Two years ago, the social psychologist Jonathan Haidt’s book about the dangers of social-media became a best-seller—and the subject of some critical eye-rolling. Now, for many, it’s become essential.

While exploring caves along a riverbank, a group followed a tunnel that quickly led deep underground. The passage opened into massive chambers filled with crystal formations and towering limestone ...

The researchers were hoping to understand whether our own species' long documented appreciation (bordering on obsession) with crystals ...