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COMPARATIVE BIOLOGY: FORM, TIME and SPACE (1: Systematicsand Biogeography;Cladistics and Vicarianceby Gareth Nelson and Norman Platnick

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COMPARATIVE BIOLOGY: FORM, TIME and SPACE (1: Systematicsand Biogeography;Cladistics and Vicarianceby Gareth Nelson and Norman Platnick COMPARATIVE BIOLOGY: FORM, TIME AND SPACE (1: Systematicsand Biogeography;Cladistics and Vicarianceby Gareth Nelson and Norman Platnick. Columbia University Press, New York, 1981. xi + 567 p. $ 35.00.) Progressing from the maxim that earth and life have evolved together, and taking their organizing principle from the title of a book by CROizaT (1964) Space, Time, Form: The BiologicalSynthesis, Gareth Nelson and Norman Platnick introduce the prob- lematic of their book-an inquiry into the theoretical structure of comparative biology and the nature of our knowledge of organismic diversity. Their treatise opens with an introductory chapter of some 50 + pages, providing the reader with what is essentially an extended precis of the book's contents. Comparative biology is resolved into the elements of Croizat's "alternative threefold parallelism" - Form, Time and Space-and selected subdisciplines-systematics, embryology, paleontology and biogeography---are introduced. This first chapter explores in a nov- el and entertaining way the problems posed by pattern analysis in the three realms, and outlines the methodological tools adopted for their resolution. Like much of the rest of the book, it is clearly written, with problems interestingly formulated and concepts simply, if sometimes controversially, outlined. For example, in a discussion of "kinds" of organisms (species and groups-it is with the latter that the book is centrally concerned) the "species problem" is neatly dispatched and, for the authors' purposes, the sufficient concept of species as "simply the smallest detected samples of self-perpetuating organisms that have unique sets of characterrs" is provided (page 12). The remaining 480 pages are subdivided into seven chapters mirroring the structure of the introduction: FORM-systematichistory (chapt. 2), systematic pattern (chapt. 3), systematic results (chapt. 4), TIME-ontogeny,phylogeny, paleontology and the bio- genetic law (chapt.5), sPa.cE-biogeographic history (chapt. 6) biogeographic pattern (chapt. 7), biogeographic results (chapt. 8). As is perhaps to be expected, the historical considerations (basically chapters 2 and 6) pose least in the way of controversy-they are however, well-written and informa- tive. In their reassessment of the fields of systematics and biogeography Nelson and Platnick recognise in their own results the older notions of pre-evolutionary scientists - of "natural groups" (taxa) and of "natural areas" (regions). In stressing that "Sys- tematics and biogeography are sciences rich in past accomplishments" the authors' are keen to acknowledge a historical imperative and the historical perspective adopted lends insight into the ideas presented in the book. It is pleasing to find two champions of the contributions of Hennig and Croizat stressing an intellectual precedent in the earlier works of Rosa, Mitchell and A.-P. de Candolle, to mention but a few. Turning to more recent history and in a novel treatment of the phyletic versus phenetic versus gradistic controversy, various approaches to the "stability problem" of classification are outlined. The key to the general solution of the problem is located in Hennig's type of branching diagrams (page 142), and there follows a clear expo- sition of what is essentially the transformation of "traditional" phyletic-cladistics into a method of greater generality-a general method of taxonomy. The heuristic distinction between phyletictrees-depicting "aspects of evolutionary genealogies", and cladogramsdepicting "structural elements of knowledge" intro- duced in the first chapter is elaborated. From the statement "taxa A and B are related by common ancestry" two parts are extracted: "taxa A and B are related" (the clad- istic part), and "by common ancestry" (the phyletic part). The decoupling of the cladistic from the phyletic (or phenetic, or gradistic, or whatever) renders a branching 587 diagram illustrating an unspecified relation between certain specified terms (which may be taxa, areas of endemism, or even ethnographic artifacts). This decoupling provides a necessary separation if the pattern of relationship specified by cladistic analy- sis is to provide an adequate test of predictions derived from any particular theory of process.It is perhaps the recognition, and subsequent application, of the generality of the cladistic method and the distinction made between cladograms and phyletic trees, that distinguishes this book and its authors. But what of the important relation "synapomorphy"? Hennig defined synapomor- phy as "shared derived character", Nelson and Platnick take the abstraction further and explore is as a "subset". "Homology implies generality (that there is a set that includes ...), and synapomorphy implies relative, or restricted, generality (that there is a subset included in ...)" (page 158). Viewed in this way both homology and synapomorphy emerge as concepts which may be considered without reference to evolutionary theory-thus the numerous successful homology statements of the pre- evolutionary systematists. An illuminating discussion of homology in this vein is pre- sented in PATTERSON(1982). It is in that paper incidentally, we learn that Nelson's influential and much cited manuscript (Cladograms and trees, 1976) is now published as part of the book under review. Interesting also in this context, is the fact that although many of the ideas in the book are also to be found (often verbatim) in previous publications of both authors, there is no reference to this whole body of their work. It is no exageration to say that much of the book is about branching diagrams; their application and meaning in comparative biology. Regarding such diagrams as variously successful integrations of information. Nelson's method of "component analysis" emerges as a "general calculus" applicable to the examination of any branching diagram. The method is elaborated in considerable, one might almost say excruciating, detail in relation to systematics in chapters 3 and 4, and biogeographic analysis in chapter 7. Restricted to the practicably manageable analysis of basic 3- taxon (or 3-area) problems-more complex problems are reduceable to a series of 3-term statements-component analysis is essentially a means of revealing the infor- mation content of competing diagrams and classifications. Elaborated by the intro- duction of the concept the "general cladogram" (page 314), the method provides a criterion (the "cladistic parameter") for the selection of the most "efficient"-the most "informative" of competing diagrams. Once again, as there is "no necessary correlation between the cladistic parameter and any one discipline, such as phyletics, phenetics, or gradistics" (page 319), the generality of the method is stressed. What is being developed is a "theory of general cladograms"-a conceptual system with wide applicability. Chapter 5, intended as "a synthesis of the material preceeding it, with respect to the temporal dimension" is, in the authors' words "something of a digressionary in- terlude". Given the scope of a chapter subtitled-ontogeny, phylogeny, paleontology and the biogenetic law-it is not surprising that an attempted coverage in 21 pages (without a single branching diagram) is inadequate. Consideration of the temporal dimension of comparative biology is too scant rather than digressionary. Nonetheless the authors do raise some interesting propositions-it is a pity that they are not ela- borated in more detail or with more substance. Of Agassiz' threefold parallelism-ontogeny, phylogeny and paleontology-it is ontogeny that emerges as being of decisive importance. The orderliness of ontogeny - that the empirically observable transformations of ontogeny always seem to proceed from the general to the particular-is stressed, and comparative anatomy and paleontology are relegated to secondary disciplines ordering their data in conformity with the framework provided by ontogeny and its orderliness. .
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