Book Review: Evolutionary

The Evolutionary Biology of Plants Niklas, Karl J., 1997. ISBN 0-226-58083-0 (paper $19.95) xix + 449 pp. University of Chicago Press, 11030 South Langley Avenue, Chicago IL 60628
- Plant biologists will enjoy this stimulating book, but there may be reservations about its use for students. Clearly it is towards students that it is directed because of its very affordable price in paperback. Karl Niklas is well known for his efforts to bring plant biomechanics into the forefront of botany (Plant Biomechanics and Plant Allometry) and there is much of this engineering approach to biology in the book under review. However, here he attempts a much more ambitious program, no less than a description of evolutionary diversification in plants, from the origin of life itself to the diversification of modern plant groups. Botanists will welcome his consistent choice of plants to exemplify evolutionary concepts and he makes no apologies for reiterating basic principles from a "phytocentric bias" because of his belief, correct I am sure, that students learn best by repetition. His constant emphasis on why plants, for developmental reasons, may differ from animals in their evolutionary processes becomes an important message. The underlying approach is that of "adaptive evolution," based on the Sewall Wright metaphor of the "fitness landscape," a landscape including "adaptive peaks" up which genotypes and phenotypes may be driven by natural selection. The book is liberally sprinkled with computer simulated "adaptive walks" in such hypothetical landscapes or "morphospaces." The refreshingly unique approach in this adaptationist program lies in the consistent attempt, not merely to describe, but to try and account for plant biological processes and their structural bases in functionally adaptive terms. For example, it is not sufficient simply to describe the biochemistry of the photosynthetic mechanism, rather there is a discussion of its probably origins in terms of microbial evolution. Similar approaches govern basic evolutionary events like the origins of the eukaryotic condition, sexual reproduction, multicellularity, the advent of a land flora through to the functional basis for evolutionary diversification of plants in terrestrial floras. In all, eight major evolutionary events in the evolution of plants are discussed. A veritable tour de force.

The book is divided into four sections, each with two chapters, so the chapters are long. The first section covers basic evolutionary principles and speciation and may seem dated in terms of some of the examples used. However, the opportunity to see older work presented in a newer context is stimulating and such a background may be deemed necessary to understand later discussion. The second section is highly contemporary in its chronicle of evolutionary events from the perspective of cellular processes and cell origins, but continues through to the diversification of modern plant groups. It provides as concise and lucid an overview of the origin of plants and their life cycles as one could wish - from the primordial ooze to the flower in a hundred pages. The third section is entertaining because of its more speculative nature, exploring the condition under which plants first diversified in water to their landward migration in functional terms, making liberal use of the adaptationist philosophy. The final section brings us into the domain that Niklas has made very much his own - the adaptive radiation of more recent groups of plants in functional or mechanical terms, providing an opportunity to demonstrate divergences and convergences in the diversification of the land flora. The final chapter is a rather disconnected return to evolutionary principles and a brief outline of molecular genetics. In summary, this is an ideas book that attempts much, but since the writing carries one along with the continual presentation of new approaches, the result is stimulating and enjoyable.

Reservations about the book arise from the method of illustration and the "adaptationist" program itself. Illustrations are almost universally derived from computer-generated images ("cartoons" the author called them) so this is a book about plants without illustrations of plants. The result is a good way to present ideas, but can produce little more than caricatures of real organisms (virtual botany?) and it is not difficult to point out error. It is a botany based on hypothetical models, and known information is either ignored, misunderstood or misinterpreted because sources are either not cited or are often secondary. This detracts from the pedagogic botanical process of showing what plants actually look like. The text would well be supplemented by a laboratory course so that one can more directly appreciate the substrate for all these ideas. For a text-book, the rapid presentation of so many ideas may be a good challenge to more advanced students.

The adaptationist program itself offers difficulties that Niklas himself is careful to point out in the introduction - how does one know that natural selection is indeed working on the structures emphasized and in the ways proposed? For example, it is an attractive idea to interpret ovule morphology in early seed plants in terms of pollen capture, but how does one know it is true? The distinction between plausible explanation and precise mechanism, especially in fossil groups, is a grey area and students should not be led into the mist blindfold. The concept that these are hypothetical presentations, initially stated, is soon abandoned, even though the word "posited" is liberally used. The transition from speculation to conventional wisdom is readily made in the absence of experimental verification, or extensive biological comparison. Due caution is necessary and the author's own view of naive expectancy on the part of an observer should at all times be borne in mind.

The balance sheet is still overwhelmingly in favor of a strong recommendation. The book comes at an appropriate time in the intellectual development of evolutionary biology since its constant emphasis on how organisms work and how evolution is a continual modification of functional processes is a welcome antidote to the current myopic view of many biologists that evolutionary study is simply the identification of putative phyletic lineages and organisms exist only to be reduced to character states and characters. There should be balance in intellectual endeavors and this book could represent a point at which biology might be directed back to the study of organisms at work. The notion that a "grade" level of comparison is as important as a "clade" level analysis has almost been lost from our botanical classrooms. Niklas here provides a medium in which the products of evolutionary innovation can be assessed in likely functional terms.

The book is well produced and errors are minor (although any paleobotanist knows that Zosterophyllum is not a seagrass!). I recommend this work as a major contribution to the understanding of the evolutionary biology of plants. - P. B. Tomlinson, Harvard University, Harvard Forest, Petersham, MA 01366.

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