I thoroughly enjoyed reading Jared Diamond's "Guns, Germs, and Steel: The Fates of Human Societies" and have recommended it to many others. But I was looking at it again today and reminded of the untruth at its very foundation.
At the beginning of the book--literally, the second page of the Prologue--he says: "He [Yali, a New Guinean friend of Diamond's] and I knew perfectly well that New Guineans are on the average at least as smart as Europeans." This is simply false. The average IQ in those European countries is around 100 or a little lower; the average in Papua New Guinea is around 85 or a little lower.
With Google, this is easy to confirm nowadays. But even in the pre-Google days that Diamond was writing the book, the data were pretty readily available to a scholar like him. So either he *knew* he was writing falsely, in which case he just plain lied; or he *should* have known that his statement of equal intelligence was false, in which case his research on this point was culpably shoddy.