As someone who doesn’t attend yoga or spin classes, my interest in athleisure doesn’t have much to do with practicality—or style. I’m a fairly boring jeans-and-button-up kind of guy. But for years, I’ve been wondering what athleisure’s rise says about modern culture and the way groups decide to embrace one idea and discard another. Yoga’s been around for millennia. Stretchy fabrics have been around for decades. So, what made athleisure take off so suddenly?

Read: The psychology of Lululemon—how fashion affects fitness

Deirdre Clemente has an answer. A fashion historian at the University of Nevada Las Vegas, she says athleisure is the culmination of three long-term trends. First, technological improvements to synthetic fiber have made products like spandex more flexible, durable, and washable than natural materials. Second, the modern fixation on healthy appearance has made yoga pants an effective vector for “conspicuous consumption,” Thorstein Veblen’s term for products that confer status—like “extremely healthy person”— upon their owners. Finally, the blurring of yoga-studio fashion and office attire snaps into the long decline of formality in American fashion.

“One hundred years ago, you would have day clothes for the street, dinner clothes for the restaurant, theater clothes, and so many genres of dress,” Clemente said. “Those barriers have come down. Athleisure is the ultimate breaking down of barriers.”

To Clemente, the athleisure story doesn’t begin in the late 20th century, with the birth of Lululemon. It begins in the late 19th century, a sort of Cambrian Explosion moment for basic fashion when sports changed the way young people dressed—both on the field and in the classroom.

In other words, when I asked Clemente to explain the sudden rise of athleisure, my request was one word too long. There is nothing sudden about the influence of sports on the way Americans dress. In fact, it is hardly an exaggeration to say that all modern fashion is athleisure.

The late 19th century was transformative for two reasons.

In 1892, the U.S. Rubber Company began producing shoes with rubber soles, and its target consumers were athletes. The friction of rubber offered superior grip for fin de siecle sportsmen in lawn sports and on tennis courts; hence, the name tennis shoe. (The long-standing alternative sneaker allegedly refers to the fact that rubber-soled shoes don’t click and clomp on hard surfaces, which allows their wearers to sneak up on people.) Although the popularity of tennis has been declining for decades, today almost all of the best-selling shoes in America are sneakers. Like yoga pants, tennis shoes are sportswear that have transcended their sport.

Around the same time as the invention of the rubber sole, intramural sports took off at American universities, Clemente told me. That meant more young men playing tennis, golf, polo, and croquet. But lacking the means or inclination to fill their wardrobe with non-sports clothes, many of these men simply kept their athletic attire on for class. Athleisure dropped the prefix and became, simply, leisure.