The Tangled Tree

by David Quammen

  From the University of Wisconsin, with a master’s degree, she followed Carl Sagan to the University of California at Berkeley, where he had a postdoctoral fellowship. Their second son, Jeremy, was born in 1960. While her husband studied the possibilities of extraterrestrial biology (soon to be known as exobiology, the same discipline that helped get Carl Woese funded by NASA), she started on a doctorate in genetics, working around or somehow beyond the demands of mothering. “I was interested in evolution,” she wrote later, “and I always thought genetics was the way to study evolution in a deep way.” Lynn wanted to explore the phenomenon of non-Mendelian genetics, aka cytoplasmic inheritance, as she had learned of it from Ris and others at Wisconsin. She felt enticed by its implication: that genes are afloat in the cytoplasm of complex cells, not just bound up in the chromosomes within their nuclei, and that those genes could be very different from the nuclear genes. If so, where had they come from?

  But her advising professor disapproved of the topic. His disapproval was grounded within a broader problem that rankled her: the intellectual disjunction between scientific disciplines. “At Berkeley,” she recalled, “there was absolutely no relationship between members of the department of paleontology, where evolution was studied, and those of the department of genetics, where evolution was barely mentioned.” She called it “academic apartheid.” The geneticists on her side of campus had mostly begun as chemists, progressed into biology only so far as studying bacteria and viruses, and knew little or nothing about her great interest, cytoplasmic inheritance in eukaryotic creatures. They were so arrogant and ignorant, these Berkeley geneticists, that “they did not even know they did not know.” There she was, a twenty-three-year-old woman, with two young sons, and only a master’s degree plus her boundless self-confidence to set against them. Lynn knew she needed the doctorate so, in lieu of delving into evolutionary genetics, she produced a safer and smaller dissertation on the pond-water microbe Euglena gracilis. If I quoted you its title, your eyes would glaze like a Krispy Kreme doughnut.

  That was only a temporary setback for such a determined young woman. She was still busy at Berkeley in 1962 when the Ris and Plaut paper appeared, offering evidence of DNA in the chloroplasts of green algae. DNA in the chloroplasts meant cytoplasmic inheritance—genes passing down through a lineage of eukaryotic cells, complex organisms, independent of any role for fatherhood or the chromosomes. Her fascination with cytoplasmic inheritance grew, despite the discouragement of her dissertation advisor. She read into it more deeply, including a classic old book by the cell biologist E. B. Wilson, The Cell in Development and Heredity, in its 1925 edition, which mentioned still earlier works by Merezhkowsky and Wallin, both of whom had suggested that cell organelles such as mitochondria and chloroplasts were the evolved remnants of captured bacteria. Wilson called Merezhkowsky’s proposal “an entertaining fantasy,” dismissed Wallin somewhat more gently, and remained cautious on the subject himself, while admitting: “To many, no doubt, such speculations may appear too fantastic for present mention in polite biological society; nevertheless it is within the range of possibility that they may some day call for more serious consideration.” Lynn Sagan figured that day had come.

  Meanwhile, her marriage to Carl Sagan was foundering. Later, she would call Sagan “unbelievably self-centered,” a neglectful father, and a husband more needy of adoration than she could bear. The marriage, she would say, was like “a torture chamber shared with children.” She took the boys and left, moving into a place north of Berkeley with another young mother. But in 1963, when Carl Sagan accepted an assistant professorship at Harvard, she agreed to bring the boys and join him in an apartment west of Cambridge. Although he seems to have hoped they could save the marriage, to her it was “a move of convenience” with some ulterior motivation. Her doctorate hadn’t yet been granted, but she could settle that at a distance. She was through with California, disinclined to return to Chicago, and she thought Massachusetts might work out. It did, but not with Sagan.

  She divorced him in 1964. During this difficult period, working one job as a staff member with an educational services company, another as a lecturer at Brandeis University, raising two kids, and with modest financial help from her father, she found time to gather a vast array of facts, ideas, and references on endosymbiosis. She wrote her long paper on the subject, submitted it to a series of journals, and saw it rejected by those “fifteen or so” before the Journal of Theoretical Biology finally accepted it. She remarried, this time to Thomas N. (Nick) Margulis, a crystallographer, and took his surname. She got hired as an assistant professor at Boston University.

