“For as long as I can remember, when someone asked me what I wanted to do when I grew up, I answered, ‘an explorer and a writer’. An explorer of what?...’Whatever needs exploring,’ I said without hesitation.”

- Lynn Margulis

As a science writer, I spend many days poring over literature, talking to scientists, and sitting in on lectures; looking for common threads, for trends, for flips in perspective that could open up new possibilities. For both science writers and theoreticians, our job is to organise observed facts into stories. Doing so requires a veritable rolodex of role models, of people whose moves we can emulate and apply to a different field.

Being a woman adds a whole second dimension to the problem. In biology, the science I cover, there are very few female theoreticians. Biology history recognises a handful of women as stellar experimentalists and legendarily persistent truthseekers — women such as Rosalind Franklin (who did most of the heavy-lifting in the discovery of DNA’s structure), Barbara McClintock (who discovered genes that “jumped” or relocated themselves within the genome), and Elizabeth Blackburn (who discovered the protective telomere caps on the end of every chromosome). As much as I admire those women, I’m nothing like them. I’m too much of a flibbertigibbet, too prone to skipping from one topic to the other and making grand assumptions that drive the stories I assemble from facts. In short, I’m not an experimentalist. Insofar as I’m like a scientist, I’m more like a theoretician.

When biology recounts its grand theoretical breakthroughs, the scientists responsible are distinctly male. There are the founders Darwin and Mendel, the statistician wunderkind J.B.S. Haldane, opposing firebrands Richard Dawkins and E.O. Wilson, theory unifiers such as Ernst Mayr, and many more.

But there is one woman whose contributions to biological theory stand out, and her name is Lynn Margulis.

“Life on earth is more like a verb. It repairs, maintains, re-creates, and outdoes itself.”

- Lynn Margulis

Lynn Alexander was born in Chicago, lllinois in March of 1938. “When I was a kid, I never believed what they told me,” she said in an interview for the Research Channel. “I believed what I saw myself.” After struggling in mainstream public schools, her parents transferred her to the University of Chicago Lab School, a school that required students to read the original texts of Isaac Newton and Gregor Mendel. “Classes were not required; that’s why I went to them all,” she said.

After high school, she continued on to college at the University of Chicago, where she met a young physics graduate student named Carl Sagan. The two married in 1957. “He was instrumental in that he showed me that people could actually do science,” she later said.

Lynn continued her studies in genetics and microbiology at University of Wisconsin-Madison, and later at University of California, Berkeley. She earned her PhD at the age of 27 in 1965. By then, she and Sagan had divorced. She soon remarried, this time to a crystallographer named Nick Margulis. Still, Lynn’s career steamed forward with a lectureship at Boston University.

She had become fascinated with an oft-ridiculed hypothesis called “serial endosymbiosis,” which surmised that mitochondria, chloroplasts, and other cellular organelles might be descended from bacteria that had been devoured by other single-celled organisms and somehow survived within the organisms’ bodies.

Just two years later, in 1967, she dropped “Origin of Eukaryotic Cells” (which she expanded into a book in 1970), considered the cornerstone of the theory of symbiogenesis, which holds that we owe our cellular complexity to bacteria. Specifically, hundreds of millions of years ago, one prokaryotic archaea engulfed a bacterial prey; instead of succumbing to digestion, the bacteria survived, reproduced, and began providing that archaea with an energy source. Instead of survival of the fittest, two species merged to become an entirely new super-kingdom.

Margulis wasn’t the first to hypothesise that our energy-generating mitochondria and plants’ photosynthetic chloroplasts might be descended from bacteria, but those earlier claims were highly speculative. Margulis was the first to provide a rigorous array of evidence for it: Before Margulis, most biologists had assumed that the bits of DNA floating around outside cells’ nuclei were just genetic flotsam and jetsam with no purpose. However, analysis of DNA from chloroplasts and mitochondria revealed surprisingly bacteria-like miniature genomes. Decades of mitochondrial genome sequencing have bolstered the claim that mitochondria are descendants of ancient bacteria.

