Lynn Margulis – the Rebel of Evolutionary Biology

By Jaime Seltzer

“The view of evolution as a chronic bloody competition among individuals and species, a popular distortion of Darwin’s notion of “survival of the fittest,” dissolves before a new view of continual cooperation, strong interaction, and mutual dependence among life forms. Life did not take over the globe by combat, but by networking. Life forms multiplied and complexified by co-opting others, not just by killing them.” – Lynn Margulis

“I don’t consider my ideas controversial. I consider them right.” – Lynn Margulis

Lynn Margulis was a biologist, a geneticist, and an expert in evolution; she was also a fighter at heart, someone who did not fear taking on established principles and ideas.

Lynn was born in 1938, and grew up in a pretty rough part of Chicago. She proved to be quick and clever at a very early age, graduating from the University of Chicago with her bachelor’s degree at age eighteen. It was a very exciting time to be in the biological sciences: Watson and Crick (and Franklin, and Wilkins) had just proved the structure of DNA was a double-helix. In graduate school, two of Lynn’s professors at the University of Wisconsin at Madison discovered DNA in chloroplasts, the cell organelles responsible for photosynthesis; and others had found DNA in mitochondria. Though the fact that mitochondria and chloroplasts contain DNA is accepted now, many scientists disputed the work at the time. All of this primed Margulis for her controversial Ph.D. topic at the University of California at Berkley: symbiosis.

In the 1920s, a microbiologist named Ivan Wallin proposed the idea that chloroplasts and mitochondria might actually have been entirely separate organisms before the cell’s evolutionary history and the tiny bacteria’s collided. He had little evidence for the fact other than that mitochondria and chloroplasts were about the same size and shape as certain kinds of familiar bacteria, and so was laughed out of the figurative room.

Her paper was rejected fourteen times before being accepted by the Journal of Theoretical Biology in 1967. Today Lynn’s theory of the development of modern eukaryotic cells, called endosymbiosis, is found in every modern biology textbook.

Margulis took up the challenge of proving that this was actually the case. She laid out a rationale for her idea that went something like this: Billions of years ago, the only living things on planet Earth were anaerobic bacteria – that is, bacteria that did not need oxygen. This was good, since there was none to be had; when Margulis postulated her theory there was good evidence that the Earth had existed for a long period of time without oxygen gas making up a significant percentage of the atmosphere. Then, a new type of microorganism came on the scene that released oxygen as one of its byproducts as it produced sugars, in a process similar to photosynthesis. This microorganism was so successful that it reproduced in huge numbers, and bit by bit, the percentage of oxygen in the air crept upward.

Despite our desperate need for it, this was not a good thing for the bacteria that had been there, first. Pure oxygen is reactive and damaging to cells, and is linked to the aging process as well as the progression of many different diseases in human beings. The original bacteria began to die off.

Now here’s where it gets interesting! Margulis’s theory then describes a third type of tiny bacteria that began to evolve. Instead of releasing oxygen as a byproduct to make sugars, they absorbed oxygen to break down sugars. Over the course of this process, they made ATP, a chemical with high-energy bonds that could be broken whenever the cell needed to do something, like opening up a fresh package of batteries.

Then, something strange and unusual happened.

The tiny bacteria that made ATP tried to invade one of the ‘old’ bacteria that could not survive in the oxygen-rich environment; but the old bacteria couldn’t quite digest its invader, and the invader couldn’t quite destroy its host. So they sat there together in what one might imagine as considerable consternation, each unable to kill the other and unable to leave – much like you and your sibling in the back of your car on a long road trip.

Lynn Margulis

Lynn Margulis and her card in Women in Science.

However, as the old bacteria were exposed to too much oxygen and died horrible, apoptotic deaths, the Frankensteinian cell was at an advantage: it had a little passenger that kept sucking up that oxygen, detoxing the cell. Throughout this process, it made energy molecules, which the host cell got to use as well sometimes. The invading bacteria got some benefit, too: it was protected from the ravages of the outside world. Eventually, the chemicals that signaled cell division for one cell signaled the other cell to do the same, simultaneously, and you had a sort of cell-within-a-cell that was… permanent.

Margulis’s contention was that the big cell became all cells that had organelles (known as ‘eukaryotic’ cells) and the little cell became the mitochondria in animals and the chloroplast in plants. She took her theory even further and stated that perhaps all evolution was similar – that is, occurring within the framework of living beings benefitting one another rather than in constant, bloody competition. After all, if the human body is composed of ten times as many bacterial cells as its ‘own’ cells (true fact!) – if, without those cells you would be unable to think, unable to digest, in short, unable to live – then what is to say what is ‘you’ and what is ‘them’?

She was totally right about everything except maybe that last bit; and that last bit is still up for debate, not proved incontrovertibly wrong.

But now imagine trying to publish something so revolutionary.

Lynn could have taken her ideas to a novel or gone to the countryside to keep bees after the first five times her Ph.D. paper was rejected by a scholarly journal. Instead, she kept trying and trying. She knew her theory was correct, and she knew she’d done the legwork to provide good evidence. She would not be stopped by something so pedestrian as a hidebound peer review board whose members were used to comfortable and well-worn paths of thought. Her paper was rejected fourteen times before being accepted by the Journal of Theoretical Biology in 1967. Today Lynn’s theory of the development of modern eukaryotic cells, called endosymbiosis, is found in every modern biology textbook.

Lynn went on to help develop Gaia Theory – the far less well-accepted but intriguing notion that all life on earth is part of one, contiguous ecosystem. Some took the Gaia Theory further and postulated that the earth itself is one organism. If mitochondria could become part of a living cell, they argued, what was to say that all organisms were not part of one, larger organism? Margulis tended to stick to the first definition, however, rather than the latter, which is more in the realm of philosophy than science.

She was famously contemptuous of other evolutionary biologists, in part because of their sole focus on the evolution of animals and in part because of their linear manner of thinking. “The evolutionary biologists believe the evolutionary pattern is a tree,” she said. “It’s not. The evolutionary pattern is a web – the branches fuse.

Finally and interestingly to modern medicine, Margulis had theories about spirochete-caused illnesses such as Lyme disease and syphilis, postulating that they could go into a dormant state. The debate about Lyme in particular is relevant to modern medicine. The conception is that Lyme can be defeated with a course of antibiotics, but for some patients, symptoms last long after treatment. Margulis’s explanation that the two spirochetes have co-evolved with humanity in such a way that they are adapted to avoid decimation is an interesting hypothesis that might explain this phenomena.

Hagen, J., Allchin, D., & Singer, F. (2009). Doing Biology (pp. 23-36). Glenview, IL: Harper Collins. Retrieved from
Teresi, D. (2011, June 17). Discover Interview: Lynn Margulis Says she’s Not Controversial, She’s Right. Discover Magazine. Retrieved October 2, 2015, from
Weber, B. (2011, November 24). Lynn Margulis, Evolution Theorist, Dies at 73. In The New York Times. Retrieved October 2, 2015, from

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