When Cathy Newman’s superiors at the National Geographic Society asked her to write the text for a new book about fashion, Newman had to ponder some unusual questions: “Is there a relationship between the skirt of a whirling dervish and a cowboy boot? Is there a relationship between a South American Indian’s body tattoo and that of a punk-rock kid?”

“In the end,” Newman says, “I concluded, ‘Yeah, there is.’”

Fashion—a large-format, 240-page book that is Newman’s third for the society—features 200 photographs drawn from the NGS’s century-old archives. With the exception of some recent images taken at haute couture shows in Europe, most of the photographs were made without intending to chronicle fashion per se; most—the piercings of an African tribesman, the kimono of a Japanese geisha, the sari of an Indian woman—were taken to illustrate articles about cultures across the globe.

Newman, 51, explores how we define fashion—and how fashion defines us—through essays and interviews with a range of scholars, designers, retailers, and ordinary people in both Europe and America. “Of course, fashion is frivolous,” famed designer Vivienne Westwood tells Newman in the chapter “Frivolous or Functional?” “It should be. It has to be, to be seductive.” In the same chapter, D.C. bike courier Rafael Misher attests that fashion is also created through necessity: After a serious on-the-job injury, Misher jury-rigged a special padded suit—Newman describes it as a “Power Ranger look”—that wound up saving him from getting hurt in a subsequent collision.

Ultimately, Newman concluded that fashion boils down to communication. “Fashion says, ‘Look at me. I am a member of this tribe or this culture or this socioeconomic level or this rank,’” she says. “It’s a badge we wear on our bodies that immediately signifies to the world who we are, or who we think we are, or who we would like to become.”

Newman, a resident of Northwest D.C., has written about a range of topics—from the Shakers to trout to Silicon Valley—during her 23 years with National Geographic. She says that her interest in fashion dates back to her friendship with Nina Hyde, the late fashion writer for the Washington Post. “I was always impressed that Nina understood that fashion was, or could be, a serious subject,” she says. “People think of it as frivolous, but Nina understood that there was more to fashion than the length of a hemline.” —Louis Jacobson