Imagine a raging planet, with active volcanoes spewing lava and gases, meteors constantly falling and thunderstorms of strong electrical apparatus. Then, tiny beings that were capable of living in such a hostile environment began taking hydrogen from water and expelling oxygen as waste, an enormously toxic gas that caused a veritable worldwide holocaust.
Subsequently, some of the inhabitants of this place developed mechanisms to decontaminate themselves and take advantage of the dangerous element. This story full of adventures happened on our planet about 3900 million years ago, and its protagonists, bacteria, offers us many clues about the mystery of the origin of the current forms of life.
In 1967 an American magazine published "The Origin of Mitosis in Cells", an article that had previously been rejected fifteen times in prestigious scientific journals. Its author, who signed at that time as Lynn Sagan due to her first marriage, was a short and restless woman, who thanks to her amazing tenacity managed to question the prevailing neo-Darwinian theories of the time and to turn the understanding of the evolution of the species upside down.
Those who knew her highlight her friendly nature and her willingness to exchange ideas: "she was fascinated by any story that one told her", recalls Juli Peretó, a researcher at the University of Valencia and a friend of the scientist. "Whenever she came to Spain she asked me to explain what we were working on, and I took advantage of any opportunity to share ideas and news. Her curiosity was not only scientific: she would taste all sorts of different foods in the restaurants she visited and was always interested in how the chefs prepared these dishes. She would always get in touch with locals when travelling an made a special effort to get to know the people that lived in that place.
Indeed, the American biologist's boundless curiosity led her to defend the "Theory of Serial Endosymbiosis" and in turn to explain the origin of the eukaryotic cell. Let's see what this theory consists of.
Bacteria eating bacteria or the great leaps of evolution
Darwin himself in his famous book The Origin of Species pointed out some of the apparent inconsistencies that his theory was unable to explain. If, according to him, evolution worked through an accumulation of small gradual changes that are fixed as characters by natural selection, how was it possible that neither in the fossil record nor in current organisms were these intermediate forms found? One of the most obvious abrupt transitions can be seen in the differentiation between prokaryotic and eukaryotic cells. While eukaryotes possess a nucleus, a cell structure that encloses the genome in a membrane envelope, in prokaryotes the genetic material floats freely through the cell. And there are no intermediate forms: you are either eukaryotic or prokaryotic.
While the neo-Darwinists tried to defend their position, Margulis began to dive into literature and rescued, adding new evidence, the theory of symbiosis that Merezhkovsky had put forward forty years earlier. According to this hypothesis, eukaryotic cells would have originated from different prokaryotic cells through a symbiotic relationship that became stable.
In other words, one bacterium would have literally engulfed another, and over time these interspecies consortia became permanent. The evolutionary force which generated this new type of cell was not the accumulation of small mutations, but rather a sum of complex structures which already existed previously. Despite the initial reticence with which the scientific community accepted these ideas, over time experimental evidence has accumulated which has confirmed them.
Margulis wanted to apply symbiogenesis to the origin of all species. For her, life on Earth was the result of a symbiosis of organisms, everything was symbiotic, and in her publications, she gave abundant examples to prove her theories. This is the case of the cow, which can digest cellulose thanks to the microbial symbionts housed in its stomach, or of the fish that live on the seabed and host bacteria that glow in the dark. "We often associate the word bacteria or microbe with disease, when it is just life: you are a walking sack of bacteria," he once told an interviewer.
Indeed, Margulis became the most ardent defender of microorganisms and devoted hundreds of pages and lectures to claiming their fundamental role in the evolution of life and the world we inhabit today. "Bacteria were the inventors, on a small scale, of all the chemical systems essential to life," she says in the book Microcosmos, written with her son Dorian Sagan. "This ancient and high biotechnology led to the development of fermentation, photosynthesis, the use of oxygen in breathing and the fixation of atmospheric nitrogen.
He criticized the conceited postures that place the human being at the centre of the world or that interpret evolution as a path from the lower beings (bacteria) to the higher beings (man). Her obsession with the microbial universe took her to the extreme of "keeping in her purse, along with the photographs of her children, images of her favourite protists," said Antonio Lazcano Araújo, a professor at the National Autonomous University of Mexico and a collaborator of the scientist. He was right: bacteria today inhabit every environment imaginable, from the acid tanks of chemical companies to the extremely salty waters of the Dead Sea. For two billion years, bacteria exclusively populated the Earth, and in the event of some kind of nuclear catastrophe, they would probably also be the only survivors.