  Then, in 1969, pregnant with her third child (another son, Zachary) and obliged to stay home for extended periods, Lynn returned to endosymbiosis. “Enforced home leave permitted uninterrupted thought,” she wrote later. Her elder boys had started school. Her story of complex cells—that they had originated from the fusion of other life-forms, as encapsulated in the 1967 paper—now “sprouted, expanded, and eventually was pruned into a book-length manuscript.” Her recollection of “pruning” it to book length (329 pages, as published, not counting the index) reflects the fact that she was never shy, slow, or laconic about putting words on paper. She had a contract with Academic Press in New York. “I typed late into many nights, determined to make the deadline.” Finally, she boxed up the manuscript and the many illustrations she had commissioned for it, and mailed it all off to the publisher. This would represent a moment of triumph, and the beginning of tense expectation, for any writer. She waited. Five months later, the box came back, by the cheap rate for printed matter, without explanation. The peer reviews from other scientists had been bad, but at first Academic Press didn’t give her even the courtesy of hearing that. Eventually she got a form letter of rejection.

  Lynn went back to work, revising the manuscript and offering it elsewhere. This time it found appreciation and good editing at Yale University Press, by which it was published in 1970 under the title Origin of Eukaryotic Cells. She had dropped that bit about “On the Origin . . . ,” as she had used it for the 1967 paper, which was a wise and modest move, making the book title less closely an echo of Darwin’s. Still, her book too was a landmark, if not a classic. For many scientists interested in cell biology and deep evolutionary history, Origin of Eukaryotic Cells was the work that introduced the ideas of endosymbiosis and the name Lynn Margulis. Some of them thought she was nuts and some didn’t.

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  Lynn Margulis wasn’t the first to propose these unorthodox ideas, nor was Hans Ris. As she had learned at least passingly from reading E. B. Wilson’s old book, speculations about swallowed bacteria as the ancestors of cell organelles, about all complex cells having originated from combinations of simpler organisms, had been voiced for almost a century, though not always in “polite biological society.” One of those voices, not the first, not the steadiest, but with a timbre all its own, belonged to that Russian mentioned by Wilson and cited by Ris: Constantin Sergeevich Merezhkowsky.

  Merezhkowsky was born in 1855, in Warsaw, which was then part of the Romanov Empire. His father was a court official and a hidebound conservative, and Constantin, as eldest son among nine siblings, probably faced the first, fullest barricades of parental expectations. He went through a period of student radicalism, sympathetic with Russian revolutionaries opposing the tsar (whom they would assassinate in 1881), and defied his father’s wishes about a pragmatic career track, choosing to study natural sciences rather than law. During his student years at the University of St. Petersburg, Merezhkowsky joined a summer expedition to the White Sea and got interested in marine invertebrate animals, including amorphous creatures such as polyps and sponges. At age twenty-two, he published a paper on protozoans (a loose group of single-celled eukaryotes, including amoebae). More field trips, ranging as far as the Bay of Naples, gave him more opportunities to study protoplasmic gobs of life that had gotten little attention, and at one point he identified what he thought
was a new species of sponge. It’s hard to imagine the crusty father back in Warsaw sharing much excitement at that discovery. In any case, Merezhkowsky was wrong. His sponge turned out to be another protozoan, but bigger.

  He graduated in 1880, traveled through Germany and France for a few years, then returned to St. Petersburg and qualified as a privatdozent, a sort of freelance lecturer within the ambit of the university. He married a woman named Olga, and, after three years, they decamped to Crimea, which was then also part of the empire. On the southern coast of the Crimean peninsula, beyond the mountains, he worked as a pomologist—a fruit wrangler—supervising orchards. These facts come from a biographical study by a team of three scholars, including the excellent Jan Sapp; but where Merezhkowsky had picked up pomology skills, even Sapp and his colleagues don’t say. They do note: “Merezhkowsky’s career was unsettled between 1880 and 1902.” From age twenty-five to forty-seven, in other words, he knocked around, investigating this and that, here and there, and paying the bills God knows how. He did research on grapes. He studied the physical development of children, an odd digression for an invertebrate zoologist, and he described a method of measuring their bodies. That could have been innocent but looks creepy in light of later events. In 1898 he suddenly left Crimea, without Olga, without their son, Boris, and perhaps incognito, moving one jump ahead of local outrage. He stood accused of child molestation.