Symbiogenesis is an origin story that takes the stereotypical evolution story – of life-and-death struggles which gradually build to the dominance of the fittest – and flips it on its head. Now a life-and-death struggle is disrupted by a fusion of two life forms, both of which are forever changed by the encounter. Margulis’ biology wasn’t about cycles of domination; it was about relationships between organisms.

Her work also flew in the face of decades of feminist critique, which argued that science, shaped by masculine Enlightenment ideals, is all about dominating nature, penetrating its mysteries, revealing its secrets, and using those results as a way to control threats and establish civilisation’s dominion over the world. Margulis’ biology, in contrast, was about engulfment, immersion, and mutual change. She was the biology establishment’s favourite radical.

For me, discovering Margulis’ work as an undergraduate student was a revelation. Many scientists quote the adage “question everything,” but few live up to it as thoroughly as she did. Later in her career, Margulis began to reject notions of symbiosis as “mutually beneficial,” because that language reduces the relationship between organisms to a cost-benefit analysis. Being her usual cheerfully radical but rigorous self, Margulis objected to depicting ecology as a zero-sum game. “I was taught over and over again that the accumulation of random mutations led to evolutionary change – led to new species. I believed it until I looked for evidence,” she wrote.

In the short film Looking Through the Microscope with Lynn Margulis, Alex Salhany, a former undergraduate researcher in her lab, tells a story of one Saturday night working late. He wanted to leave and meet up with a girl. Salhany recalls the incident with a smile on his face. “She said to me, ‘Alex, when you want to stay and sit on a Saturday night and look at the organisms just as much, if not more, than you want to chase after pretty girls, then you’ll be a scientist!’” And for her, it was true. “The passion that she had showed through in all of her work,” Salhany concluded.

When the English chemist James Lovelock began to write about a provocative idea called the the Gaia hypothesis, Margulis was one of the first to investigate and defend the concept. The Gaia hypothesis holds that the Earth’s entire biosphere acts as one interconnected organism of planetary size. Some scientists wanted to reject or disavow Gaia hypothesis, not because of a lack of evidence — there’s a lot of evidence for life reshaping abiotic conditions — but because it sounds too hippie-dippie. Gaia can appeal to people who don’t like science and who seek to imbue nature with a sense of unified purpose. While extreme purposeful Gaia hypothesis is somewhat out there, the moderate, interconnected Gaia theory isn’t. All forms of life — plant, animal, bacterial, fungal, and the none-of-the-aboves — can affect atmospheric and geological chemistry on a massive scale. Hence, for example, the recent rise of the hybrid field biogeochemistry.

Margulis died in 2011, at age 73, while I was still an undergraduate. She’ll always be one of the scientists I most regret never getting a chance to meet.

Margulis herself once wrote that she dreaded being labeled a role model, a title that seemed to imply a superwoman-like ability to balance work and family. In fact, she thought of herself simply as a woman who spent Saturday nights hanging in, reading and working on science, forsaking many of the social and familial obligations that most women feel in order to pursue her intellectual work.

However, in Lynn Margulis, I see many qualities to emulate. Her empathy was expansive, so expansive that it encompassed microbes. She wrote essays with titles like “Power to the Protoctists” and “Prejudice and Bacterial Consciousness.” Her work challenged the notions put forward by neo-Darwinists such as Stephen Jay Gould, who argue that random, incremental mutation is the primary driver of evolutionary change. Margulis countered that sudden leaps into symbiosis could have an even larger effect on evolutionary history. She even posited that serial endosymbiosis — the accumulation of collaborations and interactions between species — could be the most important force in evolution.

For most of my academic life, I thought there was something paradoxical about being interested in both humanities and biology, as if my interest in literature and social theories would somehow undermine my thinking about cells and ecology. But Lynn Margulis’ approach embraces ideas from both within and outside of the traditional sciences. Most importantly, her work showed me that a woman’s voice could be just as valuable in the theory side of biology as in the lab. Her boldness mixed with empathy, and her factual rigour mixed with imagination are traits we all can learn.