Haeckel was a fervent young man, prone to deep intellectual, aesthetic, and emotional excitements, a German Romantic in the tradition of Schiller and Goethe. His turn to marine biology began during a summer getaway from his medical studies in 1854, when he and a friend caught a boat from Hamburg to one of the islands of Heligoland, a small archipelago fortysome miles offshore in the North Sea. It started as a lark but became a formative experience for Haeckel when they fell in with Johannes Müller, a renowned zoologist from Berlin, who was there to study starfish, sea urchins, and other echinoderms. Scooping up invertebrate animals from the sea and examining them with this scientist was revelatory. Müller’s friendship and guidance swung Haeckel from botany to marine zoology, with special attention to invertebrates. Back in Berlin, Müller’s journal published Haeckel’s first zoological research article while he was still a medical student. The mentorship might have continued, but in April 1858 Müller died of an opium overdose—probably a suicide, provoked by depression, Haeckel suspected.
That spring was a dark and confusing time for Haeckel. He was twenty-four, quitting medicine for a scientific career, and now his best teacher had jumped into an early grave. The turmoil gives some context for what happened next: two days after Müller’s funeral, Haeckel became engaged to a young woman named Anna Sethe. He had known her almost six years, and she was his first cousin, daughter of his mother’s brother. Haeckel’s own brother had married Anna’s sister; it was at their wedding that he had met Anna, whom he saw as a dancing seventeen-year-old “elf.” This sort of tangled intermarriage within families wasn’t rare or titillating in nineteenth-century middle-class circles: Charles Darwin himself married his first cousin, Emma Wedgwood, and Darwin’s sister Caroline married Emma’s brother Josiah Wedgwood III. But despite the cozy family linkage, Haeckel (unlike Darwin, who could never be mistaken for a German Romantic) embraced his chosen partner with a great passion. Anna to him was a “true German child of the forest, with blue eyes and blond hair and a lively natural intelligence,” and a soulmate with whom he looked forward to sharing “every thought and every action.” In a letter that summer, he told her: “When I press through from this gloomy, hopeless realm of reason to the light of hope and belief—which remains yet a puzzle to me—it will only be through your love, my best, only Anna.” Unfortunately, he couldn’t marry her yet because he didn’t have a job.
Haeckel’s other great passion was science. Rather than turning back toward medicine for a livelihood that might have supported marriage, he launched himself toward marine zoology as a sort of freelancer, again with more heart than practicality. He gathered up some equipment and, in early 1859, went to Italy. After seeing Florence and Rome as a tourist, and disliking the tedious religious flavor of the art, he tried Naples for its access to the sea. That didn’t work out so well either. He was living in crummy digs, annoyed by the Neapolitans, losing his religious faith, and frustrated at the work, trying to do zoology from the buckets of bycatch he got from fishermen on the waterfront. After almost six months there, Haeckel felt he was getting nowhere. So he crossed the Gulf of Naples to Ischia—another island but now a Mediterranean one, warmer and more picturesque than Heligoland—taking a palette and easel to do some painting. His luck in travel encounters was good, and this time he met Hermann Allmers, a German poet who was also a painter. Allmers was a small man, older, with a formidably hooked nose and a thrust chin—a strange match to Haeckel, who was tall and handsome, long-faced, with curly blond hair, a beard, and presumably by now bronzed from the Mediterranean sun. But their interests, talents, and dispositions meshed well, and after a week of knocking around the island, they were fast friends.
From Ischia they went to Capri, where they swam, painted, and danced (Haeckel did, anyway) the tarantella. It was just what a troubled twenty-five-year-old should be doing, that sort of spirit-cleansing interlude, but it wasn’t getting Haeckel any closer to marrying Anna. After a month on Capri, he and Allmers went to Messina, on Sicily—which was not just another island but a turn back toward science for Haeckel, because in this very place, Johannes Müller had done fieldwork. After five more weeks of cavorting and painting, crisscrossing Sicily, climbing Mount Etna, Allmers had to leave, and Haeckel got serious about zoology. The landscape of Sicily he found boring and threadbare, but the sea was full of abundance and variety. Based on what came from the water, Haeckel called Messina “the Eldorado of zoology.”
