclude the prokaryotic origins of chloroplasts and
everyone’s favorite powerhouse, the mitochondria. This work was among several that would confirm
that Margulis was right about those two organelles in particular. But as important in science as what you get
right is what you get wrong. No experimental evidence has turned up to
support Margulis’ theory that the flagella that help many eukaryotic organisms move were
originally an organism of their own. She thought they may originally have been
spirochetes. But while flagellates and other aspects of
her theory have not panned out in experimental testing, Margulis would continue to defend
her ideas. Lynn Margulis eventually moved to the University
of Massachusetts Amherst, where she would stay until her death in November, 2011. In an interview she gave to Discover Magazine
only a few months before she died, she said, “I don’t consider my ideas controversial. I consider them right.” It’s a statement that may seem admirable when quoted against the history of endosymbiotic theory. But in that same interview, Margulis insisted
that AIDS is not caused by HIV, it’s caused by a syphilis-causing spirochete that has somehow
been rendered undetectable to all scientific and medical scrutiny because of...symbiosis? We’re not gonna litigate her statement here because
there’s no point in that: at the time she gave the interview, there had been decades
of research connecting AIDS to HIV, as well as decades of real-life suffering and death
caused by the virus. But this wasn’t the only time Margulis engaged
in what some might euphemize as “controversial opinions,” but that at times took her fully
into conspiracy theories. Lynn Margulis’ work was part of a long history
of contrarianism that often appeals to us because when they get things right, contrarians
push through established beliefs to reveal hidden mechanisms of the world. But when they get things wrong, they do so
at the expense of scientific rigor, intellectual honesty, and just plain old decency. And so it can sometimes be unclear how to
understand and process their work, unless--perhaps--we take inspiration from Margulis’ fascination
with microbes and the communities they form. Just as the light we shine through our microscope
informs the colors and structures that shine on the other side, our understanding of the microcosmos is shaped by the people who study it. Their experience, their personalities, their
biases—these all shape the questions they ask, the ways they ask them, and the conclusions
they draw. And so, science is at its strongest when,
like the symbiotic microcosmos that entranced Margulis, it is understood not as the product
of a single expert but as a collective expertise—the result of shared experiences that are constantly
in conversation with each other. That is what made “On the Origin of Mitosing
Cells” so powerful—the way Margulis so effectively synthesized her ideas with other
scientists’ work to describe a whole history of evolution that, while not without its flaws,
provoked a dialogue that altered our understanding of biology and of the history of life on earth. And this impact makes the frustrations of
her legacy all the more acute. Margulis would continue to draw on what she
learned from the world of microbes, co-authoring a number of books with her son Dorion Sagan
that brought the wonders of microbial evolution to a wider audience. In one of their books titled Microcosmos,
they wrote: “It is tempting, even for scientists, to get carried away by success stories.” It’s a sentence that, against the backdrop
of both her scientific and unscientific efforts, reminds us that microbes can teach us a lot
about the world, but that there is also a limit to what we learn. And often, that limit is our own selves. Thank you for coming on this journey with
us as we explore the unseen world that surrounds us. Thank you as well to all of the people on
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you love, so that it will continue existing. So thanks to all of them for helping make
this continue to happen. What great folks. If you want to see more from our Master of
Microscopes James, check out Jam & Germs on Instagram. And if you want to see more from us, there’s
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