Evolution of the Insects

David Grimaldi, and Michael S. Engel
Cambridge University Press, Cambridge, UK
2005, 755 pp.
Price: $75.00, hardcover
ISBN: 10 0-521-82149-5

While the recent publication of History of Insects by Rasnitsyn and Quicke (2002, Kluwer Academic Publishers, Dordrecht) represents a large compilation of information on insect fossils, no up-to-date comprehensive critical integration of fossil and extant insect diversity has been available. Certainly, that recent text contributed considerable (and valuable) coverage of otherwise nearly inaccessible literature about insect fossils and their deposits, but it did not attempt to treat extant insect diversity and relationships. As Grimaldi and Engel point out in their Evolution of the Insects, this lack of synthesis has left a huge gap in the literature that has made the teaching of insect diversity and evolution courses a complex task.

As an instructor of a course in insect classification and evolution, I have eagerly awaited the publication of Grimaldi and Engel’s volume as an important supplementary text for my students. Overall, my wait has been richly rewarded.

This is a beautifully produced book, with cleanly presented (often color) photos of fossils supplemented by attractively produced photos of living taxa, elegant line drawings, diagrams, and tables. The comprehensive compilation of the broad range of insect diversity across fossil and extant taxa is a Herculean task. Moreover, the authors have produced a highly readable and engaging text that should provide strong incentive for students to learn more. Anyone who does not enjoy browsing through or reading this book is not likely to be an entomologist!

(Hint: Buy the hardback version, which, although heavy, is reasonably priced; you will want to keep this one.)

The book begins with a general introduction to insect diversity and evolution and includes sections on species and their diversification, the history of insect systematics, and the contribution of systematic and paleontological knowledge to our reconstruction of insect history. The introductory chapter is followed by a description of the different forms and biases of insect fossilization, fossil-dating procedures, and the major fossil deposits through time and space. Chapter 2 should, in my opinion, be essential reading for entomology students, especially those who focus on insect ecology or systematics.

Most of the book is a fascinating march through the relationships of insects to other arthropods and an evolutionary sweep through the insect groups extinct and extant. The latter is enhanced by the authors’ persistent efforts to integrate biology with classification and provides countless images and references that are useful for teachers and students alike. In the penultimate chapter, they discuss the dramatic diversification of insects and angiosperms during the Cretaceous and Tertiary. The book concludes with a return to the question of how many insect species there are, and what the future might hold for insect diversification and extinction.

The volume does, however, possess some annoying idiosyncrasies that could easily be minimized in future editions. The authors’ commendable and balanced effort to integrate current systematics with a long history of paleoentomology is distorted at times by an overzealous promotion of the strict cladistic perspective.

Although a strong phylogenetic perspective is essential to this work, a total dependence on parsimony-based analytical methods and a marked preference for citing works based upon them is not. A particularly striking example of this is the discussion of systematics and evolution in Chapter 1, where the authors conflate distance methods with phenetics and advance the claim that establishment of homology is more broadly established with morphological characters than with molecular (particularly DNA sequence) data. Surely the reverse is typically true with the use of nuclear protein-encoding genes, which are now widely used for phylogeny estimation. Grimaldi and Engel (perhaps understandably, given their backgrounds) place a much heavier emphasis on the difficulties associated with analysis of molecular data than on the equally daunting challenges with interpretation of comparative morphology—probably because of their mistrust of the evolutionary models that are central to most maximum likelihood and Bayesian analyses of sequence data.

Although this review is perhaps not a suitable place to fully debate the pros and cons of competing systematic methodologies, neither is a textbook on the history of insects. It would require little effort for the authors to update Chapter 1 to reflect more accurately the diversity and advances in analytical rigor of current molecular systematic approaches and enhance the readers’ understanding of the issues.

In general, the authors go to great lengths throughout the book to present a balanced view of prominent controversies in phylogeny and classification. Good examples include their conclusions that the placements of the enigmatic Strepsiptera and recently described Mantophasmatodea are uncertain. Even though their treatment of arthropod relationships favors the (earlier, but now minority) view that hexapods are more closely related to Myriapoda than to Crustacea, they lucidly present both sides of the argument without attempting to represent these relationships as being settled. Yet their discussion of arthropod relationships omits reference to the recent comparative developmental literature, which has done much to clarify our understanding of limb and segment homologies.

There are, however, occasional exceptions to the trend of balanced representation, when the authors prematurely take sides in unresolved controversies. In the treatment of bee relationships in Chapter 11, for example, they inaccurately state that the sister-group relationship of stingless bees and bumble bees inferred from several early molecular studies "has not held up to scrutiny against larger, more comprehensive studies." In reality, a body of recent literature (not cited in the book, but published in prominent journals) has not only presented much additional molecular evidence for this relationship (the six genes analyzed to date by several lab groups are entirely congruent in this respect), but recent and more comprehensive combined analyses have also supported it. The controversy nevertheless remains because all molecular data support a relationship in conflict with the majority of comparative morphological (and some behavioral) interpretations. The corbiculate bee relationships would thus be best treated as uncertain. Students would then be encouraged to contribute more data and analysis to a still-fascinating question central to the understanding of the evolution of social behavior in bees.

Fortunately, lapses in objectivity and scholarship are rare in this broad text, and it would be too much to expect complete accuracy and absence of personal perspective in a work so comprehensive and so obviously close to the authors’ hearts. The book is undoubtedly more of a success at integrating paleoentomology with current comparative morphological views than with current molecular phylogenetic progress; it nevertheless stands as a remarkable attempt to present the broad sweep of extant and extinct insect diversity in a detailed yet easily accessible fashion.

There will still be a need for advanced classes to provide students with current literature to produce a full picture of the most current understanding of insect phylogeny, but Evolution of the Insects will be an invaluable supplementary resource for insect classification and evolution courses for the foreseeable future. Its spectacular production will no doubt serve the broader reading public as a positive advertisement for and introduction to the fascination entomologists feel for insects.

The authors and Cambridge University Press are to be congratulated for making this large volume such a pleasure to read and use. I took the book with me to read on vacation and didn’t once wish I had taken something else!