“How old were you the first time you had sexual intercourse?”“In warm weather, how often do you sleep nude?”“Do you have sexual dreams?“

The Kinsey Institute at Indiana University has been studying human sexuality and asking questions such as these for 75 years.

Alfred Kinsey, the famed sexologist, founded the organization in 1947. He’d started studying human sexuality years earlier, when the university asked him to teach a course on marriage and family. To prepare, he looked for scientific research on human sexual behavior. Finding little, he conducted his own, and in the process changed the way we think about our sex lives.

Armed with a list of roughly 350 questions, Dr. Kinsey and other researchers criss-crossed the country interviewing thousands of Americans about their sex lives. This body of research formed the basis for two landmark books: “Sexual Behavior in the Human Male,” published in 1948, and “Sexual Behavior in the Human Female,” published five years later.

Kinsey-affiliated researchers—anthropologists, biologists, sociologists and psychologists—have since studied everything from reproduction and sexual health to homosexuality and gender development. Kinsey researchers were the first to conclude that sexual orientation is on a continuum and not an either/or. They held influential conferences on HIV and AIDS in the 1980s. More recently, they began a longitudinal study on the pandemic’s impact on our sexuality and intimate relationships. (Fun finding: One in five people have tried something new sexually during this time.)

“We are trying to take this experience that millions of people have every day and shed some light on the mystery of it,” says Justin Garcia, Kinsey’s executive director.

As the Kinsey Institute celebrates its 75th anniversary this week, I looked at a few of the top discoveries its researchers have made about our sex lives.