The Tangled Tree: A Radical New History of Life

But they weren’t connected, in Augier’s mind, by descent from shared ancestors. Despite the hint he gave to himself in his language about family trees—all branches divergent from “the stem to which they owe their origin”—there is no evidence in Augier’s writing or his tree figure that he had embraced, or even imagined, the idea of evolution.

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That idea was coming soon, and, with its arrival, the tree of life would change meaning. The change was drastic, soul shaking to many people who lived through it, because it reflected a challenge to faith, and it met strong resistance. Jean-Baptiste Lamarck, France’s great early evolutionist, and Edward Hitchcock, an American who prided himself a “Christian geologist,” are the two scientists whose works—and whose graphic illustrations—best reflect how tree thinking shifted during the decades before Darwin unveiled his theory of evolution.

Lamarck was a protean figure: a soldier from a family of soldiering minor nobility who transformed himself into a botanist, then into a professor of zoology at the Muséum National d’Histoire Naturelle in Paris, to which he was appointed in 1793, on the eve of the Reign of Terror. His title at the museum put him in charge “of insects, of worms, and microscopic animals,” three categories of life he had never studied, but he adapted fast, and even invented the word invertebrates to cover them. He abandoned plants and studied his invertebrates through the grimmest days of the French Revolution, earning a measly salary but at least keeping his head, as other scientists such as Antoine-Laurent Lavoisier went to the guillotine. Lamarck had probably helped his standing among the revolutionaries back in 1790 while employed at what was then the Jardin du Roi, when he urged dropping the royal label and renaming that institution the Jardin des Plantes. Clearly, he had good political instincts. He held the conventional view of species—that they were fixed forever and created by God—until 1797, but then his views changed, possibly as a result of his study of fossil and living mollusks, which seemed to show patterns of gradual transformation. He came out as an evolutionist on May 11, 1800, in his first lecture for the year’s course on invertebrates. After that, he published three major works on evolutionary zoology, the most influential being his Philosophie Zoologique in 1809.

Lamarck outlived four wives and three of his seven children, living beyond the revolution, through the Napoleonic era and most of the Bourbon Restoration, a handsome man with a downturned mouth, balding slowly across his pate, blind for his final ten years, his faithful daughter, Cornelie, giving her life to him and reading him French novels. He died at eighty-five and was eulogized by important colleagues such as Geoffroy St. Hilaire, after which things didn’t go so well: his remains were interred at the Montparnasse Cemetery in a common trench, not a permanent individual plot, and because such burial trenches were regularly recycled, his bones may have ended up in the Paris catacombs, along with those of thousands of paupers and other neglected folk. There was no Lamarck grave to visit. He became, according to one biographer, rather quickly “forgotten and unknown.” His fame would return, if not immediately, but still it was a cold finish for the world’s first serious evolutionary theorist.

Lamarck nowadays is commonly associated with what his name came to represent: Lamarckism, an easy but imprecise label for the idea of the inheritance of acquired characteristics. Many people are vaguely aware of him as a predecessor to Darwin; he is seen as a forerunner whose theory was provocative but wrong, refuted by later evidence because it depended, as Darwin’s did not, on that illusory notion of acquired traits being heritable. (The real facts aren’t so simple. For instance, Darwin himself included the inheritance of acquired characteristics as a force in evolution, under the label “use and disuse.”) The most familiar example of such inherited adjustments, which Lamarck himself offered, is the giraffe. The proto-giraffe on the dry plains of Africa stretches to reach high foliage, its neck lengthens (supposedly) from the effort, its front legs lengthen too, and therefore (again supposedly) its offspring are born with longer necks and front legs. Lamarckism, in that cartoonish form, has been easy to despise but harder to kill off entirely.

