With the possible exception of Asa Gray, no American read the Origin of Species with as much care and insight as Henry David Thoreau. Throughout the first week of February, he copied extracts from the Origin. Those notes, which until recently had never been published, comprise six notebook pages in a nearly illegible scrawl. They tell the story of someone who must have read with hushed attention, someone attuned to every nuance and involution in the book. In their attention to detail, they suggest someone who assiduously followed the gradual unfolding of Darwin’s ideas, the unspooling of his argument, as though the book of science were an adventure tale or a travel narrative.
He was drawn to Darwin’s compendium of facts, which illustrated the delicate interplay of causes leading to the survival or extinction of species. Darwin wrote, “The number of humble-bees in any district depends in a great degree on the number of field-mice, which destroy their combs and nests.” Thoreau copied the sentence into his notebook, probably because he enjoyed the cause-and-effect relationship it implied. He had always been interested in the quirky, arcane detail. “Winged seeds are never found in fruits which do not open,” he read in the Origin, transcribing the sentence into his natural history book. He recorded the strange (if incorrect) statement that “cats with blue eyes are invariably deaf,” something Darwin had gleaned from a work on zoological anomalies by Isidore Geoffroy St. Hilaire, who mistakenly assumed that all blue-eyed cats were deaf rather than the majority, as is actually the case.
He also admired Darwin’s genius for experimentation. Thoreau had described his own efforts in Walden to disprove the local myth that the pond was of unusual depth. With a stone tied to the end of a cod line, he “could tell accurately when the stone left the bottom, by having to pull so much harder before the water got underneath to help me”—a procedure that enabled him to chart the pond’s topography and discover its shallows and depths. He had even provided a map for interested readers. Now he discovered a similar impulse in Darwin. The British naturalist wanted to determine how far birds might transport seeds caught in their muddy feet; this would explain how identical plant species might be found thousands of miles apart. From the silty bottom of a pond near his home he procured some “three table-spoonfuls of mud,” which “when dry weighed only 6¾ ounces.” He kept the mud in his study for six months, “pulling up and counting each plant as it grew; the plants were of many kinds, and were altogether 537 in number; and yet the viscid mud was all contained in a breakfast cup!” The charm of the experiment resided in its simple ingenuity; from common household items Darwin had made a marvelous discovery: 537 plants!
Thoreau was most urgently drawn to Darwin’s ideas. That the struggle among species was an engine of creation struck him with particular force. It undermined transcendentalist assumptions about the essential goodness of nature, but it also corroborated many of Thoreau’s own observations. While living on Walden Pond, he had tried to discover the “unbroken harmony” of the environment, the “celestial dews” and “depth and purity” of the ponds. “Lying between the earth and heavens,” he wrote, Walden “partakes of the color of both.” But sometimes a darker reality intruded upon this picture. “From a hill-top you can see a fish leap in almost any part; for not a pickerel or shiner picks an insect from this smooth lake but it manifestly disturbs the equilibrium of the whole lake.” Something portentous and uneasy lurks about this sentence. The “simple fact” that animals must consume other animals to survive upsets Thoreau; it disturbs the equilibrium of one who wishes to find harmony and beauty in his surroundings. Thoreau tries to laugh it off, calling the dimpled lake the result of “piscine murder.” Yet Darwin provided an explanation for nature’s murderous subtext. Competition and struggle influenced “the whole economy of nature.” It drove species to change and adapt. It created. It was the cost of doing nature’s business.
By the time he finished the first chapters of Darwin’s book, Thoreau had seized upon two of its principal ideas. The first was variation: the essential building block of natural selection. Variation received more attention than any other topic in the Origin, mainly because it provided the “means of modification” that enabled organisms to adapt. In the past Thoreau had considered variation from a transcendentalist’s perspective. “I expected a fauna more infinite and various,” he noted with disappointment one spring day, “birds of more dazzling colors and more celestial song. How many springs shall I continue to see the common sucker (catostomus Bostoniensis) floating dead on our river! Will not Nature select her types from a new fount?” Written five years before Darwin’s book was published, the passage reveals a basic tenet of transcendentalist philosophy: Thoreau expects Nature to answer to the demands of his imagination, to serve human needs. But the dead fish he finds each spring in the Musketaquid River also suggested to him an imperfect fit between species and environment. Calling for more “types from a new fount,” Thoreau personifies Nature as a printer, able to produce new fonts with the prodigality of a poet who has sipped from the fountains of Hyperion. In this characteristic pun, Thoreau anticipated Darwin, suggesting that differences among individuals might eventually result in the diversification of species.
