sign in sign up
<<
Home , Cladogram, Willi Hennig

"Cladistic Analysis or Cladistic Classification?": A Reply to

Willi Hennig

Systematic , Vol. 24, No. 2. (Jun., 1975), pp. 244-256.

Stable URL: http://links.jstor.org/sici?sici=0039-7989%28197506%2924%3A2%3C244%3A%22AOCCA%3E2.0.CO%3B2-3

Systematic Zoology is currently published by Society of Systematic Biologists.

Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use.

Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/journals/ssbiol.html.

Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission.

JSTOR is an independent not-for-profit organization dedicated to and preserving a digital archive of scholarly journals. For more information regarding JSTOR, please contact [email protected].

http://www.jstor.org Sun Apr 15 18:23:03 2007

POINTS OF VIEW 245

entific theory with that of a schedule, or question of what animal system is the format, of taxonomic activity. I doubt, best, I don't believe that it can be posed therefore, if Mayr's "evolutionary system- so generally (as Giinther has pointed out, atics" is really based on scientific theory- "the system of cook books is the best for a doubt that has been expressed often, the purpose of a cook book). For the perhaps most clearly by Johnson (1970), scientifically best system, Mayr, neverthe- who is himself an advocate of "evolutionary less, states several criteria, among which the ." best "explanatory, predictive, and heuristic Mayr's epistemological imprecision stands properties7' (p. 94) and an "efficient in- out clearly in his desire to build his "evolu- formation storage and retrieval system7' (p. tionary" system in a "synthetic7' (p. 95) 94) may be the most important. But I manner according to two different view- raise a question about the significance of points: phylogenetic and, also, adaptioge- the concept of "prediction," which seems to netic ( ecofunctional) . With this system, me a purely formal and meaningless meta- built according to two different viewpoints, phor, adopted by Mayr from a special group a user can never know of a particular group of biological theories to which no theory (taxon) if it is based and defined phy- of biological systematics belongs. Indeed, logenetically or adaptiogenetically (eco- the concept of predictions plays no further functionally). This circumstance, contrary role in Mayr's presentation-except to fig- to Mayr's belief, reduces the information ure in some very general assertions ("The content of his "evolutionary" system (see number of evolutionary statements and below). predictions that can be made for many The logical demand for strict uniformity holophyletic groups . . . [that is, the mono- of viewpoint in the arrangement of systems phyletic groups of phylogenetic system- (already established although not always atics] is often quite minimal" [p. 961). followed by Aristotle), is neither mentioned And it seems to me that Mayr, contrary nor refuted by Mayr. He would, perhaps, to his stated purpose, agrees with my reject this demand as formalistic, for he opinion of the logical priority of the phylo- elsewhere rejects other logical demands. genetic system: "The synthetic or evolu- But rejecting a logical demand is not in tionary method of classification . . . agrees itself a valid scientific refutation, and is with in the postulate that as com- at best a reckless practice--even outside plete as possible a reconstruction of phy- the sciences. logeny must precede the construction of a classification" (p. 95) and "Hennig is quite right when he states: 'phylogenetic re- I will now consider the particular ob- search as biological science is possible only jections enumerated above, with which if it adopts the discovery of the genealogical Mayr contests the scientific permissibility relation of as its first objective' " (p. of phylogenetic systematics. 97). "The cladists are sincerely convinced that Here I draw attention to a distinction their theory produces the best classifica- that might be made between the concept of tions" (p. 96). This assertion, with which system and that of classification. Let me Mayr introduces his refutation of this al- begin with an example. If an archaeologist leged claim of the "cladists," is false, as discovers potsherds in a tomb, he might is evident by examination of Mayr's cita- begin by ordering, or classifying, them in tion ( Hennig, 1971) : I have maintained some way: according to their material only that the phylogenetic system, as a (clay or metal), their color, their decora- general reference system, has a certain tions, etc. Subsequently, he might attempt logical priority; and this statement is not to reconstruct the original vessels (vases, the same as Mayr's assertion. As for the urns, etc.), of which the potsherds are SYSTEMATIC ZOOLOGY fragments. This reconstruction is another fute the "cladists." It is a type of argument kind of ordering. One might call it a that he uses also in other places in his paper. system, but one need not call it a classifica- In actuality, the conversion of a clado- tion. For another example, I refer to the gram into a hierarchical system is possible rivers of Europe. These may be classified without a single additional assumption or according to their navigability, water man- the redefinition of any of the concepts used agement, the conditions they offer for the in constructing the . The con- settling of organisms, etc. But one might version is a purely formal operation. Given seek to determine the drainage (Danube, the cladogram of Mayr's Fig. la, for ex- Rhine, Elbe, etc.) to which each belongs, ample, the following hierarchy results: in order to construct a different kind of system of rivers. Similarly, the construc- Taxon (B + C + D) tion of a cladogram in accordance with I. Taxon B the principles of phylogenetic systematics 11. Taxon (C + D) results in a system rather different in prin- 1. Taxon C ciple from various kinds of possible classifi- 2. Taxon D cations. Although my original perception Why I often prefer a hierarchical system of this distinction was somewhat unclear, to a cladogram also needs brief discussion I have nevertheless avoided speaking of (sections &7). phylogenetic "classification," preferring in- stead phylogenetic "system"-but I have 4. sometimes used "classification" under the influence of English usage. The logical priority of the phylogenetic A peculiar defect in Mayr's work, one system, as a general reference system, arises which jeopardizes the whole of what he from its foundation in a biological theory presents a fundamental contribution, is that with unambiguously defined central con- he disputes (p. 100) the conversion of a cepts. Mayr, however, objects to what cladogram into a hierarchical system: "As he terms "arbitrary decisions, involving a valuable as the cladistic analysis is, it does redefinition of well known terms" (p. 100) not automatically provide a classification" and I respond as follows: (p. 123), and "The basic postulate of the cladistic theory, a complete congruence of a. , a term coined by Haeckel a cladogram and classification, can be satis- more than 100 years ago, has never before fied only by making numerous assumptions been unambiguously defined. The Greek and redefinitions and by ignoring numerous word roughly means origin of phyla (groups facts of and phylogeny (broadly of common descent). According to evolu- defined)" (p. 100). tionary theory, phyla originate by succes- These assertions are simply false. They sive cleavage events within organismic would be correct if "classification sew communities of reproduction. Phylogenetic Mayr" were inserted in the two sentences systematics defines phylogenesis in this un- ambiguous sense. Mayr considers this in place of "classification." Then, neither definition erroneous, and adds, as a second Mayr nor I would dispute their truth. Mayr "set of factors" the "amount and nature of here confuses the aims of "cladists" with evolutionary change between branching those of "evolutionists" (with respect to points" (p. 95). But these companion phe- the construction of systems), although he nomena of phylogenesis, which vary more previously described correctly the differ- or less in different sister-groups, are dis- ences between the two. And he reproaches cussed in the literature under the terms the "cladists" because they proceed dif- adaptiogenesis and anagenesis (or aramor- ferently than he wishes. Through this re- phosis ), about which, however, there is markable solipsism, Mayr presumes to re- some ambiguity of meaning. Because he POINTS OF VIEW 247

