Classified information

In this third edition of Five Kingdoms Lynn Margulis and Karlene Schwartz propose a new and comprehensive classification system for all organisms known to western science. Reconciling often conflicting evidence from a range of sources - from traditional fossil-based to recent molecular data - the authors have managed to synthesise a phenomenal range of biochemical, morphological and behavioural information into a mere 520 pages. The book thus represents the culmination of a clearly daunting task.

The introduction gives a brief overview of the nature and history of biological classification and provides tips on how to use the book. Each of the following chapters then gives an equally brief summary of the relevant kingdom and provides short descriptions of its component phyla.

Rejecting the molecular-based three-domain system of classification proposed in 1990 by microbiologist Carl Woese, the authors favour the system of five kingdoms (plants, animals, fungi, protoctists and bacteria) first proposed by Robert Whittaker in 1959. These five kingdoms are further grouped into the superkingdoms Prokarya and Eukarya. Here, the superkingdom Prokarya is composed of the single kingdom Bacteria, which in turn is divided into the two subkingdoms, Archaea (two phyla) and Eubacteria (12 phyla) on the basis of molecular differences in their ribosomal DNA. The superkingdom Eukarya contains the kingdoms Protoctista (30 phyla), Animalia (37 phyla), Fungi (three phyla) and Plantae (12 phyla).

Each chapter begins with a phylogeny, tracing the evolutionary relationships believed to exist between component phyla. A general introduction to the kingdom is then followed by a description of some of the biochemical, morphological or reproductive characters used as the basis for each phylum's classification. These sections include diagrams and/or photographs of representative organisms, and often include points of interest such as the use of organisms within human society.

Throughout the text, the arbitrary and dynamic nature of scientific classification of biological diversity is regularly emphasised, the authors acknowledging that "only the species is a natural taxon" - though even this view might be argued on the basis of recent research into contemporary folk taxonomies. This type of open discussion should prove invaluable in preparing biology undergraduates for the conflicting taxonomies they are likely to encounter during their studies.

The book's brief section on field trips focuses largely on the United States and a number of exhibitions, research centres and natural history museums are suggested. More globally applicable is the list of internet resources at the end.

While the book claims to be suitable for students of biology at any level - including "curious naturalists" and "armchair explorers" - the text will be most valuable to younger undergraduates as a general introduction to taxonomic issues.

Overall, there is no doubt that the classification system proposed in Five Kingdoms offers a valuable contribution to modern discourse on biological classification, particularly since it draws together so much disparate information.

Cath Cotton was a senior lecturer in biological sciences, Roehampton Institute, London, and is currently based in Amsterdam with Greenpeace.