It came back into fashion during the late nineteenth century, when the general idea of evolution gained acceptance but the crucial details of Darwin’s particular theory, offering natural selection as the primary mechanism, were widely rejected. Natural selection just seemed too mechanistic, too stark and unguided, and many evolutionists found it unpalatable. This situation went on for decades—the world accepting Darwin’s idea of evolution but not his explanation of how it occurs—though only historians remember that now. Lamarckism became neo-Lamarckism and seemed a less nihilistic alternative. It has continued to linger as a dubious but ineradicable notion—embodied in that single tenet, the inheritance of acquired characteristics—enjoying small surges of reconsideration even down to the present day.

But that single tenet was never Lamarck in totality. He had other ideas, some even worse. He believed in spontaneous generation. He disbelieved in extinction, at least as a natural process. He argued that “subtle fluids,” surging through the bodies of living creatures, helped reshape them adaptively.

In one of his earlier botanical works, before the shift to animals and the epiphany about evolution, Lamarck had arranged plants in what he called “the true order of gradation”: from least perfect and complete to most, ascending along an old-fashioned ladder of life. He matched that with a separate ladder for animals, a “counterpart” arrangement, showing an ascending series of forms: from worms, through insects, through fish and amphibians and birds, to mammals. Neither of those ladders hinted at divergence from common ancestors or transformation. But in the 1809 book Philosophie Zoologique, he included a different sort of figure, subtle yet dramatic, depicting animal diversity. It was a branched diagram, descending down the page, with major animal groups connected by dotted lines, like one of those connect-the-dots games for kids on the paper placemats at a pancake house. Connect the dots and discover that the secret shape is … an airplane! Or … an elephant! Or … George Washington’s head! In Lamarck’s dotted figure, the secret shape was a tree.

Lamarck’s tree of dots, 1809.

Birds sat perched on a branch divergent from reptiles. Insects had diverged from the main trunk before it yielded mollusks. Walruses and other marine mammals lay farther along that trunk, beyond which still other branches led to whales, then to hoofed mammals, and finally to all other mammals. Wrong though it was about the particulars, and despite being upside down, this figure marked an important transition in scientific thought. Scholars tell us that it was the earliest evolutionary tree.

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Edward Hitchcock stands as a counterpoint to Lamarck, with that first evolutionary tree, in that Hitchcock offered a last pre-evolutionary tree in the decades before Darwin changed everything. In fact, Hitchcock presented two separate trees of life, one for animals, one for plants, in his 1840 book Elementary Geology, which became a successful and often-reprinted text in the mid-nineteenth century. Hitchcock’s trees were also innovative—among the first based on deep knowledge of fossils, not just close observation of living creatures. He called his illustration a “Paleontological Chart,” and what it shows is diversification of the animal and plant kingdoms charted against geological time, from the Cambrian period (beginning about 540 million years ago) to the present.

Hitchcock’s trees weren’t classically tree shaped, spreading outward into a canopy like a maple or an oak. Each of the two, the one for animals and the one for plants, looks more like a windbreak of tightly placed Lombardy poplars grown to maturity along a roadway. The base of each windbreak is a thick, solid trunk from which rise slender stems, fluffy with foliage but without much branching as they ascend. Vertical, parallel, they seem independent: crustaceans, worms, bivalves, vertebrates. The vertebrate stem does branch into several shafts. The shaft leading up to modern mammals culminates in the word Man, atop which sits a regal crown adorned by a cross.

The crowned “Man,” with its cross, tells us what we need to know about Hitchcock’s sense of hierarchy in the living world. He grounded his geology firmly within the tradition known as natural theology, meaning science purposed to illuminate the power and wisdom of God as creator of all, with humans as the culmination of that divine creativity. He was a devout, driven New England Yankee, and his “Paleontological Chart” reflected his view of humans as the apogee of creation, as well as his findings in geology.