senses, perhaps, that these are logically traditional definition, that a group is "mono- secondary epiphenomena of phylogenesis, phyletic" if its members have a common Mayr calls his recommended theory of sys- ancestor, is recognized by Mayr himself, tematics "evolutionary" rather than phylo- who adds the qualification that "the com- genetic. ponent species, owing to their characteris- tics, are believed to be each other's nearest b. Relationship is a term that in English as relatives" (p. 104). But the value of his well as German means either form rela- addition is annulled by the ambiguity of tionship or genealogical ( blood) relation- the term "nearest relatives." If one under- ship. Mayr defends this ambiguity even stands "nearest relatives" in the genealogi- for the practice of biological systematics, cal sense (rather than the form sense), thereby disregarding the need for unam- then the only difference between Mayr's biguously defined terms and precise con- definition and that of phylogenetic system- cepts. Thus, it seems to me that Mayr's atics is their relative clarity of formulation. position is logically indefensible: one can- At the present time, some systematists not work logically with ambiguous terms, wish to use the tern1 "monophyletic" to the meaning of which is not determinable refer to groups that I termed paraphyletic. in any given case of usage. Phylogenetic Mayr cites Ashlock, who introduced the systematics defines the term relationship term holophyletic for groups that are mono- unambiguously as genealogical (blood) re- phyletic in the phylogenetic sense (groups lationship. But "unambiguous7'describes an whose members have an ancestor in com- attitude that Mayr dismisses as "highly mon only to themselves). Ashlock wished specialized" (p. 102); and Mayr's dismissal to use the term "monophyletic" in referring places his argument beyond the realm of both to holophyletic and paraphyletic reasonable discussion. groups. A typical paraphyletic group is that of "animals" in a classification con- c. , as treated by Mayr, shows trasting man and "animals"; another is how much he engenders confusion rather "" in a classification contrasting than clarity by his disregard of the need and "invertebrates." To term for unambiguous definitions of scientific such groups ("animals" and "invertebrates") terms. Mayr, on his part, defends the "monophyletic" merely renders the term "traditional definition" of (p. 99) of mono- useless. Ashlock's attempts (1)to associate phyly and asserts that I have caused much paraphyletic and holophyletic (monophy- confusion by defining the term precisely. letic) groups under a common definition In actuality, the "traditional definition" of (Ashlock's "monophyletic"), and (2) to monophyly, as Mayr understands it (de- contrast them with "polyphyletic" groups, scent from a common ancestor), is meaning- on the basis of certain supposed similarities less. When Mayr asserts that "groups that and differences in the structure of genea- are not composed of descendants of a corn- logical relationships, I expect on theoretical mon ancestor are artificial and of low pre- grounds will founder hopelessly. dictive values7' (p. 95), this assertion is A categorical distinction exists between itself meaningless: any two species what- monophyletic groups (Ashlock's holophy- ever are descendants from a common letic), whose members possess a stem spe- ancestor (according to this "traditional cies common only to themselves, and non- definition," any group whatever is "mono- monophyletic groups (paraphyletic and phyletic" ). The definition becomes clear and usable only when the additional state- polyphyletic), whose members always pos- ment is added that species of a mono- sess a common stem species but not one phyletic group have an ancestor (stem common only to themselves. species) in common only to themselves. A distinction between the terms para- To some extent, the vagueness of the phyletic and polyphyletic is possible only SYSTEMATIC ZOOLOGY

