But that's not really shocking, says Lisa Wade, PhD, a professor of sociology and author of American Hookup . Hookup culture is just the latest iteration of dating, which changes all the time. In fact, people didn't really have anniversaries (apart from their wedding anniversaries) until the 1950s, she says. We have the idea of "going steady," meaning that it's normal to have a long-term monogamous relationship before getting married, because of World War II. "The New York Times was telling young women that they lost 800,000 men in World War II," she says. And that's true. Lots of men died, many married women from overseas, and many came back knowing that they were gay because they were able to explore their sexuality while at war. "There was a big media push telling young women that they better nail down their guys early, because if they didn't get a guy they'd be an old biddy for life," Dr. Wade says. "So women invented going steady to try to make up for all the men that were gone."