Following this line of thought now, he copied a number of passages about variation and hereditability, noting for instance the puzzling phenomenon of young horses born with stripes on their shoulders. Why did those stripes disappear as they aged? “How simply is the fact explained,” wrote Darwin, “if we believe that these species have descended from a striped progenitor, in the same manner as the several domestic breeds of pigeon have descended from the blue and barred rock-pigeon!” (Darwin’s point was that the history of a species was encoded in the body, that physical characteristics provided clues about relationships to ancient progenitors.) Thoreau also copied another remark under the heading “Variability of flowers,” which stated that species belonging to the same genus tended to share characteristics, such as variations in color, while those belonging to separate genera did not.
What really interested him, however, was Darwin’s discussion of geographical distribution—the same topic that had engaged Asa Gray a decade earlier. In 1850 Thoreau had noticed a pine seedling in his yard, miles from any other pine, prompting him to wonder how it had gotten there. He began to study the way squirrels transported nuts and seeds from one location to another; then he followed the aerial voyages of milkweed spores and dandelion seeds. Soon he was observing cockleburs and other barbed seeds that attached themselves to animals and clothing, and for a while he considered whether the railroad might play a role in dispersing nonnative seeds to new locations. The question he was trying to answer was one he had asked in Walden: “Why do precisely these objects which we behold make a world?” Thoreau wanted to understand how the oak and pine woods surrounding Concord had sprung into existence. Why did this locale support robins and butternuts rather than, say, parakeets and pecan trees? How had each living thing come to inhabit its particular spot on the planet?
By concerning himself with this topic, he was at the forefront of natural science. Alfred Russel Wallace, whose wide-ranging travels had given him keener insight into the distribution of living things than almost anyone else in the world, would eventually explain the significance of the problem in his book Island Life (1880): “We can never arrive at any trustworthy conclusions as to how the present state of the organic world was brought about until we have ascertained with some accuracy the general laws of the distribution of living things over the earth’s surface.” In his own travels on the Beagle, Darwin had discovered that physical barriers—oceans, deserts, and mountains—often confined plants and animals to highly circumscribed regions. The Galápagos Islands were but one example. Sometimes an identical species was scattered across distant continents, even across vast oceans—as in the case of the Japanese flora found in eastern North America. While Louis Agassiz claimed that such examples implied separate and divine creation, a consensus was beginning to emerge within the scientific community that species were migratory and dynamic, settling wherever climate and resources facilitated their growth.
Darwin was convinced that the distribution of plants and animals shed light on evolutionary development, especially when a species became isolated and developed on its own. Some of the most delightful passages in the Origin of Species describe the experiments he conducted to determine how organisms scattered across the globe. He immersed seeds in saltwater for months at a time, then planted them to see if they would grow. He calculated the distance these seeds might travel across the ocean while immersed. (He determined that some could travel as much as 924 miles by prevailing Atlantic currents.) As for animals, he placed duck feet in a tank of water containing minuscule freshwater snails to see if the tiny creatures would take hold of the webbing. Revisiting his old travel notes, he discovered that a water beetle blown onto the deck of the Beagle had traveled some forty-five miles; this led him to speculate how insects and birds might cover enormous distances during a gale.
These experiments not only revealed how the world might have become populated; they also suggested just how accidental was that process. Far from the carefully organized scheme Agassiz and other special creationists described, Darwin’s world was the product of random and haphazard occurrences. The seeds of plants blew wherever the wind took them and germinated wherever there was enough sun and moisture. Animals followed land bridges or were swept away by flash floods or hurricanes; they were isolated on tiny islands in the middle of the ocean. Nothing was predetermined, nothing organized by design. General laws might govern these actions, but at the individual level, chance prevailed.
Because he was already interested in the topic, Thoreau transcribed more passages from Darwin’s chapter on geographical distribution than from any other in the Origin. He carefully noted Darwin’s assertion that “I have not found a single instance, free from doubt, of a terrestrial mammal (excluding domesticated animals kept by the natives) inhabiting an island situated 300 miles from a continent or great continental island—.” And he meticulously followed Darwin’s argument that isolated islands might produce special evolutionary conditions. “[The French naturalist] Bory St. Vincent long ago remarked that Batrachians (frogs, toads, newts) have never been found on any of the many islands with which the great oceans are studded,” Darwin wrote. “I have taken pains to verify this assertion, and I have found it strictly true. I have, however, been assured that a frog exists on the mountains of the great island of New Zealand.”
