 Now, what could possibly have been responsible for this radical rise? Haidt pinpointed two villains. He said that parents, starting in the 1980s, no longer allowed their kids to go off with their friends and play without adult supervision. Haidt cited research indicating that this sort of play is necessary to wire up the brains of all mammals, including us humans, and Haidt called this the decline of play-based childhoods. That was villain number one.