The brilliant scientist was clear: "There is no particular species that is the centre of life, we can cause our own extinction, but not that of all life on the planet. Life existed without us... and will continue without us, self-regulating". This concept of self-regulation on a planetary scale is closely linked to the theory of her colleague Lovelock, the so-called 'Gaia Hypothesis', which Margulis helped to develop. Despite the spiritual connotations that the word 'Gaia' may have, a term from the ancient Greek meaning 'Mother Earth', Margulis always insisted that it was a way of synthesising a broader concept. To refer to the planet as "a feedback system with homeostatic tendencies detected from chemical anomalies in the Earth's atmosphere" was simply long and tedious. Our Earth, Gaia, is a network of ecosystems, a biological construct whose atmosphere has been produced, maintained and transformed by the metabolic processes of the biosphere.
In this world of biological interactions and self-regulating ecosystems, new technologies invented by man may seem out of place. This was not the view of the scientist, who recognized that technology is already part of the human strategy for survival. "We are already superorganisms," she once commented, "because we need external factors to survive (electricity, oil, gas...). Everything comes to us through networks, and we are the nodes of those networks".
The scientist compared human beings to pioneer species, which are defined in ecology as those that expand and colonize new habitats quickly, grow without measure and transform their environment at great speed. However, she warned, "in many cases, this rapid expansion of pioneer species leads to their own disappearance. We do not know if we will become a climax community or a simple transitional pioneer species. But whatever it is, our destiny will be inseparable from that of our technology.
However, Margulis did not include the television in this technology, which is so essential for human beings. "She was totally against television, she said it was one of the worst enemies of culture," explains Juli Peretó. "Once she came to Valencia to present one of her books and made a little mess with the cameras, she didn't let them film her, only her voice. Imagine the scene, all the cameras were pointed at the ceiling and she was talking into the microphones. Even though she was a woman of affable character, on that occasion she got quite angry, she made a whole plea against television".
Iron fist with a silk glove
An ardent defender of her ideas, Lynn Margulis was the subject of many scientific controversies. "She didn't mind taking on everyone if she had something clear," explains Antonio Camacho, a researcher at the Cavanilles Institute of Biodiversity and Evolutionary Biology (Valencia) who agreed with Margulis on many occasions. "But he did so with absolute elegance. He overwhelmed you with a multitude of examples and case studies, it was obvious that he documented himself a great deal to defend his ideas. He was the perfect example of the use of the 'iron fist with silk glove'. The fist was his devastating argument and the glove his way of debating. He never personalized his rivalries, I think it was very difficult for anyone to be offended when Margulis criticized him.
The truth is that Margulis came to defend very controversial positions. For example, the biologist said that it was not clear that HIV caused AIDS, and that the disease could be a form of syphilis. She was famous for her questioning of the origin of the 9/11 attacks and believed that the collapse of the buildings was due to "a carefully controlled explosion with powerful explosives that would have been set many weeks, or months, earlier.
He also claimed that the only microorganisms that can harm us are those that share an evolutionary history with us, that is, those that would have participated in the process of symbiosis to give rise to our species. Although his theory about the origin of the eukaryotic cell through endosymbiosis is already fully accepted in the scientific community, Margulis was of the opinion that absolutely all speciation processes originated through this mechanism. She maintained that natural selection was only the way to eliminate genetic errors, but that it could not generate novelty and therefore was not a key force for the emergence of new species. "I don't consider my ideas controversial, I consider them correct," this woman, who was undoubtedly clear on the matter, stated emphatically.
Being a woman in a man's world
Margulis began her scientific activity in the 1960s, a time when research, like many other disciplines, was predominantly the domain of men. "Despite being 22 and already the mother of two very active children, my enthusiasm for cellular genetics and evolution exceeded any thought of becoming a full-time housewife," she said of her time in the genetics department at the University of Berkeley.
Although hers is one of the first female names to appear in biology textbooks, Margulis acknowledged that she never had any problems due to her status as a woman. "One night during a period at Caltech," she explained in an interview, "I heard women tell horrible stories about their situation, but I can't say the same thing happened to me. I think the problem is not between the sexes, but between people who don't know anything beyond their field.
Indeed, Margulis was highly critical of this deeply segmented way of doing science, so that specialists in one area know nothing about what is being done in others. "She was very interested in the connection between the disciplines and the various manifestations of nature. It was, in a way, holistic," explains Ignacio Bayo, a popular scientist who dealt with her on numerous occasions. "All our conversations revolved around the work but always from a very broad perspective". He spoke of "scientific tribalism" and warned that this fragmentation made the advancement of knowledge extremely difficult.