Hitchcock was born to a poor family in Deerfield, Massachusetts, his father a Revolutionary War veteran and a hatter by trade, with debts and three sons, who found just enough money to see his boys through primary school and some time at the local academy. After that, as Hitchcock recalled, “nothing was before me but a life of manual labor.” He balked at the idea of apprenticing as a hatter, to his father, or in any other trade. Instead he worked on a farm—it was rented land, cropped by one of his brothers—for a period that stretched on so long, or what felt like so long, that later he claimed not to remember how many years. With his free time, especially rainy days and evenings, young Edward studied science and the classics. Ambitious and hungry, he thought he was preparing himself for Harvard. Under the influence of an uncle, he took up astronomy. Then came the great comet of 1811, a celestial passerby that reached its peak of brightness in the north sky during autumn that year, when Hitchcock was eighteen. He borrowed some instruments from Deerfield Academy and spent night after night measuring its progress. “I gave myself to this labor so assiduously that my health failed,” he wrote later.

The health crisis brought on a religious conversion: from Unitarianism, into which he had drifted, back to the Congregationalism of his father. That passed for a drastic rethink in Edward Hitchcock’s life. In lieu of Harvard, he returned to Deerfield and somehow got hired, at age twenty-three, as principal of the academy. Then he studied for the ministry, was ordained, and became pastor of a Congregationalist church in Conway, Massachusetts, just up the road from Deerfield. Throughout these years and for the rest of his life, Hitchcock remained an invalid in self-image if not bodily, obsessed with his own fragility, continually complaining that he felt death nearby, although he lived to be seventy. One scholar, having looked into his life and work, called him “a hypochondriac of the first rank.”

Hitchcock’s “Paleontological Chart,” 1857 version.

Conveniently for his scientific career, he was “dismissed” from the Conway pastorate in autumn 1825 on the grounds of impaired health and imminent death if (according to his own worried judgment) he didn’t stop preaching, circuiting the parish, and running revivals. Amherst College, recently founded, hired him to teach chemistry and natural history, and he stayed there the rest of his life, serving later as professor of natural theology and geology, and for one nine-year stretch also as president. The early years of Hitchcock’s career at Amherst spanned the period when Charles Lyell, in England, published his multivolume Principles of Geology, a radical work that challenged Scripture-based interpretations of the geological record, including Hitchcock’s own.

The conventional school of thought, known as catastrophism, saw Earth’s history as a series of cataclysmic upheavals cast down like thunderbolts by the Creator, such as the bolt that brought forty days and forty nights of rain, documented in Genesis as Noah’s flood. These catastrophes were considered directional and purposeful, in the sense that God used them as occasions for purging the planet of some creatures (dinosaurs, begone) and adding new creations (mammals, arise). Lyell’s alternative view was uniformitarianism, insisting that the processes and events that shaped Earth in the past were physical, such as erosion and deposition, as well as the occasional volcanic eruption—things that continue to occur in the present at roughly the same rate they did in the past. Those forces caused extinctions, among other effects. Second thoughts by God about what fauna and flora should exist, according to Lyell, did not enter into it.

Hitchcock read Lyell’s work promptly as the first three volumes came out, from 1830 to 1833, and found it all discomforting. He was no young-earth creationist himself; he acknowledged that volcanism and erosion were continuing processes. But he worried that Lyell’s view of the planet would “exclude a Deity from its creation and government.” In an article on deluges, comparing the biblical with the geological records, Hitchcock wrote cattily: “We know nothing of Mr. Lyell’s religious creed. But there is something in such an ambiguous mode of treating of scriptural subjects that reminds us of infidel cunning and duplicity.” Lyell was a dutiful Anglican, not an infidel, at least when he authored Principles of Geology, but Hitchcock seems to have sensed, maybe better than Lyell himself, that his work would nudge some readers toward godless, materialistic ideas.

One of those so nudged was Charles Darwin, who read Lyell’s three volumes aboard the Beagle and followed their influence, not just toward uniformitarianism in geology but eventually (because Lyell described Lamarck’s ideas, without endorsing them) toward a theory of evolution. So although Hitchcock was wrong about Lyell’s supposed “cunning and duplicity,” he was right about Principles of Geology taking readers—one crucial reader, anyway—onto a slippery slope.

