Much of Johanson's work is quite thorough. He goes to great lengths to lean on the specialized knowledge of experts in many different areas of science, and does a beautiful job of weaving them together for a plausible view of our "ancestor", as he refers to the title skeleton find, a 40% complete skeleton of australopithecus afarensis. Of course, no respectable modern paleoanthropologist would consider Lucy to be our ancestor today, but Johanson's analysis is interesting nonetheless.

Another of Johanson's follies is his dependence upon "the Lovejoy hypothesis" of bipedal locomotion being a biological response to a need to carry food and tools. While this is interesting in and of itself, I would recommend reading Richard Leakey/Roger Lewin's rebuttal to Lovejoy in their "Origins Reconsidered..."

Overall, this book is best described as a historical document. Much of its scientific value is reduced to an example of how controversial the major finds of human ancestors will always be.