ANN ARBOR, Mich. – American teenagers are behaving better than their predecessors, according to the annual Monitoring the Future study, USA Today reports. Today’s teens are drinking less, smoking less and doing fewer drugs than other teens in four decades.

“The question is: Why is all this happening?” said Lloyd Johnston, survey leader since the program started in 1975. “Even though we have some hypotheses, I don’t know that we necessarily have the right ones.”

Johnston, who is with the University of Michigan’s Institute for Social Research, along with other experts, pointed to a drop in smoking as probably triggering the declines in drinking and drug use. For young teens, smoking can be a gateway to other unsafe activities.

In 1991, close to 11% of high school seniors puffed half a pack of cigarettes or more daily. In 2016, a mere 1.8% indicated they smoked that much, with 10.5% reporting any cigarette use during the last month. High school seniors also used electronic cigarettes less this year at 12% reporting usage, down from 16% in 2015. Alcohol usage has dropped to its lowest level with 37.3% of seniors reporting they’d been drunk at least once, down from the highest point of 53.2% in 2001.

“That is gigantic good fortune, and really I don’t think we as a field or society more generally have spent as much time as we should have celebrating and reflecting on why today’s kids are so great in this regard,” said Jonathan Caulkins, a drug policy researcher with Carnegie Mellon University.