He was still torn between art and science, and between his romantic vision of an artist’s rich experience, on the one hand, and an academic scientist’s salary, which would allow him to marry. He was overwhelmed by the diversity of sea creatures he was seeing and trying to study. At the end of November 1859, according to Robert J. Richards, “with just a few months left for his research in Italy, Haeckel finally decided to focus on just one group of animals, the almost unknown radiolaria.” They aren’t actually animals, the radiolarians, they’re something else, but never mind; that fact was unknown and unimportant to Haeckel at the time.
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Ernst Haeckel found a boggling diversity of these tiny, glassy creatures in his sea-water samplings at Messina, and, within a few months, he’d shipped home specimens representing more than a hundred species previously unknown to science. His revered teacher Müller had led him to the topic by way of a short monograph on the radiolaria that Müller published shortly before killing himself, and which Haeckel carried with him to Italy. He depended heavily on that guide as he got started. But he quickly went beyond Müller, not just discovering new species but also drawing the creatures in microscopic detail, beginning to scrutinize their soft internal anatomy as well as their external silica skeletons, and trying to classify them in some orderly way. Back in Germany after the Italian rambles, Haeckel got permission to work on his harvest at the Berlin Zoological Museum, and he started writing a report. Around the same time, in the summer of 1860, one other factor added to his focus and momentum: he read the German edition of On the Origin of Species and fell in love with Darwin’s theory.
His report on the radiolaria grew into a dissertation, and the dissertation would soon grow into Haeckel’s large, two-volume, lavishly illustrated monograph. But he still couldn’t afford to marry Anna, or felt that he couldn’t, so he interrupted the radiolarian effort to accept paid work. A friend on the medical faculty at the University of Jena, southwest of Berlin, offered him an assistant’s position, which might lead to something more. Jena was a special place, considered the cradle of German Romanticism, site of a distinguished university, rich in cultural ferment as well as intellection—suffused with the spirits of Schiller and other philosophers and poets, and just down the road from Weimar, where Goethe lived. About the offered job, Richards tell us: “He had no choice. Jena, that warmhearted and energetic pulse of Romantic élan, could not be refused, especially since its embrace might also bring him into the arms of that other love, Anna.” Haeckel took the assistantship and qualified as a privatdozent at the university. Working hard, burning long hours, he did his teaching and also finished Die Radiolarien, both volumes, and had them printed in Berlin. On the strength of that book, extraordinary coming from an unknown junior scholar—extraordinary coming from anyone—he was offered a professorship at a good salary and directorship of Jena’s Zoological Museum.
That summer, back in Berlin, Haeckel married Anna. She shared his love of nature and art, understood something of his intellectual passions, and called him “her German Darwin-man.” Their happiness would last eighteen months.
His new status at Jena was gratifying, but it didn’t make him famous. His transition from obscure young zoologist to prominent explicator of Charles Darwin’s theory happened suddenly with a public triumph at the thirty-eighth meeting of the Society of German Natural Scientists and Physicians, a large scientific organization, on September 19, 1863. That year’s gathering was in the Prussian town of Stettin. Haeckel was invited to give the big opening lecture.
Before an au
dience of two thousand people, society members and guests, to whom the topic had been advertised, he spoke for an hour about evolution by natural selection. Haeckel noted that earlier thinkers had floated evolutionary ideas but that no one before Darwin had offered a material theory, involving laws of inheritance and variation. He described the mechanisms of selection and adaptation. He cited three kinds of evidence supporting Darwin’s big idea: the fossil record, the clues inherent in embryology, and the patterns of relatedness suggested in systematic classification. Relatedness implied divergence from common ancestors. “The whole natural system of plants and animals,” Haeckel said, “appears from this perspective as a great stem tree, and so each genealogical table of relations can be represented intuitively in the form of a ramifying tree whose simple roots lie hidden in the past.”