In 1840, seven years after Lyell’s third volume appeared, Hitchcock published his own Elementary Geology, and with it that Paleontological Chart of Lombardy poplars, included as a hand-colored, foldout figure presenting his two nonevolutionary trees of life. The chart showed changes in Earth’s flora and fauna over geological time, with this or that group of plants or animals waxing or waning in diversity and abundance, but not much branching of one from another. The cause of those changes, Hitchcock explained in his text, was God’s direct agency, adding and subtracting creatures, improving and perfecting the world as a long-term project. The major groups were present all along, according to this slightly tortured schema, but new species manifesting “a higher organization” had been inserted along the way, until at last Earth was ready for “more perfect” kinds of creatures, “the most generally perfect of all with man at their head.” The gradual introduction of “higher races,” he wrote, “is perfectly explained by the changing condition of the earth which being adapted for more perfect races Divine Wisdom introduced them.” These were special creations by the Deity, appropriate as environments changed. God wasn’t rethinking the planet’s fauna and flora, just adjusting them to newly available niches. If that doesn’t quite make sense, don’t blame Charles Lyell or me.

Hitchcock’s Elementary Geology was a hit. Between 1840 and the late 1850s, it went through thirty editions, to which he made minor revisions of language and data. Throughout all those editions, the trees figure remained—unchanged except for color adjustments. Then something happened. As a consequence of that something, or else by improbable coincidence, the thirty-first edition of Hitchcock’s book, in 1860, contained a notable difference. An omission. No trees.

What happened was that in 1859 Charles Darwin published On the Origin of Species. His book also contained a tree, but one with dangerous new meaning.

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By that point, Darwin had incubated his theory in secret for half a lifetime. After sketching his little tree into the B notebook in 1837, he had continued reading, gathering facts, pondering patterns, trying out phrases, brainstorming fervidly for another sixteen months in a series of such notebooks, labeled “C” and “D” and “E,” like a man pushing puzzle pieces around on a table. Then suddenly, in November 1838, as recorded in the E notebook, he solved the puzzle of how species must evolve. Combining three pieces in his mind, he hit upon an explanatory mechanism for evolution.

The first piece was hereditary continuity. Offspring tend to resemble their parents and grandparents, providing a stable background of similarity throughout time. The second factor, a countertrend to the first, was that variation does occur. Offspring don’t precisely resemble their parents. Brown eyes, blue eyes, taller, shorter, differences of hair color or nose shape among humans; wing markings in a butterfly, beak size in a bird, length of neck in a giraffe. Reproduction is inexact. Likewise, siblings, as well as parents and offspring, differ from one another. Darwin saw that these two pieces, heredity and variation, stand together in some sort of dynamic tension.

The third puzzle piece, which he had begun considering just recently, having been alerted to it by his eclectic reading, was that population growth always tends to outrun the available means of subsistence. Earth is always getting too full of life. One female cat may give birth to five kittens; one rabbit may deliver eight bunnies; one salmon may lay a thousand eggs. If all those offspring were to survive, and reproduce in their turns, there would soon be a very great lot of cats and bunnies and salmon. Whatever the litter size, whatever the lifetime fecundity, whatever the kind of organism, including humans, we all tend to multiply by geometric progression, not just by arithmetic increase—that is, more like 2, 4, 8, 16 than like 2, 3, 4, 5. Meanwhile, living space and food supply don’t increase nearly so quickly, if at all. Habitat doesn’t replicate itself. Places get crowded. Creatures go hungry. They struggle. The result is competition and deprivation and misery, winners and losers, unsuccessful efforts to breed and, for the less fortunate individuals, early death. Many are called, but few are chosen. The book that awakened Darwin to this reality was An Essay on the Principle of Population, by a severely logical clergyman and scholar named Thomas Malthus.