  The next place Merezhkowsky landed was California, traveling under a false passport as “William Adler.” He must have spoken with a strong Russian accent (though he wrote English well, as judged by the sponge-discovery paper, which had been published in London), and presumably the name William Adler was a poor fit—but this was California in the Gilded Age, and he wouldn’t have been the only pilgrim reinventing himself. While on the lam, he wrote a fantastical novel, The Earthly Paradise, ramblingly subtitled A Winter Night’s Dream. A Fairytale of the Twenty-seventh Century: A Utopia, which was later published in German for lighthearted souls to enjoy. I suppose it bears saying that no, I’m not making this stuff up. Nor did Jan Sapp concoct or hallucinate it; one of his coauthors, Mikhail Zolotonosov, researched Merezhkowsky’s later pedophilia case in seventy Russian newspapers and secret files of the police.

  As the century turned, Merezhkowsky spent time at a research station on the coast south of Los Angeles, then at Berkeley, continuing his work on marine life when he wasn’t writing fantasy fiction. He focused now on diatoms, a kind of single-celled alga with each cell enclosed in a shell-like silica wall. Diatoms are extraordinary; minuscule beings aren’t supposed to seem so intricately and geometrically neat. Many of them contain chloroplasts, meaning they live by photosynthesis, like plants. Although their external walls show a great range of diversity, decorative and useful for classification, Merezhkowsky began reclassifying them by their internal anatomy, including the chloroplasts. Dwelling on those chloroplasts, which through a microscope looked very much like bacteria, may have led him toward the big idea of his life: that internalized bacteria had become chloroplasts, not just in photosynthesizing algae but also in plants. He eventually named this phenomenon symbiogenesis, defined by him as “the origin of organisms by the combination or by the association of two or several beings which enter into symbiosis.”

  The simpler word symbiosis had an earlier history of its own, originally as applied to a community of people. Its biological usage dates back to a German biologist, Anton de Bary, in 1879, for whom it meant any sort of merger or close cohabitation by two or more different forms of life. The term encompassed relationships ranging from parasitism, to temporary partnership (with one or both partners deriving benefit), to intimate and heritable integration of the sort that Merezhkowsky would later propose. De Bary himself recognized that a lichen, for instance, represents not one creature but a symbiotic association between at least two kinds: algae or cyanobacteria living amid fungi. A clown fish, feeding blithely on parasites amid the stinging tentacles of a sea anemone, is engaged in symbiosis. But the idea that one organism could exist permanently inside the cells of another, replicating itself as the cells replicate themselves and becoming part of a new, composite, and heritable identity, was taking the idea a step further: symbiogenesis.

  Several researchers of the late nineteenth century had considered that possibility in connection with chloroplasts, including de Bary’s student Andreas Schimper, an adventurous German botanist from a family of eminent scientists, who traveled widely during his early manhood for fieldwork in the West Indies, South America, Africa, and the Indian Ocean. Schimper grew up in that French borderland city, Strasbourg, where the Rhine River divides Germany from Alsace. One photo shows him looking youthful, earnest, and wide-eyed, weighted down with a large handlebar mustache as though he had pasted it on for a school play. During the mid-1880s, not yet thirty years old, he published two memorable papers, in one of which he coined the term chloroplast and mused that, if these things reproduced themselves within plant cells rather than arising anew from plant cytoplasm, the compound entity “would be somewhat reminiscent of a symbiosis.” Just an analogy, just an aside, which Schimper didn’t pursue further, partly because it seemed too bizarre to be taken literally, and maybe also because he died early, age forty-five, from ruined health after an expedition to malarial regions of Cameroon.

  Merezhkowsky read one of Schimper’s papers, and, lo, the idea of symbiogenesis came to him in what he called “a completely spontaneous way.” In 1902 he returned to Russia, but not to Crimea, where memories of his alleged or real turpitude might have made him unwelcome or, worse, wanted. Instead he found a position at Kazan University, five hundred miles east of Moscow on the Volga River. He became a privatdozent again. Three years later, he published a paper, in German, like Schimper, on the origin of chloroplasts in plants, enunciating the symbiotic theory. That was his famous work of 1905, in which he identified cyanobacteria (he called them cyanophytes) as the strangers that came to stay. In a series of further papers over the following fifteen years, he expanded on the theory, gave it that name (symbiogenesis), and claimed it as uniquely his. Never mind poor Schimper, long gone. In truth, according to Jan Sapp and others, Merezhkowsky did more than anyone else to promote this partial version of the bigger idea—that chloroplasts, at least, are captured bacteria within composite organisms called plants—until the rise of Lynn Margulis.