He preached by example: a doctor in genetics, he was interested in the ecology, evolution and taxonomy of microorganisms. Her studies led her to propose the classification of living beings in the five kingdoms that today is studied in almost all institutes. At the age of seventy, this woman of inexhaustible energy worked until the end of her days in the Department of Geosciences and the Division of Life Sciences of NASA financed her research. She was a member of the National Academy of Sciences in the United States and a Foreign Member of the Russian Academy of Natural Sciences, in addition to seven honorary doctorates.
In spite of her prolific scientific activity, Margulis was able to reconcile her family life and her work perfectly, mixing it up on many occasions. "She treated her children as if they were students and her students as if they were her children," said Dorion Sagan, the result of the scientist's first marriage to the astronomer Carl Sagan. Dorion Sagan is also co-author of many of the books in which Margulis set out her scientific ideas. Interested in making science accessible to everyone, she published a wealth of educational material, as well as several books and videos for the general public.
She made her theories known all over the world through conferences and seminars and was satisfied to be considered, above all, a teacher. She called a spade a spade, and therefore always questioned the language used when talking about biological or evolutionary phenomena: cooperation, competition, struggle... "These are words that may be suitable for basketball, the computer industry or financial companies, but when it comes to evolution, they paint with a brush that is too fat," wrote Margulis and Sagan in their book Capturing Genomes.
Passion for life
One may wonder whether great thinkers and scientists like Lynn Margulis, who were passionate about their work and with a thirst for knowledge, spend any of their hours of the day 'disconnecting' from science and their usual concerns. In the case of Margulis, the answer is yes, because she was undoubtedly very passionate about life and someone who, according to those who knew her, enjoyed everything. "She was very fond of swimming," recalls Juli Peretó. "If there was a swimming pool in the hotel where she was staying, or near it, she always asked if she could take a bath".
Besides, she liked to cook for a lot of people and listened to classical music. Ricard Guerrero, professor emeritus at the University of Barcelona and a great friend of Margulis, explains: "He loved to read. One of his favourite writers was Emilie Dickinson, he knew many of her poems by heart. Sometimes she would ask me to recite something in the middle of a seminar. It was impressive to do this for an audience that was listening to science." Margulis and Guerrero worked together on a translation of Lorca's poem The Unfaithful Marriage. "When she was young she started reading Lorca and didn't understand anything, in fact, she kept a book of his where you can see the pencil notes of the words she looked up in the dictionary. With The Unfaithful Married Woman we looked up the translations that were available and none of them convinced us, so we got down to business," explains Guerrero.
From all these anecdotes, one can sense the close relationship that Lynn Margulis had with our country, which she visited frequently and where she was very successful thanks to her impeccable Spanish, although with a curious mix of Latin and Spanish expressions since she learned the language during a stay in Mexico.
"Lynn was undoubtedly the most interesting person I have ever met, and in my opinion, the most important microbiologist of the 21st century," says Ricard Guerrero. "With our team she learned about the great advances in bacteriology, together we observed many new microorganisms and especially the relationships between them". It was in the Ebro Margulis Delta that he and his colleagues isolated a giant spirochete (Spirosymplokos deltaiberi) that is viviparous and lives in environments without oxygen, a species with which he intended to better document his ideas about the endosymbial origin of cilia and scourges, a theory that he nevertheless died without being able to clearly demonstrate.
On the other hand, although the hypothesis of symbiosis seems much more reasonable than that of gradual evolution to explain the jump to the eukaryotic cell, there are still many unknowns. Javier Sampedro, in his book Deconstructing Darwin, explains some of them. For example, 347 genes have been found that are shared by all eukaryotic cells and that have not been observed, so far, in any prokaryote. Moreover, these genes are related to three cellular mechanisms exclusive to nucleated cells: endocytosis, the signal transduction system by which cells communicate with the outside world, and the whole complex of nuclear mechanisms that deal with processes related to the activation of genetic material.
A mystery that some scientists have tried to explain, in the purest Margulian style, with a new bacterial fusion: the chronocyte would be a protist that joined the feast of endosymbiosis by providing the 347 missing genes. The problem is that, until now, nobody has found the famous chronocyte.
The mysteries of evolution do not end with the origin of eukaryotes. There are numerous enigmas that take away the sleep of those men and women who devote all their efforts to answer the classic question "Where do we come from? Lynn Margulis, who went to her laboratory until the end of her days, was one of these people. The standard-bearer of that fascinating microbial world that she showed us in her books and lectures brought much light into that mysterious tunnel of questions that is the origin of our existence and of life itself.
As she wrote in the prologue to Capturing Genomes: "The entire evolutionary saga of how species originated and became extinct may constitute the greatest narrative ever told. After all, it is the story of each and every one of us.