Stammbaum was his word, a stem tree, a family tree, upon which every branch and twig represented a form of life evolved by natural selection from some other form of life—every form except, possibly, the very first and simplest. (He was still undecided, or anyway ambiguous in public, about whether life began from an act of God or a chemical accident. Later, he would opt for the latter.) And he made explicit what Darwin had hinted in The Origin: that this evolutionary process, this tree, included humans.
Just how the tree should be drawn was another question, which Haeckel would address soon enough. For the moment, he enjoyed the great applause of his audience and the extensive coverage next day in a local newspaper, Stettiner Zeitung, a clipping of which he sent proudly to Darwin just a few days after Darwin had thanked him for the gift of the books.
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This phase of Haeckel’s life, beginning from the splash at Stettin, was glorious but brief. Back in Jena with Anna, he taught a very popular lecture series on Darwin’s theory, illustrated with large drawings by his own hand. One student remembered decades later how Haeckel would stride into the auditorium with “the victorious rush of an Apollonian youth.” He was slender, looked thoughtful but dashing, with “great golden locks flowing from his large head, which itself evinced a great brain.” His large blue eyes were “blazing yet friendly—he was probably the most handsome man I had ever seen up to that time,” the dazzled student testified. The lectures he poured out were as brilliant as his appearance. Off the podium, Haeckel continued his study of Darwin’s theory and its application to real groups of organisms, including the radiolarians. In late January of the new year, 1864, his life turned dark.
Anna fell sick with what Richards reports as pleurisy, a lung-related inflammation. She improved, then she relapsed, or suffered something new, this time with abdominal pains suggesting appendicitis. Haeckel himself later called it typhoid fever. By an alternate account, she had a miscarriage with fatal complications, and the details were concealed from her husband. Whatever her trouble, on the night of February 15, the agonies came to a peak, and she lost consciousness the next morning. February 16 was a bizarre day for Haeckel, bringing a gruesome mix of events: he got word that he would receive a prestigious award, the Cothenius Medal, for his scientific work; he turned thirty years old; and that afternoon, Anna died.
The central theme of the Richards biography is that Anna’s death was the defining moment in Haeckel’s life, killing whatever remained of his religious faith, his sense that there existed a spiritual dimension apart from the material dimension, and turning him to Darwinian theory as a kind of substitute theology. Going beyond even Darwin (who underwent his own loss of faith, catalyzed partly by the death of his favorite daughter), Haeckel replaced God with natural selection, as the central force in what he called his “religion of monism.” What he meant by monism was a bit paradoxical and woozy: God is nature, nature is God, mind and matter are two manifestations of some single underlying reality, neither can exist without the other, and therefore (by implication) immortal souls and eternal rewards don’t exist. Haeckel called this “the purest kind of monotheism,” but Judeo-Christian theologians wouldn’t agree. For orthodox believers of Haeckel’s day, Richards writes, monistic metaphysics “could only be viewed as transparently shrouded atheism.” Whatever Haeckel’s monism was, ineffable or just dreamy, it guided his version of Darwinian theory—as he promulgated that theory (or anyway, that version) in his writings and lectures over the next fifty-five years.
More important to us, though, is how he promulgated that theory in his art: by drawing evolutionary trees of life that portrayed actual creatures and their actual patterns of descent and divergence, not just letters and dots in a hypothetical figure. He made phylogenetics concrete.
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Haeckel’s first response to Anna’s death was prostrate grief. He spent eight days in bed, half delirious. When that passed, his parents sent him to Nice, France, for a convalescent getaway. While walking along the seashore, he caught sight of a beautiful jellyfish in a tide pool and watched it for hours, its long tentacles reminding him of Anna’s golden hair flowing out below a headband. Seeing his dead wife in the shape of a jellyfish sounds a little ghoulish, but it helped reconnect Haeckel with his passion for nature and science, his efforts now rededicated to her memory. The jellyfish represented a new species, and he named it Mitrocoma annae, meaning “Anna’s headband.”
