In the 1930s, a cohort of professional human scientists coalesced around a common and particular understanding of objectivity as the foundation of legitimate knowledge, and of fieldwork as the pathway to objectivity. Into the Field is the first collective biography of this cohort, evocatively described by one contemporary as the men of one age.

At the height of imperialism, the men of one age undertook field research in territories under Japanese rule in pursuit of "objective" information that would justify the subjugation of local peoples. After 1945, amid the defeat and dismantling of Japanese sovereignty and under the occupation and tutelage of the United States, they returned to the field to create narratives of human difference that supported the new national values of democracy, capitalism, and peace. The 1968 student movement challenged these values, resulting in an all-encompassing attack on objectivity itself. Nonetheless, the legacy of the men of one age lives on in the disciplines they developed and the beliefs they established about human diversity.