In terms of cell count, ninety percent of you isn’t you at all. Bacteria, though by mass they only make up about two percent of a human being, account for nine out of every ten cells inside you. Some of them are beneficial, like the bacteria in your digestive system that help break down carbohydrates. Others, less so, like the mouth bacteria that form part of tooth plaque. We live in a constant state of symbiosis with trillions upon trillions of unicellular organisms within, and life could not be what it is without them. It’s an unsettling thought for those who like to classify humans as somehow Outside Nature, but odder still is the fact that even those few cells we recognize as “human” are themselves a crazy quilt of ancient compromise and conquest.
We are deeply foreign to ourselves, an insight we owe to unicellular biologist Lynn Margulis (1938-2011). Outspoken, aggressive, self-professedly arrogant, she was the only person with the imagination to successfully resurrect the late 19th century theory of endosymbiosis, the knowledge to back it up with an overwhelming array of data from the world’s leading microbial research and micropaleontology centers, and the nerve to press its case again and again in the face of monumental institutional resistance. She was born Lynn Petra Alexander to a Zionist Jewish family and was, even as a child, completely a creature of her own will. In school, she grew tired of the incessant and difficult algebra of the University of Chicago eighth grade laboratory school, and so decided to bluff the local public high school into accepting her, attending for a month until her deception was discovered and her parents, presented with the fait accomplit, decided to let her continue at the less demanding public school.
Through pure stubbornness and will, Margulis had earned herself a spot with the older but less gifted children, and relaxed into the lessened expectations. In tenth grade, her advisers showed her that, in both mathematics and vocabulary, she was performing at lower levels than she had as an eighth grader. She had essentially spent two years regressing in ability, but made it into the University of Chicago’s early entrant program anyway, attending college in her mid teens to follow a nondescript liberal arts education. Which was when a charismatic nineteen year old graduate student entered her life.
His name was Carl Sagan.
He was all confidence and passion, and his enthusiasm for science infected her. He introduced her to the emerging field of genetics, and she made the decision to divert her studies towards biology and herself to the role of wife. Lynn and Carl were married in 1957, when she was nineteen and he was twenty-two. It was not to be a happy union. Sagan expected Margulis to manage all of the household affairs and did not take contradiction well. He was physically and verbally abusive. She later explained that she had married him as the best way to get out of Chicago, a city she could no longer stand. The chance came when she was offered a position to work on her PhD at Berkeley studying microorganisms. Somewhere between the cooking and cleaning, the child-rearing and the abuse, she began looking into a long-discredited theory about the origin of cell organelles, endosymbiosis.
This theory dates back to 1883, when the botanist Andreas Schimper, who gave chloroplasts their name, hypothesized that they might have once been free organisms that had been taken up by bacteria long ago in the deep evolutionary past. Paul Portier added mitochondria, the ATP producing powerhouses of eukaryotic cells, to the list of probable symbiotes in 1918, but then interest in the idea faded. The Darwinists were uncomfortable with the idea of new species forming by the incorporation of other life forms, and the public, only recently turned onto the idea of bacteria as the cause of disease, couldn’t find its way to considering them as having played, and continuing to play, a beneficial role in the evolution of life.
In 1966, Margulis wrote up a paper, “On the Origin of Mitoting Cells” which sought to combine the old idea of symbiogenesis with new insights into the structure and genetics of unicellular organisms. It was turned down fifteen times before it was finally accepted by a theoretical biology journal. Margulis’s Serial Endosymbiosis Theory (SET) underwent a few changes over the years, but retained the same basic shape: about two billion years ago, acidophilic bacteria started engulfing and incorporating quick spirochetes, corkscrew like bacteria which, when attached to the bacterium’s membrane, allowed it to travel faster and further in search of new food sources. At the same time, the incorporation of that foreign organism prompted the cell to wall off its genetic material in a protective nucleus, creating the first nucleated organisms.
Meanwhile, as cyanobacteria grew and flourished, they filled the atmosphere with toxic oxygen gas, and a new form of bacterium arose that had the ability to not only survive in the presence of this violent gas, but to harness it to create energy in untold amounts. The spirochete-acidophile bacteria that incorporated these oxygen-consuming bacteria gained a substantial advantage in energy efficiency, and thus it was that mitochondria came to be. A bit later still, photosynthesizing bacteria were absorbed as well, providing the basic components of the modern cell: cilia to move, mitochondria to create energy from oxygen, and chloroplasts to create sugar from sunlight.
If you were a biologist who believed in the steady accumulation of evolutionary changes through DNA mutation, Margulis’s theory sounded wildly heterodox. Neo-Darwinism maintained that organisms adapted by accumulated DNA mutations and their subsequent phenotypic variations. Then, out of nowhere, this bacteriologist started talking about wholesale genetic swapping and even complete incorporation. It was rank heresy, and remained as such until nucleic acids saved the day. The genetic material contained in chloroplasts and mitochondria was found to be more similar to that of free bacteria existent today than it was to the nuclear DNA of the cell it was extracted from. That could only be the case if those two organelles were once free-roaming. As regards these cellular components at least, Margulis’s theory is now the standard one, found in any high school textbook, even as the question of spirochete uptake is still controversial.
