This book focuses more on how the fossil and cultural (i.e., tool-making) evidence for early human ancestors illuminates various aspects of human nature and what it truly means to be human, rather than on the technical details and comparative anatomy of the different pre-homonid and homonid evolutionary lines. Leakey does spend some time discussing the fossils and anatomy, though, which would be almost impossible to avoid in a book on physical anthropology, of course, but it's not the main emphasis of the book. He's mainly interested in showing how the fossil record illuminates the important physical and cultural changes that occurred during our long evolution, and what that says about how early humans lived.
For example, Leakey discusses how the anatomical changes from early Australopithecus (Lucy) to Homo erectus suggest profound differences in the physiology and life style of our earliest ancestors versus the first and later homonids. During this evolutionary transition, all the following changes occurred: the prolonged, more helpless infancy of humans; our ability to be more active and athletic, more delayed sexual maturity; the ability to make and use finer tools; the ability to hunt and kill larger game, along with a more omnivorous diet; a more complex and sophisticated social structure; and finally, the development of true language. Leakey includes separate chapters on 'The Art of Language," "The Language of Art," and "The Origins of Mind," in which he discusses the evidence for these higher-level and more advanced cognitive processes. Leakey is also careful to discuss investigations ranging from traditional comparative anatomy to high-tech approaches using DNA techniques, microanatomy (such as tooth lines), and CAT scans.
Another important topic he discusses is how the fossil evidence has forced modifications in the conception of our evolutionary tree. Since I was last reading up on the subject, the tree has become much less linear and far more "bushy." Another hallowed and traditional idea that had to be abandoned was Darwin's own theory of primitive man being "special" and highly evolved even from the very beginning. As the fossil record has demonstrated, our evolution was far more gradual, with many intermediate homonids known for both H. sapiens and Neanderthal, such as the Sima de los Huesos and Petrolonas finds, which show that there were primitive, archaic Neanderthals in Europe who eventually evolved into the more modern types such as those found at Steinheim and Arago. For the pre-Homonids we now have Australopithecus afarensis, A. africanus, A. aethiopicus, A. robustus, and Australopithecus boiseii, as well as possibly two or different kinds of H. habilis, and so on. As I mentioned earlier, this has provided powerful support for a "bushier" family tree for human origins.
I only have one complaint, which is that the book, being now almost 10 years old, doesn't include the more recent finds of Ardipithecus ramidus and Sahelanthropus tchadensis, which together push our origins back several million years further even than "Lucy," at 3.6 million years, or Australopithicus afarensis.
Overall, however, a nice little introduction to the subject and the issues relating to our earliest origins, and I would give it four and a half stars if I could. After this book, you should have the background to tackle more technical books on the subject. If you decide to do this, I would recommend reading Richard Klein's book, The Dawn of Human Culture, next. It was published this year (2002), and discusses all the more recent finds in some detail. Klein's book is also probably the most readable and well-written account on the subject I've ever read, despite it's being at a fairly good technical level.
After you've finished with Klein's book, I would read Ian Tattarsal's Extinct Humans next, which is notable for the beautiful, high-gloss, color photographs of all the skulls, which is a great feature for comparing the descriptions of the comparative anatomy in the text to the actual specimens. It's also very well written, like Klein's book. In fact, the entire book is printed on very nice, high-gloss paper. The only downside is that this makes the book somewhat pricey compared to the other books here.
I have one more recommendation, which is that you could follow Klein's book with Neanderthal, by Paul Jordan. It's the only book I've seen covering the one genus, although Jordan includes chapters discussing the earlier and later homonids, too, but the emphasis is definitely on all the Neanderthal finds and their significance. It makes for more technical and somewhat dry reading, but does cover the subject in a more detailed way than any of the other books I've seen.
After reading these four books, you'll have covered the best current writing out there on the subject, along with all the major fossil finds. As I said, the only one missing from these books is the M. Brunet expedition's discovery of Sahelanthropus tchadensis, and you could just look up some online articles about it to get the scoop on that. Also, Time magazine had a major article on it in the July 22, 2002 issue, so you could try looking up that, too, at which point, you'd have covered everything.
Hope my little comparson review of these books helps. Good luck and happy reading!