SchuhR.T.: Biological Systematics: Principles and Systematics. Cornell University Press, Ithaca and London, 2000 236 pp., (cloth), 47.50 US$.ISBN 0-8014-3675-3.

There are not many up to date introductory books in phylogenetic systematics in English. ‘Cladistics’ by Kitching et al. (1998) is one, belonging to what may be labelled orthodox ‘pattern cladistics’. ‘Biological systematics’ by Schuh represents an excellent new addition for any student or other person looking for a general introduction to the field of systematics. ‘Pattern’ or not ‘pattern’ in Schuh's book is less obvious, suffice it to say that it is firmly rooted in parsimony and the writings of Farris (1979, 1983). It also has a wider scope than ‘Cladistics’ and could be viewed as follow-up of Wiley's (1981)‘Phylogenetics’.

The book is divided into the three main sections: Background for the study of systematics, Cladistic methods and Application of cladistic results. The Background section, apart from an introduction, goes through basic Linnaean nomenclature and philosophy of science. The nomenclatural part is well presented and addresses the five main issues: priority, availability, typification of species-, genus- and family-group taxa, homonymy, and synonymy, followed by a presentation of the Linnaean ranks, and a discussion on criticism of the system. A minor misconception includes a thought example of a nomenclatural system without types, where it is stated that the ‘choices would range from placing all species in a single genus, on one extreme, to describing a unique genus for each species, on the other’. But the types are irrelevant for the delineation of taxa, and this result could equally well be obtained under the current system! A discussion on phylogenetic nomenclature is postponed to the last book section (see below).

The philosophy of science gives a brief introduction to induction, to deduction, and to the hypothetico-deductive approach, including falsifiability and corroboration. It presents the by now classic Popperian view as introduced in cladistics by Farris, Kluge and others, and provides justification of parsimony and the role of ad hoc hypotheses. Parsimony has been criticized for making assumptions about evolution, but this criticism is rebutted; it bears no relationships to evolutionary models, but to finding optimal explanations for observations. Beware though, a series of talks (but unfortunately no publications yet) by Kirk Fitzhugh at, e.g. a series of Willi Hennig Society meetings, announce possible changes in the applicability of central issues such as ‘deduction’ and ‘tests’ in systematics.

The middle section on cladistic methods is the strongest part of the book which is clearly and well-presented. It starts with a presentation of the basic concepts of homology, apo- and plesiomorphy, mono-, para- and polyphyly, tree rooting by outgroup and ontogenetic data, ancestors and sister groups. Homology, as is well known, is an elusive concept. Schuh contrasts two views: (1) homology as topographical and structural similarity, and (2) homology equals synapomorphy. This section may be confusing to some readers, although this should probably be credited to the subject rather than to the presentation. Whereas Schuh applies the term in the first sense, I personally would see an advantage in abandoning such complex and ambiguous terms altogether. If homology equals similarity, then why not simply use the latter word? For assessment of synapomorphy in contrast, there is general consensus: congruence.

The explanations of mono-, para- and polyphyly include both Hennig's definition in terms of ancestor-descendants, and Farris’ (1974) operational definitions. The outgroup rooting largely follows the paper by Nixon and Carpenter (1993), and the discussion of ontogenetic data is largely based on Nelson's (1978) formulation of the biogenetic ‘law’: ‘Given an ontogenetic character transformation, from a character observed to be more general to a character observed to be less general, the more general character is primitive and the less general advanced’. Schuh's conclusion seems to be that the importance of ontogenetic data for polarity determination is debatable, and that they have their largest value in providing information for character state ordering.

The account for character coding gives no absolute indications, and the reader will not leave these pages with a clear-cut idea about how to score the observations. But indeed, there seems to be no easy answers around at present. In the example on appendages in tetrapods, dealing with multistate versus absence–presence coding, it is a bit unfortunate to include a character where both the state ‘anterior appendages absent’ and ‘anterior appendages lost’ are included, as the differentiation between the two kinds of absences is not based on direct observations but can only be made from congruence with other characters. The descriptions of quantitative methods include indices, optimization, tree searches and various weighting schemes. The explanations are brief but very clear and easy to follow. But in some instances Schuh is just too brief. Three-taxon statements are described in a few lines, and the criticism summarized as ‘it does not conform to the justification offered for parsimony because it does not minimize the number of ad hoc hypotheses of homoplasy, treating as independent quantities that are interrelated’. This may be clear to the reader who have read something previously on the subject, but unintelligible for the beginner. And the part ‘Rooting: additional discussion’ seems out of place (belongs to the previous section dealing with this subject), nor is the point very clear.

The third section deals with the application of cladistic results, and includes chapters on classification and databases, historical biogeography and host–parasite evolution, ecology and adaptation, and biodiversity and conservation. The biogeography and host–parasite sections briefly summarize the development and methodologies, including some current problems. This thing called adaptation (even more elusive than homology!) and its evaluation from trees, largely follows Coddington (1988). The biodiversity chapter gives an account of problems with regional diversity and the bias in our knowledge for diffferent areas, and very shortly introduces the relationship between cladograms and diversity. Although it is a bit odd to find the ‘surrogacy method’ (exchanging species counts for, e.g. families) under ‘Biogeographic information’, it is certainly welcome to see recommendations of caution in its application!

Cladistics is not exactly known to be a peaceful research area within biology, and there have been, and there still are, a series of highly controversial issues. These recur around the use of (standard) parsimony, distance methods, maximum likelihood and three-taxon statements, total evidence and consensus, Linnaean and phylogenetic nomenclature, to mention a few. When presenting these, Schuh attempts to give some space to all sides, but the arguments of the disfavoured sides are hardly given fair treatments. For the criticism of distance methods I can but agree, whereas for maximum likelihood I do not find the arguments very convincing, in spite of being a non-adherent. Schuh mentions lack of justification for choice of model, and inapplicability to morphological data. The latter is, of course, a (current?) restriction, but does not actually affect the justification. The main issue, in my view, is the question of models, and a more in-depth discussion on this would have been pertinent, instead of concentrating on unwarranted criticism of parsimony and (mis)understandings about long branch attraction. And the section on phylogenetic nomenclature (or taxonomy) is a caricature, where Schuh seems to be confounding taxa with the names of taxa. To be sure, the newcomer will certainly understand nothing about the differences between Linnaean and phylogenetic names.

In spite of these shortcomings, which I regard as minor, I like this book and recommend it to any beginners in systematics. Considering the ambitious scope, it is a pity that some parts are not treated a bit more extensively, and that a number of important issues are mentioned more or less en passant. The middle section ‘Cladistic methods’ stands out as the best part, with a very competent and easily followed treatment of character analysis, tree searches and tree evaluation. Finally, for those who care about book appearances (I do), it is a nice cloth binding that will survive many readings, and with a carefully chosen typography.