While she was fighting for due consideration to be paid to her theory on the origins of the eukaryotic cell, Margulis’s personal life proceeded along its rocky path. She divorced Sagan in 1965, then married crystallographer Thomas Margulis in 1967, only to divorce him as well in 1980. She would not remarry, finally having learned that the dual life of wife and scientist wasn’t one she was temperamentally able to live. Science it was to be.
Which was fortunate, because no sooner had she stirred up the controversy over SET than she set about advocating a perhaps even more maligned notion, James Lovelock’s Gaia Theory. Lovelock had proposed his theory in the mid Sixties, and it is still among the most consistently misunderstood of principles. Part of the misfortune lies in the naming. Lovelock had asked his friend, William Golding (author of Lord of the Flies) for a name that was catchier than his “cybernetic system with homeostatic tendencies as detected by chemical anomalies in the Earth’s atmosphere.” Golding came back with Gaia Theory, which was certainly snappy and easy to grasp, but which also had connotations with New Age frippery that Lovelock and Margulis spent their whole lives combating.
The theory came from Lovelock’s work for NASA developing a system to detect life on Mars. He began by looking at Earth’s atmosphere, to see what it was about it that indicated living beings, and noticed several startling things, namely that we have a lot of gases in high concentrations that oughtn’t be there. Oxygen is super reactive, and in an inorganic atmosphere would deplete itself quickly upon production, but on Earth we maintain a pretty steady 20% in our atmosphere. The only way for that to be the case is if it is constantly being replaced by some living system. Likewise, Lovelock investigated methane, and asked Margulis if she could find an explanation for its steady presence in the atmosphere. She, drawing on years of unicellular organism research, pointed out the global contribution made by bacteria in the guts of cows and termites to methane production.
Together, the two talked about the anomalous nature of Earth’s atmosphere, how life on the planet appeared to have some overall homeostasis that kept the brute matter of the Earth in precisely the proportions needed for the continued support of life. They investigated the interface of life, the atmosphere, and geology, the tumble of different ecosystems against each other. Gaia was for them, “An emergent property of interaction among organisms, the spherical planet on which they reside, and an energy source, the sun,” and, “A convenient name for an Earthwide phenomenon: the regulation of temperature, acidity/alkalinity, and gas composition. Gaia is the series of interacting ecosystems that compose a single huge ecosystem at the Earth’s surface. Period.”
To modern eyes, this is a relatively uncontroversial position. Life changes the composition of the atmosphere, which in turn affects which organisms prosper and which do not, which in turn puts homeostatic limits on just how far the world system can veer from one that supports life. Living things, in their statistic rise and fall, mechanically create and maintain the conditions for further life. At the time, however, the association of Gaia with unscientific Mother Goddess theories, and the wording that Lovelock and Margulis chose, opened the door for skeptics to accuse them of promoting an Intentionalist Nature that somehow chose conditions just right for life out of some unknown and unknowable favoritism.
In between wrangling over SET and Gaia Theory, Margulis had a go at rewriting the taxonomy of nature. As an endosymbiosis theorist, she logically had issues with the standard Tree of Life picture of the natural world, which showed gradual mutations from a primal source and allowed for no exchanges of genetic material between branches, as she knew happened not only among the unicellular animals she studied, but in the communal life forms whose unique stories she collected from her web of biological correspondents. Almost entirely ignoring the mounting insights of molecular biology, she created a new system of five kingdoms branched into two superkingdoms organized around the observations of endosymbiosis and allowing for constant genetic exchange, a view enshrined in her Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth. According to Michael Chapman, who worked with her on the fourth edition of that book, hers was a cell-first perspective that stuck by its observational guns even when genetic sequencing contradicted her.
That’s who she ultimately was. In her quasi memoir, Symbiotic Planet, she dryly confesses, “Some colleagues label me combative; others, unfair. Some say I only collect relevant work and unfairly ignore contradictory data. These accusations may be correct.” For four decades, she held onto massively unpopular theories grounded in unicellular insights she knew to be sound, and shepherded them into the mainstream. She argued down Ernst Mayr, Richard Dawkins, and a bristling squadron of neo-Darwinists besides to get SET a place in the textbooks, and learned from the experience perhaps unfortunate lessons about the hazards of compromise. But she gave us a bit of delicious discomfort with our own fundamental hybrid oddness, and humanity is at its very best when squirming, after all.
FURTHER READING: Lynn Margulis’s life is astoundingly difficult to piece together for somebody so important to the history of biology. Symbiotic Planet starts off with some genuine bits of autobiography, but abandons those around the year 1960 to give more space over to her three main areas of contribution: SET, taxonomy, and Gaia. To find out the rest of the story, her son Dorion edited a collection of essays, Lynn Margulis: The Life and Legacy of a Scientific Rebel, which is, like Symbiotic Planet, great for if you want explanations from several different scholars about the origin and development of SET or Gaia, not so great if you want a straightforward biography of where she was and what she was doing at any given year. Ironically, the best place for that, at least until 1965, is contained in the interviews Keay Davidson collected for Carl Sagan: A Life, a great book which contains details on the tribulations of their marriage which aren’t contained elsewhere.