  The accepted view of how plants came to be plants, Merezhkowsky wrote in the 1905 paper, with a tinge of derision, was that chloroplasts were simply innate “organs” of each cell, which had “gradually differentiated” out of the otherwise colorless cytoplasm. That was the endogenous theory: chloroplasts had taken shape on the inside of plant cells, formed from internal materials. Not so, he argued. Rather than being homegrown organs, they are “foreign bodies, foreign organisms” that invaded the cytoplasm of animal cells sometime in the distant past and entered into a symbiotic coexistence. According to this theory, a plant cell is nothing but an animal cell with photosynthetic bacteria added. The plant kingdom derived from the animal kingdom by symbiogenesis. It had happened several times, in several independent events of conjunction, according to him—maybe as many as fifteen, giving the plant kingdom that many separate origins. How the animal kingdom originated was another question, which he mostly ignored.

  After ten pages of close argument, Merezhkowsky ended with an evocative passage that has become famous to those who read the literature on cell origins, and that has remained unknown, incomprehensible, to everyone else:

  Let us imagine a palm tree, growing peacefully near a spring, and a lion, hiding in the brush nearby, all of its muscles taut, with bloodthirsty eyes, prepared to jump upon an antelope and to strangle it. The symbiotic theory, and it alone, lays bare the deepest mysteries of this scene, unravels and illuminates the fundamental principle that could bring forth two such utterly different entities as a palm tree and a lion.

  How does symbiogenesis explain the palm tree and the lion? Well, the tree be
haves peacefully because it contains all those pacific little workers—those docile “green slaves,” the chloroplasts—nourishing it from sunshine. The lion needs meat. So it kills. But wait: imagine each cell of the lion filled with chloroplasts, Merezhkowsky suggested. They would generate sustenance for the lion from solar energy. Thus equipped, “I have no doubt that it would immediately lie down peacefully next to the palm, feeling full, or needing at most some water with mineral salts.”

  That would be sufficient diet for his green lion: sunbathing and Gatorade.

  A nice idea, but he was wrong. As several alert biochemists from our own time have noted, a lion has vastly less surface area than a plant of equivalent mass (think about all those spreading palm fronds or the canopy of an oak), so that spackling its skin with chloroplasts, like a chartreuse sequined suit on Liberace, wouldn’t catch nearly enough sunlight to power a robustly leonine life. The energy input would be insufficient. The lion would wind down to a torpid, immobile groan, weak as an Energizer Bunny with bad batteries.

  These papers on symbiogenesis didn’t bring Merezhkowsky either scientific eminence or peaceful repose. He was a lion without meat, without even chlorophyll, hungry and mean. He shifted his politics from left to right, and during the Kazan years, he became an informer to the tsar’s oppressive, anti-Semitic secret police. He denounced a Jewish colleague who was up for promotion. He seems to have continued “measuring” children. He absconded from Russia the second time in 1914, with charges swirling behind him that he had raped twenty-six little girls, including at least one he had tutored. Criminal cases were opened in Kazan and St. Petersburg. The charges never came to trial, so they are only accusations, not damnations, but presumably there was some basis. He went to France and continued writing, not just papers on symbiogenesis but also another dizzy philosophical book with science-fiction trappings, featuring a “seven-dimension oscillating universe,” spiritualism, atheism, and eugenics, as well as cosmic evolutionary theory; then, in his final year, a short manuscript of “Instructions for My Disciples,” offering himself as savior of the world. He was the L. Ron Hubbard of his day, crazed and megalomaniacal, but without the successful marketing or the celebrity followers. Not even Mikhail Zolotonosov, Jan Sapp’s deep-burrowing Russian coresearcher, seems to know what became of Olga and Boris. By the time Merezhkowsky produced his last scientific article, “The Plant as a Symbiotic Complex,” published in French in 1920, he was burning down to the end of the wick.