53. Slan by A. E. Van Vogt
I can definitely see why this book is considered a classic. Although some of the perspectives and ideas that Vogt has about the future are a bit dated, the story itself is clearly the basis of every other book I have read about human evolution. When I read Darwin's Radio by Greg Bear, I thought it was so original, but now I see that it is not. It's still a good book, but Vogt came up with the major themes many years earlier. The book is very short, but packed with ideas. No word is wasted, and the story moves quickly. Very impressive, and I am glad I read it.