An astonishing new study that delves into the lives of teens finds that they are growing up more slowly than they used to, eschewing adult activities like sex and drinking alcohol while gravitating more toward things like outdoor hobbies or education. It’s certainly a nice discovery if you’re a parent, but it’s caused scientists to wonder why that is, and they’ve come up with some theories.

The study, published in the journal Child Development, found that the number of adolescents who have a driver’s license, have tried alcohol, date, or work has plunged since 1976, and especially in the last decade. And the difference appears to be consistent across race, socioeconomic, and geographic lines. And while more than half of teens engage in these activites, the majority is no longer as strong as it once was, with 63 percent of high school seniors reporting they had gone on a date compared to 86 percent in the 70s, for example.

Scientists theorize that kids may be less interested in these activities because they no longer need to engage in these activities. An exposure to “harsh and unpredictable” environments forces teens to develop faster, while those in a secure environment may be able to explore other things since they aren’t in survival mode.

“The developmental trajectory of adolescence has slowed, with teens growing up more slowly than they used to,” explains Jean M. Twenge, professor of psychology at San Diego State University and the lead author on the study. “In terms of adult activities, 18-year-olds now look like 15-year-olds once did.”