People are getting dumber. That's not a judgment; it's a global fact. In a host of leading nations, IQ scores have started to decline. Though there are legitimate questions about the relationship between IQ and intelligence, and broad recognition that success depends as much on other virtues like grit, IQ tests in use throughout the world today really do seem to capture something meaningful and durable. Decades of research have shown that individual IQ scores predict things such as educational achievement and longevity. More broadly, the average IQ score of a country is linked to economic growth and scientific innovation....