Amazon.com description: Product Description: The dominant idea of this book is that of progress. Morgan conceived it as a career of social states arranged in a scale on which man has worked his way up from the bottom. Progress is historically true of the entire human family, but not uniformly. Different branches of the family have evidenced human advancement to different conditions. He thought the scale had universal application or substantially the same in kind, with deviations from uniformity ... produced by special causes.