“NOW IS BETTER.” The bold logo, emblazoned on a stylish tote bag, caught my eye recently at a favorite museum shop. The tote cleverly served as both self-help logo and advertisement for the contemporary art exhibition I’d just viewed. The high-concept show had centered on the psychology of human happiness, and this was one of its chief precepts. But as appealing as the slogan was at first sight, upon further reflection, it seemed insufferably smug.

I’d just read the multidisciplinary scientist and bestselling author Jared Diamond’s provocative new book, The World until Yesterday: What Can We Learn from Traditional Societies? and one of his first lessons is that we don’t all live in the same “now”—or even necessarily share the same psychological assumptions or expectations. Indeed, he writes, “Psychologists base most of their generalizations about human nature on studies of our own narrow and atypical slice of human diversity.” As a result, he continues, “Most of our understanding of human psychology is based on subjects who may be described by the acronym WEIRD: from Western, educated, industrialized, rich, and democratic societies.”

By contrast, his decades of living for extended periods among traditional peoples in isolated regions of the Pacific Islands has taught Diamond just how weird Western societies can seem when seen through the lens of small-scale societies. To begin with, he writes, “Many of my New Guinea friends count differently (by…