“May you live in interesting times,” the proverb goes, and it is an open question, still, whether those on the receiving end of the entreaty should consider themselves to have been just blessed, or just cursed. History itself, at any rate, is biased toward interestingness. It tends to favor, in its selective memory, the moments and the monuments, the stuff of revolutions and paradigm shifts. Its workings tend to sand away the rough edges of small lives, messily lived, to focus instead on singular instants of epochal change: Darwin found his finches, and Newton plopped down under the apple tree, and Galileo peered through glass to see the stars, and nothing would ever be the same again.

But history as it’s made is much more chaotic than history as it’s written might suggest. That is one of the ideas at play in The Book That Changed America: How Darwin’s Theory of Evolution Ignited a Nation, Randall Fuller’s new exploration of how one particular paradigm shift—the one brought about by Darwin’s On the Origin of Species, published just before the start of the Civil War—affected the survival of the United States, as a nation and as an idea. Fuller is a professor of English (he is also the author of Emerson’s Ghosts: Literature, Politics, and the Making of Americanists and From Battlefields Rising: How the Civil War Transformed American Literature), and his latest book is, like its predecessors, especially attuned to the human hums of history. It focuses on a small group of prominent thinkers—Henry David Thoreau, Ralph Waldo Emerson, Bronson Alcott, Charles Loring Brace, Louis Agassiz—as they wrestled with a theory that would help the young nation to struggle and adapt and evolve, finally, into something better than it was before.

In July of 1860, Asa Gray, the Harvard botanist, published a book review in The Atlantic Monthly, a fledgling periodical founded in Boston and “Devoted to Literature, Art, and Politics.” The essay—the first of three Gray would write for the magazine—considered the implications of Darwin’s On the Origin of Species (full title: On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life), which, published in England in 1859, had recently reached American shores. Gray’s review would provide many Americans’ first introduction to the theory that would challenge their notions of God, morality, and the nature of the human soul. It began, as such, with a discussion of pants.

“Novelties,” the eminent naturalist began, “are enticing to most people: to us they are simply annoying.”

We cling to a long-accepted theory, just as we cling to an old suit of clothes. A new theory, like a new pair of breeches, (“The Atlantic” still affects the older type of nether garment,) is sure to have hardfitting places; or even when no particular fault can be found with the article, it oppresses with a sense of general discomfort. New notions and new styles worry us, till we get well used to them, which is only by slow degrees.

Slacks, yes, but also slack: Gray understood the effusive implications of On the Origin of Species, and he framed his review around his conviction that Darwin had written a book that was as much about history’s unsteadiness as it was about nature’s. He foresaw the way Darwin’s deceptively elegant theory would challenge long-standing—and comforting—assumptions: not just about the relationship between the physical and metaphysical worlds, but also about the fixity of the universe, about the forward march of progress. Gray tried, in introducing all that to lay audiences, to offer reassurance alongside all the disruption: New notions and new styles worry us, till we get well used to them. They will chafe and distract, until—slowly and suddenly—they are a second skin.

Gray was careful in his wording not just because he was scientist, but also because he was introducing the incendiary book to the American public during a time that was, itself, particularly prone to fires. On the Origin of Species arrived in the U.S. during the time just before the Civil War became an inevitability—and during a time, as well, when slavery’s evil still resided in the sphere of legitimate debate. Gray’s review of Darwin was delivered to American libraries and living rooms in an era when it was still revolutionary—and, even to the most progressive citizens, shocking—to suggest that humans were part of nature, rather than its masters.

Today, the cultural anxiety Darwin is most commonly understood to have initiated is the one about God’s place in human existence, and vice versa; we tend to think of him as having provoked a fight that would rage on into the Tennessee courtrooms of the 20th century and the American classrooms of the 21st—a fight that, as it was stirring in the 19th, would lead Emily Dickinson to declare, “[W]e thought Darwin had thrown ‘the Redeemer’ away.” And, certainly, he had done a little of that.

As Fuller demonstrates, though, On the Origin of Species was controversial in its time as much for its biological arguments as for its theological implications. The book was written in a generally genial tone; Darwin largely left the men-and-monkeys and humans-and-God business for others to infer. That style helped him to disguise, Fuller suggests, one of the book’s most explosive subtexts: Darwin’s theories, on top of everything else, challenged the assumption, commonly held in 19th-century America, that humanity was inexorably improving—that man, created in God’s image, was moving ever Godward. If evolution (a word Darwin used sparingly in the book) occurs randomly, without the intervention of divine will and protection—natural selection, after all—then change itself can occur not just for the better, but for the worse. The world, so wonderfully capable of evolution, is just as capable of the opposite.

It was a troubling idea; it was also, potentially, a liberating one. Asa Gray, for his part—a scientist who also held, like many of his peers, a deep religious faith—adopted an accommodatingly synthetic view of this element of Darwin’s (meta)physics. The botanist read Darwin’s theory not as some of his contemporaries would—as a direct challenge to God’s creative agency—but rather as a scientific explanation of divine power working its will upon the world. Natural selection was simply a mechanism, Gray thought—and, in its way, a manifestation—of the divine.