Thoreau wrote down this passage and appended a remark that showed just how thoroughly he had absorbed the intricacies of Darwin’s discussion: The frog, he asserted, was surely “spawned not there.”
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Ultimately it was Darwin’s method that left the deepest impression on Thoreau. The book was infused with a point of view: humorous and humane, stubbornly rigorous, breathtaking in its originality. As Thoreau pored over the Origin, he encountered many of his own thoughts packaged and reformulated in a style that was not just scientific but something we would now call Darwinian. In Walden, Thoreau had described a natural world prodigious in death: “I love to see that Nature is so rife with life that myriads can be afforded to be sacrificed and suffered to prey on one another; that tender organizations can be so serenely squashed out of existence like pulp,—tadpoles, which herons gobble up, and tortoises and toads run over in the road; and that sometime it has rained flesh and blood!” Thoreau was again trying to place nature’s profligate waste within a larger philosophical context. Describing the stench of a dead horse “in the hollow by the path to my house,” he claimed that the fetid atmosphere of decomposition indicated “the strong appetite and inviolable health of Nature.”
Darwin’s theory was grounded on similar observations. Nature might be responsible for countless “exquisite adaptations” and “beautiful diversity,” as he put it, but beneath those adaptations and diversity was an incessant struggle. “Every one has heard that when an American forest is cut down,” he wrote, “a very different vegetation springs up. . . . What a struggle between the several kinds of trees must have gone on during long centuries, each annually scattering its seeds by the thousand; what war between insect and insect—between insects, snails, and other animals with birds and beasts of prey—all striving to increase, and all feeding on each other or on the trees or their seeds and seedlings, or on the plants which first clothed the ground and thus checked the growth of the trees.”
This picture of strife and competition is similar to Thoreau’s version of a natural world, “so rife with life that myriads can be afforded to be sacrificed and suffered to prey on one another.” But while Thoreau thought nature’s monumental destruction was necessary for its health, Darwin was less certain. “Throw up a handful of feathers, and all must fall to the ground according to definite laws,” Darwin exclaimed, “but how simple is this problem compared to the action and reaction of innumerable plants and animals which have determined, in the course of centuries, the proportional numbers and kinds of trees now growing on . . . old Indian ruins!” Nature was neither fable nor allegory; it was, rather, a handful of feathers falling as randomly as gravity allowed.
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Years earlier, when he was still living near the pond, Thoreau had been walking along the steep bank of the Fitchburg Railroad on the first warm day in spring when he noticed that the south-facing side of the embankment was thawing in the sun. “Innumerable little streams” of the softened sand and clay “overlap and interlace one another,” he observed, “exhibiting a sort of hybrid product, which obeys half way the law of currents, and half way that of vegetation.” The more he looked, the more interested he became in this odd sand foliage: “As it flows it takes the form of sappy leaves or vines, making heaps of pulpy sprays a foot or more in depth, and resembling, as you look down on them, the laciniated lobes and imbricated thalluses of some lichens.” Looking more closely, he was “reminded of coral, of leopards’ paws or birds’ feet, or brains and lungs or bowels, and excrements of all kinds.”
Generations of English students have puzzled over Thoreau’s unbridled enthusiasm for melting mud. His mounting excitement stems from a sense that he has cracked Nature’s code, has “stood in the laboratory of the Artist who made this world and me” and caught a glimpse of the source of all creation. This way of looking at nature is of course deeply romantic. Thoreau was influenced by Goethe’s Italian Journey, in which the German had theorized about a primordial “ur-plant” that served as the model of all subsequent plants. Goethe in turn had been influenced by Platonic forms; like Louis Agassiz, he believed there was an original, ideal plant upon which all subsequent plants were fashioned: “Otherwise, how could I recognize this or that form was a plant if all were not built on the same basic model.” Thoreau extended the analogy. For him the sand foliage represented “the original forms of vegetation”; it revealed nature’s blueprint. Then he made a leap: perhaps the flowing, branching mud revealed “the bony system, and in the still finer soil and organic matter the fleshy fibre or cellular tissue” of animals. After all, “What is man but a mass of thawing clay?”
You here see perchance how blood vessels were formed. If you look closely you observe that first there pushes forward from the thawing mass a stream of softened sand with a drop-like point, like the ball of the finger, feeling its way slowly and blindly downward. . . . Is not the hand a spreading palm leaf with its lobes and veins? The ear may be regarded, fancifully, as a lichen. . . . The nose is a manifest congealed drop or stalactite. The chin is a still larger drop, the confluent dripping of the face.
