1491 is a summary of recent changes in (scholarly) understanding of the peoples in the Americas immediately before Columbus. Part I argues that there were many more people here than you think. Part II argues that they got here much earlier than you think. Part III argues that they had a much larger impact on the environment than you think. The new understanding of the Americas is really cool. I just wish that the book had been written by one of the scientists, instead of a professional popular science writer. It is obvious to me, from reading it, that the author is not and never has been a scientist.