In this, Gray shared a reaction to On the Origin of Species with Henry David Thoreau, who is best remembered today as the controversial “hermit of Concord,” but who was also a natural scientist in his own right. (Thoreau, Fuller notes, once fashioned a platform that he installed into the crown of his hat, the better to store the samplesflora, fauna, whatever struck his fancyhe picked up during his wanderings.) Thoreau, too, might well have invented the spreadsheet, Fuller suggests; he used charts to obsessively catalogue the wildlife he observed around Walden Pond and its environs. It was his abiding communion with nature that had long led Thoreau to suspect, Fuller also notes, that “humans and animals were part of the same continuum.” Darwin’s theory provided a scientific foundation for that belief.

Thoreau is also remembered, today, as an intellectual forerunner of the civil rights movement—an early advocate, with work that would later inspire Dr. King, of passive resistance in the face of institutional immorality. (A staunch abolitionist, Thoreau refused to pay taxes—and was briefly jailed for the refusal—on the grounds that he preferred his money not abet a government that abetted the evil institution.) On the Origin of Species first arrived on American shores, as it happened, just after the radical abolitionist John Brown was executed for his failed attempt to initiate an armed uprising of slaves, at Harper’s Ferry. The notion of natural selection, then, came to the United States as the nation was passionately debating whether Brown had died a traitor or a martyr. The theory helped, Fuller suggests, to crystallize Thoreau’s thinking, and that of many of his fellow intellectuals, about slavery—the most divisive, and in some sense the only, topic of the day.

Social Darwinism and its unsavory implications would come later. Those early readers of On the Origin of Species, Fuller argues, interpreted the book as compelling evidence for abolition. The book’s theories implied, after all, that humans are indeed members of one species (this was, at the time, another matter of legitimate controversy). Many slave-holders had clung to the notion that different races were also different species—an attempt to justify themselves to each other and to history. Darwin’s theory adroitly refuted their arguments. And the abolitionists exulted in the refutation. “On the Origin of Species swept through Boston like a choice bit of gossip,” Fuller writes; that was in part because the book afforded slavery’s opponents the spark they needed to set fire to the era’s most looming of straw men.

Which is not to say that the book was universally accepted, even among the small group of East Coast intellectuals Fuller focuses on. Many of the early readers of On the Origin of Species, he suggests, rejected Darwin’s findings outright. One of them: Bronson Alcott, the father of Louisa May and a committed transcendentalist. Alcott mistrusted science, in general, on the grounds that its practice failed to account for divine will. He deemed Darwin, despite the naturalist’s ingenuity, to have presented a vision of the world’s workings that was “destitute of spirit.” It was one of the worst insults Alcott could think of to aim at a fellow philosopher.

Another critic of Darwin was Louis Agassiz—who was, like Gray, a Harvard biologist, and who is, unlike Gray, The Book That Changed America’s unofficial villain. Agassiz was brilliant: He was one of the first scientists to suggest that Earth had undergone an ice age. He was also a devoted racist who believed that God had placed humans and animals—as fixed and separate species—into specialized “Zones” for which they were best suited. To Agassiz, Fuller notes, “it was inconceivable that whales and lions could be linked by anything other than their mutual conception in the mind of the creator.” Agassiz thus informed Gray, to the latter’s evident amusement, that Darwin’s work was “poor—very poor!” In the margins of his copy of On the Origin of Species, Agassiz was blunter still: “This,” he wrote, “is truly monstrous!”

Humans are small until they are big. Revolution happens gradually, until it happens suddenly. Ideas appear, and evolve, until they die away or become part of the air we breathe. The Book That Changed America is, as a title, as compelling as it is sweeping; its post-colon, however—How Darwin’s Theory of Evolution Ignited a Nation—is more descriptive of the book’s accomplishments. Fuller’s tale is of Darwin and abolition and moral battles that led to literal ones; it is also, more simply, the story of humans wrestling with insights that would change the world and their place in it.

The story is evocatively told: Fuller is an excellent writer, with an eye for irony and a unique ability to inject suspense into a story that is, at its core, about the mercurial nature of chromosomes. The book is also, in some ways, as limited as it is sprawling. It focuses on the intellectual elites—and on their pettiness, and their idealism, their humanity. As for the broader “America,” though—its everyday denizens, among them wide swathes of people who were not yet afforded the dignity of citizenry—Fuller offers less detail. The Book That Changed America is an intellectual history that reads as a drama; drama is not something that easily scales.

But determined humanity is a value much more than a drawback. And while The Book That Changed America may be an entry in the history of ideas, its primary concern is the people who are at once ideas’ creators and their recipients. Before Darwin’s theories could shift their paradigms—before, indeed, they could help to Change America at all—they had to prove themselves within the lush and harsh environs of the human mind. Darwin found his finches; the ideas they sparked in turn ignited debate between Emerson and Thoreau, between Alcott and Gray, between Gray and the far-flung readers of The Atlantic Monthly. The ideas struggled. They adapted. They inspired. They lived and breathed in the most tumultuous of times. They helped to ensure that those times—and the many that would follow in their pathwould be occasionally blessed, occasionally cursed, and either way deeply interesting.