Malthus’s gloomy treatise was first published in 1798. It went through six editions in the next three decades and influenced British policy on welfare. (It argued against the relatively easy charity of the contemporary Poor Laws, which were soon changed.) Darwin read it in early autumn 1838–“for amusement,” as he recalled later. Seldom is amusement more productive. He came away with the population piece, combined that with his two other pieces, and scribbled an entry in his D notebook about “the warring of the species as inference from Malthus.” Yes, this “warring” applied not just to humans, Darwin realized, but also to other creatures. Competition was fierce, and opportunities were finite. “One may say there is a force like a hundred thousand wedges,” Darwin wrote, all trying to “force every kind of adapted structure” into the gaps in the economy of nature. “The final cause of all this wedgings,” he added, “must be to sort out proper structure & adapt it to change.” By “final cause,” he essentially meant final result: the struggle yielded well-adapted forms. That was the essence, though still inchoate and crudely stated.

Darwin seemed to leave Malthus behind as he finished the D notebook, but returned to him soon in the next. That one, labeled E, begun in October 1838, was bound in rust-brown leather, with a metal clasp. It’s one of the true relics in the history of biology. In its earlier pages, Darwin ruminated further about “the grand crush of population” and alluded repeatedly to what he now called “my theory.” He was growing more confident and clear. Then, on or soon after November 27, with his usual clipped grammar and eccentric punctuation, he wrote:

Three principles, will account for all

1 Grandchildren, like, grandfathers

2 Tendency to small change … especially with physical change

3 Great fertility in proportion to support of parents

Inheritance, variation, overpopulation. He saw how they fit. Put those three together and turn the crank: you’ll get differential survival, based on something or other. Based on what? Based on which variations turn out to be most advantageous. And those variations will tend to be inherited. The result will be gradual transmutation of heritable forms, and adaptation to circumstances, by a process of selective culling. Eventually he gave the crank a name: natural selection.

Twenty years passed after the E notebook entry. The world heard nothing about natural selection.

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It was a perplexingly long delay, almost two decades, between the writing of those four lines in his secret E notebook and the first public announcement of Darwin’s theory. Longer still, twenty-one years, to publication of the theory in book form—On the Origin of Species appeared in November 1859. The reasons for that delay, which were both scientific and personal, both anxious and tactical, have been minutely examined in other works (including some of mine). We can skip over them here except to note that, when Darwin finally went public with his theory, it was because a younger naturalist had forced his hand by coming forward with the same idea.

Alfred Russel Wallace, after four years of fieldwork in the Amazon and four more in the Malay Archipelago, had hit upon the notion of natural selection (framed in his own language, not that pair of words) and written it up in a short paper. As recounted by Wallace long afterward, the idea came during a layover in his collecting travels through the northern Moluccas. He suffered a bout of fever (maybe malarial), and, amidst it, he had this extraordinary insight. Variation plus overpopulation, minus the unsuccessful variants, would yield heritable adaptation. When the fever broke, and the sweat dried, and the dreamy brainstorm still seemed cogent, Wallace composed his manuscript and then tried to get it considered.

But he was a poor man’s son, working his way through the tropics by selling decorative specimens—bird skins, butterflies, pretty beetles—not a gentleman traveler as Darwin had been on the Beagle. Wallace wasn’t well educated or well connected. He knew almost nobody in the higher circles of British or European science, and almost nobody in those circles knew him—not face-to-face and not as a peer, anyway. He was a collector of dried creatures for pay, a natural-history tradesman. There was class stratification in science as in every other part of Victorian British society. But he had published a few earlier papers in a respectable journal, and one of those papers had drawn favorable attention from Charles Lyell, the great geologist. Oh, and Wallace knew one other famous man, not personally but as a sort of pen pal, who had spoken generously to him in a letter: Charles Darwin.