Principles of Systematic Zoology, 2nd Edition. STOR Review Author[s]: Kevin de Queiroz

Systematic Biology, Volume 41, Issue 2 (Jun., 1992), 264-266.

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http://www.j stor.org/ Mon Mar 11 14:09:12 2002 Reviews

Syst. Biol. 41(2):264-266, 1992

Principles of Systematic Zoology, 2nd edition.•Ernst ing species concepts (p. xix), but that does not excuse Mayr and Peter D. Ashlock. 1991. McGraw-Hill, their failure to mention one concept that has received New York, xx + 475 pp. $39.95 (cloth). considerable attention in the recent systematic liter- ature, namely, the phylogenetic species concept (e.g., In 1969, Mayr's Principles of Systematic Zoology was Cracraft, 1987; Mishler and Brandon, 1987; Nixon and probably the best systematic text and reference book Wheeler, 1990). If nothing else, phylogenetic per- available (Michener, 1969), and it retained a promi- spectives on the species problem have drawn atten- nent place among such works for years after its pub- tion to the fact that interbreeding is not the only lication. When first published, it was current, au- interesting phenomenon that occurs at the microtax- thoritative, and comprehensive, and even more than onomic level (de Queiroz and Donoghue, 1988). 20 years after its heyday I continue to use my copy Mayr and Ashlock also dismiss too hastily Pater- frequently. Although several excellent books on the son's (e.g., 1985) critique of the biological species con- subject have been published subsequently, only Wi- cept. Paterson called for replacement of what he views ley's (1981) Phylogenetics serves as many different pur- as the traditional version of that concept, which he poses. But a lot has happened since 1969. No book calls the isolation concept, with an alternative that about systematics published that long ago is current emphasizes mate recognition instead of reproductive today. Consequently, the publication of a revised edi- isolation. He has attempted to discredit the biological tion of Principles of Systematic Zoology raises hopes of species concept because of a supposed tie to the con- a new standard for the field. cept of reinforcement, the idea that characters re- The new edition has been reorganized and, com- sponsible for the absence of interbreeding between pared with its predecessor, places greater emphasis the organisms of different species ("isolating mech- on concepts and theory. It consists of 14 chapters, the anisms") have evolved as a result of selection against first of which is an introduction to the science of hybrids. In Mayr and Ashlock's defense, even if Pater- taxonomy, including a brief history and a discussion son is correct in concluding that reinforcement is un- of the role of taxonomy in biology. The remaining 13 important in the evolution of intrinsic reproductive chapters are divided among three major sections. The barriers, the biological species concept need not be first two of these sections, which were devoted to replaced. Regardless of historical associations be- principles and methods in the first edition, are now tween the concepts of biological species and rein- devoted to "Microtaxonomy," dealing with species forcement, the two are not tied logically to one an- and infraspecific categories, and "Macrotaxonomy," other. As a general species concept based on dealing with higher taxa. The last major section, titled interbreeding, the biological species concept can be "Methodological Issues," covers issues relating to sys- adopted regardless of whether intrinsic reproductive tematic collections, taxonomic publications, and the barriers result from reinforcement or, as Paterson be- rules of zoological nomenclature. Also included are lieves, they are by-products of the adaptation of mate a glossary, a bibliography, and a combined subject recognition systems to different environments. and author index. The volume is reasonably well pro- Nevertheless, other aspects of Paterson's critique duced, with only a moderate number of typographical deserve consideration. For example, according to Mayr errors, and its size is comfortable in the hand. and Ashlock, the term "species is a relational term like The section on microtaxonomy covers a diversity the word brother" (p. 39). This proposition implies of topics, including species concepts, the ontology of that it is nonsensical to speak, even hypothetically, species, infraspecific categories, population structure, of the existence of only a single species. In contrast, different kinds of variation within species, methods Paterson's emphasis on recognition, rather than iso- for comparing population samples, and speciation. lation, led him to reject the idea that the term "spe- Given Mayr's prior writings on species, it is not sur- cies" is relational (e.g., Paterson, 1984). Paterson's po- prising to find strong advocacy for the biological spe- sition is more congruent with the view, endorsed by cies concept. I was, however, surprised to find logical Mayr and Ashlock themselves (p. 40), that species are inconsistencies reflecting incomplete acceptance of "individuals" (composite wholes). Organisms form that concept. For example, Mayr and Ashlock seem composite wholes called populations as a result of unable to decide whether asexual organisms form interbreeding with one another, not as a result of species (p. 32), and at one point they suggest that avoiding interbreeding with the organisms of other reproductively separate entities that are not distinct populations. in other respects should not be recognized as separate The section on macrotaxonomy consists of chapters species (p. 93). The authors admit their bias concern- devoted to general principles, taxonomic characters. 264 1992 REVIEWS 265

