Textbooks should admit uncertainty. The very first thing that we teach in U.S.-history courses is when and how people first got to the Americas. The best answer is: We’re not sure. But the darned textbooks don’t say that—except for one of the 18 textbooks I studied intensively. Ironically, it’s the oldest one—it was published way back in the 1970s, and it says something like: The information in this section may be outdated by the time you read it. And by just saying that, it turns out to be the only textbook that is not outdated, even in 2018.