To his credit, Thoreau maintained a hint of skepticism throughout this rhapsodic passage. Riffing on words that sound like the mucky slithering of sand, he was really poking fun at himself, as if to say: Woe to anyone who embraces a theory for the tidiness of its explanation. But there is also genuine excitement at the prospect of discovering a law that might explain organic life.
Which is why Darwin’s conclusion surely made such an impression on him. Imagine the jolt of recognition Thoreau must have experienced when he came upon the book’s final paragraph:
It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. . . . Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
This is Darwin the visionary, rejoicing in nature’s profusion, its lush fecundity. The passage celebrates the complex and interdependent relationships among species that have developed over time, and its language vibrates with excitement—the same tremulous wonder with which Darwin recounted his youthful discovery of a new variety of beetle.
We tend to think of Darwin’s theory as one of grim determinism, of pointless change and purposeless death. But to do so is to miss a crucial point about his thinking during the period in which he wrote the Origin. In 1859 Darwin not only admired the natural world’s plenitude and capacity for transformation. He also believed that life’s messy process, its extravagant creation and destruction, led to something worth celebrating: “the production of the higher animals”—including, of course, humans.
Darwin’s portrait of a teeming, pulsating natural world deeply resonated with Thoreau. The Origin of Species revealed nature as process, as continual becoming. It directed one’s attention away from fixed concepts and hierarchies, toward movement instead. It valued moments of evanescent change above all others. If it endowed each organism with a history, it also pointed to a future that was impossible to predict.
For Thoreau, this aspect of the Origin seemed to finish a sentence he had long been struggling to articulate. Once uttered, that sentence seemed to snap the natural world into place. Reading the Origin, Thoreau discovered someone else who understood nature as he did: abounding and vibrant, each niche swarming, each interstice filled with life, each living thing a small part of constant change, a participant in struggle and development, brimming with potential and significance.
Throughout the late winter and early spring of 1860, he continued his daily walks, his diligent measuring and collecting. He spent the cold New England evenings hunched over his journal. But now his prose kindled with a new energy. And something else happened. For eight years Thoreau had patiently compiled mountains of phenological data—information about the timing of nature’s seasonal events. Over the years he had noted the flowering dates of hundreds of plants and recorded what environmental scientists now refer to as “leaf-out” and “ice-out” dates: that brief period when trees first show their leaves and when the ice on ponds melts.
Immediately after finishing Darwin’s book, Thoreau began the tedious task of extracting and collecting this information. He reread his journals—thousands of pages—and copied the relevant information onto random slips of paper. A receipt from the family pencil-making business, for instance, became the repository of phenological information from 1852. Snow levels from 1854, which Thoreau recorded with a notched walking stick, were written on another scrap. As he carefully combed through his journals, he placed an X by each entry he transcribed.
When he was finished with this monumental task, he found he had copied information about more than one hundred trees and some sixty shrubs. He had described the height of grasses, the size of red maple leaves in May, the dates during which the “leaves of goldenrod [were] obvious.” He recorded the growth of fir trees, of larches, the leafing-out of the fever bush, waxwork, red cedar, tupelo, red currant, poison sumac. He noted the day in which “chicadees have winter ways.” He entered the date on which he first noticed the scent of decay.
With this process complete, he gathered his slips of paper and transcribed the information once again. This time his data went into a series of spreadsheets. (The term spreadsheet was not in use then; it is possible Thoreau invented a prototype.) These sheets of paper were nearly the size of a newspaper. On each one Thoreau listed a month, with a column devoted to every year from 1852 to 1860. Into these columns, in tiny, nearly illegible handwriting, he recorded all the information he had gathered.
What was he up to? The simple answer is that we don’t entirely know. He may have been doing what scientists invariably do when their aggregated data become too large and unwieldy: organizing them into sets. But the painstaking work he began in 1860 enabled Thoreau to capture and quantify the processes of growth and death in nature—to discover patterns in nature’s chaotic creativity. It also allowed him to determine if Darwin’s theories held true in the natural environs he knew so well. In Walden he had precipitously leaped into wishful hypothesizing, drawing from a bank of thawing mud all sorts of conclusions about the human and the divine. The spreadsheets presented something radically different: a natural world sharply restricted to facts. If Thoreau hoped to find some law or principle that might unify nature, he now believed he first had to build a solid foundation of evidence.
Around this same time, he began incorporating ideas he derived from reading Darwin into a new lecture he was writing for the Concord Lyceum. That work was entitled “Wild Apples,” and it is arguably the first piece of literature on either side of the Atlantic to be inspired by the theory of natural selection.