“Of course, a smartphone opens up worlds of new possible experiences, including video games (which are forms of play) and virtual long-distance friendships. But this happens at the cost of reducing the kinds of experiences humans evolved for and that they must have in abundance to become socially functional adults. It's as if we gave our infants iPads loaded with movies about walking, but the movies were so engrossing that kids never put in the time or effort to practice walking.”