In this book, science writer Carl Zimmer sets out to give a brief overview of human evolution that is timely, accessible, and suitable for the intelligent general reader. This is a task many writers have attempted, but few have succeeded as well as Zimmer does. He strikes a superb balance between a highly readable style and a sophisticated scientific content, judging precisely when to stop and explain basic concepts essential to the larger points he is making.
Much of what will appeal to readers is the clear, jargon-free prose. Zimmer does an excellent job of writing directly and summarizing the high points of theories without "dumbing down" the content. He manages to review the history of Darwin's development of evolutionary theory in the absence of any genetic information and switches back and forth between fossil discoveries and living primates with ease.
Zimmer also provides an excellent, brief explanation of DNA and its uses in establishing the relationships among living forms as well as what DNA can and cannot say about extinct species. These can be daunting subjects, but Zimmer shows how straightforward and understandable genetics can be when properly explained.
The author emphasizes the abundant evidence that modern humans and apes shared a common ancestor while pointing out the fallacy of thinking that modern humans are descended from living apes, when in fact, both have evolved for millions of years since their divergence from a common ancestor. Since creationists and "intelligent design" advocates are still confused by this subtlety, it is heart-warming to see a book that clearly explains the difference between having a common ancestor and being descended from one another.
Zimmer recounts some of the history of fossil hominin discoveries and the evolution of different species of hominins. In one section, he discusses the seemingly contradictory anatomical evidence that early hominins were both bipedal and tree-climbing. Without attempting to force a false resolution, Zimmer presents several different lines of research. He brings in information about when living primates that are predominantly quadrupedal resort to bipedality; he considers ecological reconstructions of the landscape in which bipedalism evolved; and he presents computerized studies of the advantages and disadvantages of being bipedal with different stances and types of anatomy.
The book touches on many important developments that occurred during human evolution: tool-making, the origin of language, the appearance of art and ornaments, the origin of modern humans and our spread around the globe. The reader is given just enough fascinating information to be hungry for more.
My favorite section is the discussion of a classic experiment with Kanzi, a bonobo who was encouraged to make stone tools. A banana was placed in a box that was tied shut with a rope. Kanzi was shown how to strike a sharp-edged flake from a pebble by archaeologist and expert knapper Nicholas Toth. Kanzi was also shown how to use the flake to cut the rope and get the banana. Kanzi watched Toth with intense interest, yet was unable to remove a single flake in the fashion Toth had shown him though he tried repeatedly. Eventually, Kanzi created his own successful toolmaking technique. He hurled the stone against the floor until it smashed into sharp fragments, which he immediately snatched up to cut the rope and get the banana.
At the outset, this experiment was designed to test the hypothesis that modern apes do not make flaked stone tools because they have not been taught how to; the banana provided the motivation. Like all truly elegant experiments, the results not only answered the original question but also revealed the flaws in the experimental design. Kanzi the tool-maker showed that our interpretations of the past are hampered by the limits of our experience.
Was it a failure that Kanzi could not make flaked tools — or was it a creative success that Kanzi invented a new way to obtain sharp stone pieces to cut the rope? Clearly there is more than one way to get the banana. Chimps are not early hominins and early hominins are not simply hairy humans lacking modern technology.
A significant part of what will attract readers is the book itself. It is a good size (larger pages than a standard text but fewer than 200 of them) and it has many wellplaced color illustrations. The book looks interesting and is. I found no dead spots where general readers would roll their eyes in boredom and put the whole thing down.
The biggest failing of the book, sadly, is also in the illustrations. For example, in a section on methods of dating rocks, there is a photograph of foraminifera (very tiny water-living creatures that make shells used to date rocks about 500 million years old) and a drawing or painting of a reconstruction of a conodont (one of the most primitive vertebrates, used to date geological strata of 500 to 250 million years ago). Neither conodonts nor foraminifera are very pertinent to dating the human evolutionary record, which goes back only about 7 million years.
Troublingly, some of the illustrations do not show what they purport to show. The "gorilla skull at Down House, Charles Darwin's residence" is a female baboon skull and the "drawing of Java Man, a Homo erectus fossil" is a photograph of a chimpanzee skull. Both of these erroneously labeled illustrations came from the same photo library, which ought to be a warning to future science writers. The intelligent reader is likely to wonder why these illustrations do not jibe with information in the text.
Sadly, the illustrations are in a sense wasted space. They look lively and interesting but they do not further the readers' understanding of the subject. For example, one image shows a chimp skull and a human skull, which could be used to demonstrate the anatomical differences that make apes apes and humans humans. The caption says, "A chimpanzee skull, left, compared to a human skull." This illustration is merely wallpaper, not a means of conveying information.
Nonetheless, I would recommend this book to general readers who want to gain a greater understanding of the broad outline of human evolution and how researchers are attempting to unravel it. Zimmer has done a fine job of hitting on the main points, explaining the underlying concepts, and inserting just enough detail about new techniques or controversies to engage the reader's attention.