The compelling story of the effect of Charles Darwin's book On the Origin of Species on a diverse group of American writers, abolitionists, and social reformers, including Henry David Thoreau and Bronson Alcott, in 1860.

In early 1860, a single copy of Charles Darwin's On the Origin of Species was read and discussed by five important American intellectuals who seized on the book's assertion of a common ancestry for all creatures as a powerful argument against slavery. The book first came into the hands of Harvard botanist Asa Gray, who would lead the fight for the theory in America. Gray passed his heavily annotated copy to the child welfare reformer Charles Loring Brace, who saw value in natural selection's premise that mankind was destined to undergo progressive improvement. Brace then introduced the book to three other friends: Franklin Sanborn, a key supporter of the abolitionist John Brown, who grasped that Darwin's depiction of constant struggle and endless competition perfectly described America in 1860, especially the ongoing conflict between pro- and antislavery forces; the philosopher Bronson Alcott, who resisted Darwin's insights as a threat to transcendental idealism; and Henry David Thoreau, who used Darwin's theory to redirect the work he would pursue till the end of his life regarding species migration and the interconnectedness of nature.

The Book That Changed America offers a fascinating narrative account of these prominent figures as they grappled over the course of that year with Darwin's dangerous hypotheses. In doing so, it provides new perspectives on America prior to the Civil War, showing how Darwin's ideas become potent ammunition in the debate over slavery and helped advance the cause of abolition by giving it scientific credibility.