His second response to her death was work. He buried himself in a new writing project: an ambitious book synthesizing his views of Darwinian theory, monism, and a whole edifice of “natural laws” discovered by him, framed in new terminology invented by him. Darwin’s natural selection was his primary law, but he had no shyness about adding Haeckelian corollaries. He offered “laws” of inheritance and “laws” of adaptation. There was a law of uninterrupted or continuous transmission and a law of interrupted or latent transmission. There was a law of correlative adaptation. There were many others in that vein—more than 140, according to Richards, who describes this new book as “stuffed with as many lawlike proposals as the municipal code of a small city.” The neologisms with which Haeckel salted it have been more useful and durable than his laws. He coined the term ecology. He coined the term phylogeny. He coined the term ontogeny and propounded what he called the biogenetic law, asserting that the embryological development of an individual retraces the course of its evolutionary descent. A human embryo, by this argument, passes through stages at which it looks like the embryo of a fish, then of a salamander, then of a rabbit. Put in three words, as it would later be famously known: ontogeny recapitulates phylogeny.
Haeckel wrote the opus, two volumes again, a thousand pages, with illustrations, in a year of ferocious effort. “I lived then quite like a hermit, allowed myself barely 3–4 hours sleep daily, and worked all day and half the night,” he said afterward. The work appeared in 1866 as Generelle Morphologie der Organismen, a study of the shapes of living creatures—including the origins of those shapes. According to Richards: “It contains the foundation for all of Haeckel’s later thought.” It also contains an arresting series of trees. He drew them in ways no one else had: as an artist-scientist, illuminating evolution with flair.
The idea of drawing evolutionary trees may have been planted in Haeckel’s imagination by Darwin’s diagram in The Origin, which was artless but important. Or it might have come from two other sources, one or both: Heinrich Georg Bronn, a paleontologist who translated Darwin’s book into German, or Haeckel’s friend August Schleicher, a linguist. Bronn had published an essay in 1858 on the laws of development of living creatures, and that essay included a sort of stick-figure rendition of a tree. It was another bare abstraction, a naked sketch, suggesting the idea of progressive lineages but without committing to specifics. Bronn himself was no evolutionist at that point, one year before Darwin’s book appeared in English, and Bronn attributed his progression of forms to a “creative force,” not natural transmutation. So his tree was an old-school tree. Still, Haeckel may have seen it and envisioned a new meaning. Haeckel’s other possible inspiration was a book by Schleicher presenting what its author called a “Darwinian” theor
y of linguistic evolution, in which the divergence of languages, ancient to modern, was depicted in a branching diagram. Influenced or not, Haeckel seized on the tree shape and went far beyond Darwin, far beyond Bronn or anyone else, in drawing evolutionary trees. He bundled eight of them into his Generelle Morphologie, covering eight major categories of living things.
And his were different, as I’ve said: specific, not hypothetical. The limbs and branches of these trees fruited with the names of actual creatures and groups of creatures, not vague letters. Each tree offered a concrete proposal about which animals, plants, or other life-forms share ancestors with which others. Some of them also presented phylogenies (histories of ancestral lineages), putting that new word of his to good use. Not least important, his trees were visually rich and deftly executed, displaying Haeckel’s graphic talent and his maniacal attention to detail. The most intricate of them, his Stammbaum der Wirbelthiere, a Family Tree of Vertebrates, has so many long, slender branches, rising vertically but pulled a bit sideways, that it looks more like a great clump of seaweed swaying gently in the current than like a rigid maple or elm. Nobody had ever drawn a tree of life like Haeckel’s trees.
His vertebrates tree included mammals, reptiles, amphibians, fish, and birds, of course, with a vertical axis along the left border showing increments of geological time, throughout which these classes had arisen. There was a Family Tree of Coelenterates, within which grew the jellyfishes, now his sentimental favorites, among many other forms. There was a Family Tree of Mollusks, a Family Tree of Plant Kingdoms, and a Family Tree of Articulate Animals, which contained arthropods and worms. Mammalian forms, besides being placed on the vertebrates tree, got another tree of their own, his Stammbaum der Säugethiere (Family Tree of Mammals), and in its upper-right-hand corner, you can see a small branch denoted “Homo sapiens,” just beside an equally small branch for gorillas. That branching implied: we are another ape.
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