phenetics, cladistics, evolutionary classification, and names) were seen to be composite wholes•albeit of numerical methods of phylogeny inference. Mayr and different kinds (populations and clades)•rather than Ashlock favor evolutionary classification over phe- classes based on shared organismal characters. And netics and cladistics, which is to be expected, but their in each case, the new concept of taxa brought a new bias becomes too great when they define certain gen- theoretical context to comparative biology (popula- eral terms, such as "biological classification" and "tax- tion thinking and tree thinking) (O'Hara, 1988). From on," in a way that precludes the alternative approach- the viewpoint of developing a phylogenetic system es. In any case, the chapters devoted to alternative of taxonomy, the changes involving the higher taxa macrotaxonomic approaches reveal much, both stated are particularly important in that they grant the con- and unstated, about how Mayr and Ashlock perceive cept of evolution a more important role in taxonomy. the alternatives. The chapters on phenetics and cla- No longer are taxa based on shared characters and distics are largely critiques. Unfortunately, Mayr and only interpreted after the fact as having been pro- Ashlock's characterizations of those approaches are duced by evolution; evolution is now fundamental inaccurate or outdated. For example, they attribute to to the very concept of taxa (de Queiroz, 1988). pheneticists the claim that grouping according to sim- Although Mayr and Ashlock have made the con- ilarity will automatically produce a phylogenetic clas- ceptual shift with regard to species, they have not yet sification, and they continue to characterize the cla- done so for higher taxa. For example, they continue distic approach to classification as being concerned to view higher taxa explicitly as classes (p. 113). They only with the branching component of phylogeny. view the entire endeavor of macrotaxonomy as a Regardless of these problems, the discussion of phe- problem of how best to classify organisms "according netics receives only 11 pages, whereas cladistics gets to their similarities" (p. 115), rather than a question of 36. Furthermore, the chapter on evolutionary classi- inferring which organisms or species are descended fication (32 pages) is devoted in a large part to con- from a particular common ancestor. For Mayr and tinuing the argument against cladistics. Mayr and Ashlock, macrotaxonomy is a two-step process (p. 243). Ashlock apparently perceive cladistics as posing a In the first step, species are sorted into relatively ho- serious threat to their preferred approach. mogeneous groups that reflect their overall similarity. The arrangement of the book into sections devoted Only after taxa have been formed according to this to microtaxonomy and macrotaxonomy is supposed nonevolutionary criterion are they tested for consis- to reflect the insight "that taxonomy at the species tency with evolution, that is, for monophyly in the level is very different from taxonomy at the level of broad sense. Thus, in Mayr and Ashlock's approach higher taxa" (p. xviii). Although a difference certainly to macrotaxonomy, taxa are based on similarity, and exists, the way in which the difference is conceptu- evolution is granted only a relatively weak kind of alized by Mayr and Ashlock stems from their view "veto power." Calling this approach "evolutionary of macrotaxonomy, which is currently being replaced. classification" is misleading because it is not the ap- Mayr's conservative stand on this issue is ironic, for proach that grants the most important role to the in many ways the view that he so vigorously resists concept of evolution. is the macrotaxonomic counterpart of a microtaxo- The third section is titled "Methodological Issues," nomic perspective championed by Mayr himself. An but such issues are also discussed in both of the pre- important part of what came to be known as the New vious sections. The section on microtaxonomy covers Systematics, of which Mayr was one of the principal a variety of simple methods, but several more com- architects, involved replacing the view that species plicated ones are neglected, including some that are are groups of similar organisms with the view that currently in wide use. Ordination techniques, such species are populations•entities that result from in- as principal component analysis and multidimen- terbreeding. Analogously, what has come to be known sional scaling, are only mentioned, and other recently as cladistic classification, which Mayr and Ashlock developed methods for the analysis of geographic persistently oppose, consists largely of replacing the variation (e.g., Sokal, 1983) are not mentioned at all. view that higher taxa are groups of similar organisms In the section on macrotaxonomy, the chapter on with the view that higher taxa are clades•entities methods of phylogeny inference is better, possibly as resulting from common descent. a result of its having been "completely revised by The parallels between these two developments are David Maddison" (p. xx). The assortment of authors, striking. In each case, the definition of a taxonomic however, makes for a heterogeneous presentation, term ("species" and "monophyletic taxon") was re- combining straightforward descriptions of methods formulated so that it would refer to a class of entities with digressions on matters such as use of the term resulting from a particular biological process (inter- "character" versus "signifer." breeding and common descent). In each case, sup- The chapters in the third section are in some ways posedly homogeneous taxa that had been recognized the most useful in the book, partly because they cover by earlier workers (morphospecies composed of sep- topics lacking in most other books on systematics. arate interbreeding units and homogeneous but para- Compared with the preceding chapters, they also ex- phyletic higher taxa) were rejected if they did not fit hibit a high ratio of information to disputation, and the new definitions; correspondingly, heterogeneous despite the title of the section, at least the chapter on taxa that might not have been