Happily, the inside of the book is for the most part as interesting and enjoyable as the outside. Hardly anyone can be more qualified to present an overview of biology than Mayr, a professor emeritus of zoology at Harvard and one of this century's leading contributors to evolutionary thought. His work on the evolutionary synthesis and mechanisms of speciation is, by consensus, an essential part of Darwinism circa 1997, and he has been honored with the top prizes in his field. He has also carved out a second career as a historian and philosopher of biology, most notably in two of his previous books, The Growth of Biological Thought: Diversity, Evolution, and Inheritance (1982) and Toward a New Philosophy of Biology: Observations of an Evolutionist (1988).

Mayr's latest offering, This Is Biology, is in large part a summary of his views on the theory and practice of the discipline to which he has devoted his professional life. The book can be roughly divided into thirds. The first few chapters deal with the big questions, including the definition of "life," the nature of science, and the ways in which science - and in particular biology - attempt to explain the living world. The middle section discusses four areas of the life sciences - biodiversity, developmental biology, evolution, and ecology - with descriptions of past successes and of unanswered questions. The book concludes with chapters on human evolution and on the potential for a moral and ethical framework grounded in an understanding of human biology and an evolutionary worldview.

The theme that binds these chapters together into a coherent, sustained argument is Mayr's insistence that the theory and practice of biology can be fully appreciated only by recognizing that what holds true for the physical sciences does not necessarily hold true for the life sciences. As he states in the preface:

Much of Mayr's understanding of the uniqueness of the biological sciences comes out of his own experience as an evolutionist. For example, the demise in biological thought of essentialism - defined by Mayr in his helpful glossary as "a belief that the variation of nature can be reduced to a limited number of basic classes, representing constant, sharply delimited types" - was a direct consequence of the Darwinian revolution. The recognition that each individual in a population is genetically unique is one of the indispensable principles of evolution by natural selection. Throughout the book Mayr insists that biology is so often misunderstood because so much of it is outside the bounds of "physicalist thinking," i.e., the conviction that all natural phenomena can be explained by the application of universal, immutable laws. The distinction between "population thinking" in evolutionary biology and the search for laws in the physical sciences is best made by Mayr in his explanation to the physicist Wolfgang Pauli: "He finally came close to understanding it when I suggested to him to think of a gas consisting of only 100 molecules, each differing from the others in direction and speed of movement."

Many of the other philosophical ideas or approaches that Mayr suggests inform biology - probability, chance, historical narratives - are also indebted to the rise of evolution. Obviously, establishing causality in such a field is a significant problem since the life history of a particular lineage is riddled with contingency: climate change, changes in the abundance of predators or prey, catastrophic impacts, random genetic mutation, and other events that cannot be recovered by science. Mayr makes the point that while one will probably search in vain for a law that explains the evolutionary history of a species, the combined efforts of paleontologists, ecologists, geologists, and molecular biologists can establish a sequence of events that in all likelihood contributed to significant developments in the history of life. This approach may have limited predictive power, but it suffices to explain the unique occurrences that are studied by biologists.

It is important to note, I think, that Mayr may be underestimating the power and influence of "biological thinking." After all, cosmologists, while dealing for the most part with physical laws, are establishing the ultimate historical narrative: the origin and development of the universe. In fact, physicist Lee Smolin's new book The Life of the Cosmos is an effort to explain our universe and the laws by which it is governed in Darwinian terms. Cognitive scientist Daniel Dennett has documented the potential impact of evolutionary thinking on a whole range of disciplines, terming natural selection "universal acid" in his recent book Darwin's Dangerous Idea. Whether or not Smolin and Dennett have taken a good idea too far remains to be seen, but it seems clear that biological concepts are very much in the forefront of contemporary thought.

Perhaps the most convincing and important of Mayr's principles of biological thought is pluralism. By this he simply means accepting the fact that many natural phenomena can be explained in more than one way. Some may require multiple explanations. This is best illustrated by his distinction between proximate causation (the domain of molecular and cellular biologists and physiologists) and ultimate causation (the domain of evolutionary biologists). A complete understanding of an appendage, for example, requires both proximate and ultimate explanations in order to describe both how it works and why it works the way it does. Mayr makes the compelling case that many debates in the history of biology have arisen because each camp was unconvinced of the importance of pluralism in the life sciences. He notes that contemporary developmental biology is in a unique position, explicitly combining "how?" and "why?" questions to explain embryonic development. To Mayr's credit, he also practices what he preaches, presenting his own arguments gently and with an appreciation for the complexity of the subject matter.

Biology, like many of the textbooks devoted to it, is a large and unwieldy subject. As good as This Is Biology is, one sometimes feels that each of the chapters works better on its own than in the context of the larger book, which quickly jumps from topic to topic. The opening chapter, "What Is the Meaning of 'Life'?" might be a perfect introduction to a course in undergraduate biology. Likewise, the chapter on developmental biology is a beautifully clear overview of the questions that developmental biologists are attempting to answer. Other chapters, such as "Does Science Advance?", seem less relevant and tend to interrupt the flow of the book. That said, This Is Biology is certainly worth the time of anyone interested in biology, professional or not. There are a lot of ideas presented here, and although they are not always easy to grasp, that too may be part of Mayr's point. Life, including the small, rich corner of it on the front cover, is anything but simple.

Harvard University Press - Site includes review quotes, table of contents, and links to other works by the author.

The World of Richard Dawkins - a good Web site on evolution, devoted to the work of this theorist but also with links to other evolutionary biologists, plus several discussions and reviews of all aspects of evolution. Of particular interest is societies "Evolution, Science, and Society," a comprehensive white paper on behalf of evolutionary biology written by representatives of various biological societies.

The World Wide Web Virtual Library: Evolution (Biosciences) - an equally good evolution page, including links to relevant books, software, newsgroups, journals, university departments, summaries of meetings, and natural history museums. Of note is the home page for Harvard's Museum of Comparative Zoology, Ernst Mayr's professional home for much of his career. This site also includes a link to the Ernst Mayr Library at the museum, named in his honor.

The talk.origins Archive: Evolution and Philosophy: Reductionism and Evolution - a summary of reductionist arguments and counterarguments in biology. Ernst Mayr has a lot to say about reductionism, arguing that since organisms exhibit "emergent" properties at higher levels of organization, a reductionist (i.e., molecular) approach is not always appropriate.

"What is a Species, and What is Not" - article by Mayr analyzing " a number of widespread misconceptions concerning species." From the June 1996 issue of Philosophy of Science.

Freedom's Nest - this Web site, devoted to "peace and prosperity, free minds and free markets," has a brief Ernst Mayr page with links to quotes and available books.