My book is about a historic change that occurred a century ago in the way people view human differences, illustrated through the work and life of a major artist. Today, we routinely use the word “cultures” to describe complex bodies of human behavior, or customs, formed by groups of people through social interaction over time. Nowadays, one’s “culture” is an important part of one’s identity. Because we recognize that any human being can potentially learn any human behavior, though, we also acknowledge that cultures are not etched in stone. Indeed, they can change, especially in our interconnected global community where people move frequently and communicate instantaneously.Using the word “cultures” in this plural, changing sense only became widespread in the early twentieth century, after anthropologists Ruth Benedict and Margaret Mead (students of Franz Boas at Columbia) popularized the term in the 1920s and 1930s. Before then, most people viewed human group behavior differently. They saw the behavior of different groups as “natural”—ostensibly determined by “race,” impervious to change regardless of nationality, environment, gender, and class. Most educated people today view human groups more as evolving social entities, or “cultures.” Historians of anthropology consider the emergence of the concept of “cultures” in the twentieth century to be a major watershed, distinguishing modern from pre-modern ways of understanding human behavior. The modern concept of “cultures” has played a central role in challenging racism and biological determinism, because it acknowledges the fundamental capacity of all human beings to learn and exchange virtually any pattern of human behavior.Thomas Eakins and the Cultures of Modernity situates an important American artist in relation to that watershed development. Whereas many art historians have attributed a modern perception of “cultures” to Eakins, my book demonstrates that the artist – who died in 1916 – did not use that term and could not have perceived human differences like a modern anthropologist. Rather, Eakins’s realistic portrayals of diverse groups of people – Spanish street performers, African Americans, southern European immigrants, Anglo-American scientists – embodied a pre-modern worldview, which confused “race” with social behavior. Yet, Eakins’s struggle to visualize human diversity amid the changing demographics and dislocating forces of his day – mass immigration, tourism, commercial publishing, and ethnographic museums – illuminates American art on the threshold of the twentieth-century concept of “cultures” in plural.