recognized by previous nomenclature contains a good deal about principles. workers (polymorphic species and heterogeneous Here Mayr and Ashlock discuss topics often taken for monophyletic taxa) were accepted if they fit the new granted or otherwise neglected, such as the impor- definitions. In each case, taxa (those entities given tance and workings of collections, different kinds of 266 SYSTEMATIC BIOLOGY VOL. 41 taxonomic publications, and principles of nomencla- PATERSON, H. E. H. 1985. The recognition concept ture. Although some of the practical matters covered of species. Pages 21-29 in Species and speciation (E. seem out of place in a book on the principles of sys- S. Vrba, ed.). Transvaal Museum, Pretoria. tematics (e.g., how to prepare a manuscript for pub- SoKAL, R. R. 1983. Analyzing character variation in lication), even these will be appreciated by the be- geographic space. Pages 384-403 in Numerical tax- ginning student. onomy (J. Felsenstein, ed.). Springer-Verlag, Berlin. The literature references are both a strength and a WILEY, E. O. 1981. Phylogenetics. John Wiley, New weakness of the book. The bibliography is extensive York. (30 pages), although the text citations vary from thor- Kevin de Queiroz, Division of Amphibians and Reptiles, ough to less than adequate, depending on the subject. National Museum of Natural History, Smithsonian Insti- Mayr and Ashlock deliberately did not replace some tution, Washington, D.C. 20560, USA. of the literature cited in the 1969 edition with newer references "to prevent excellent older papers from being forgotten" (p. xix-xx). Including newer refer- ences does not, of course, necessitate the replacement Sysl. Biol. 4U2):266-267, 1992 of older ones, but in many cases newer references were not added. Mayr and Ashlock's book has major strengths and Sex and Death in Protozoa. The History of an Ob- weaknesses. The broad range of topics covered and session.•Graham Bell. 1988. Cambridge Univer- the general organization are things that an instructor sity Press, New York. 199 pp. $47.95 (cloth). looks for in a textbook for use in an introductory course on systematic biology. However, to cover cer- Sex, as imagined by most biologists, is a reproduc- tain important topics even minimally, the text would tive process that begins with recombination and re- have to be supplemented by additional readings. Giv- duction during meiosis and gametogenesis, wanders en the exciting developments in macrotaxonomy that through the vagaries of mating, and concludes with have occurred during the last 20 years, Mayr and syngamy, restitution of the genome, and the produc- Ashlock's conservative position on this topic gives tion of offspring. Yet, strictly speaking, sex need only the book an anachronistic character; this is perhaps involve the exchange of genetic material between its most disappointing feature from the perspective individuals; as such, it seems to be an essential fact of potential use as a textbook. As a reference book, of life for nearly all species. Even so minimally con- its broad scope and extensive bibliography are assets, strued, sex appears to be genetically and demograph- but coverage of certain topics and recent literature ically an expensive proposition with respect to asex- could have been better. Times change, and so must uality, hence explaining its persistence has been new editions of books if they are to regain their place termed "the queen of problems in evolutionary bi- of prominence. Although the second edition of Prin- ology" (Bell, 1982). ciples of Systematic Zoology is useful both as a textbook In his first book on the evolution of sex, Graham and a reference, I doubt that its importance will come Bell (1982) began the task of unraveling the compo- close to matching that of the first edition. nents, consequences, and functions of sex, largely in R. J. O'Hara and K. I. Warheit provided valuable the context of metazoans. He primarily sought an comments on a draft of this review. ecological scenario that would give individuals that engage in sexual reproduction a sufficient selective REFERENCES advantage over those engaged in asexual propagation CRACRAFT, J. 1987. Species concepts and the ontol- to overcome (or at least balance) the genetic and de- ogy of evolution. Biol. Phil. 2:329-346. mographic costs of sex. His conclusion, one that re- DEQUEIROZ, K. 1988. Systematics and the Darwinian mains favored (but is by no means a consensus), is Revolution. Phil. Sei. 55:238-259. that spatial or temporal variation in selective regimes DE QUEIROZ, K., AND M. J. DONOGHUE. 1988. Phy- can produce the necessary advantage over ecological logenetic systematics and the species problem. Cla- time. distics 4:317-338. In Sex and Death in Protozoa, Bell remains true to the MAYR, E. 1969. Principles of systematic zoology. Mc- challenge of understanding how sex is maintained Graw-Hill, New York. (rather than how it originated) but shifts his attack MicHENER, C. D. 1969. Review of Principles of Sys- on the problem in two important respects. First, rath- tematic Zoology, by E. Mayr. Syst. Zool. 18:232-234. er than seeking an explanation that suffices at the MiSHLER, B. D., AND R. N. BRANDON. 1987. Individ- level of the individual and in ecological time, he con- uality, pluralism, and the phylogenetic species con- siders higher levels of selection over longer time spans cept. Biol. Phil. 2:397-414. to explain the prevalence of sex. Second, he focuses NIXON, K. C, AND Q. D. WHEELER. 1990. An ampli- on ciliate protozoans, in which sex is generally unen- fication of the phylogenetic species concept. Cla- cumbered by recombination, gametogenesis, and re- distics 6:211-223. production; rather, there is only a reciprocal exchange O'HARA, R. J. 1988. Homage to Clio, or, toward an of some genetic material (the micronucleus) between historical philosophy for evolutionary biology. Syst. partners, a process termed conjugation. The micro- Zool. 37:142-155. nucleus itself is not somatically active; it primarily PATERSON, H. E. H. 1984. The recognition concept directs the course of replication of the macronucleus, of species. South Afr. J. Sei. 80:312-318. which in turn regulates vegetative function. From