polyphyletic particular kind of mistake made in the group process of character analysis that led to the formation of the groups. From this paraphyletic standpoint, the terms paraphyletic and poly- group phyletic are not used for indicating dif- ferences in the genealogical relationships between taxa (groups). In view of the con- fusion already caused by Ashlock, and the acceptance of his suggestions by Mayr and Weidner, terminological clarity can best be preserved by rejecting Ashlock's compro- mise, and accepting the concept of mono- phyly as defined by phylogenetic system- atics. For the moment, however, one could, perhaps, speak of monophyletic (holophy- letic) groups. Contrary to Mayr's assertion, the defini- tion of the concept of monophyly does not first become important during the con- version of a cladogram into a hierarchic FIG. 1.-Polyphyletic and paraphyletic groups. system, but rather during the construction Species A, C, E agree in primitive (plesiomor- phous) characters; species B, D, F in derived, of the cladogram (during "cladistic anal- but convergently evolved characters. ysis," i.e., the determination of the chrono- logical sequence of branching points and the relative recency of common ancestry). at the methodological level. For example, A "cladogram" that does not explicitly an investigator may discover that a certain indicate the monophyletic (holophyletic) monophyletic group had previously been groups, is no cladogram of the phylogenetic subdivided into two or more non-mono- system. If Mayr does not understand this phyletic subgroups. If so, the investigator aspect of , then I would con- mav determine that one of two ~ossible sider specious his appreciative remarks errors had been committed (fin. 1): a about the value of "cladistic analysis": his subgroup may have been forheud oi the assertion, "There is little argument between basis of convergence (such groups have cladists and evolutionary taxonomists about customarily been termed polyphyletic); or the cladogram" (p. 98), would be un- a subnrou~mav have been formed on the - A tenable. basis of symplesiomorphic agreement (such groups have sometimes been termed "poly- 5. phyletic,"-. sometimes "monophyletic"). Both types of groups, those based-on convergence "Neglect of the dual nature of evolu- (what I consider polyphyletic groups) and tionary change" (p. 105). Mayr states that those based on symplesiomorphy (para- I have "created enormous confusion" (p. phyletic groups), are similar, for the mem- 104) with my unambiguous definition of bers of each group-type lack a stem species monophyly, which, Mayr asserts, "ignores, common only to themselves. As the figure indeed it quite deliberately conceals, the shows for groups of either type, there need most interesting aspect of evolution and be no difference between them in the struc- phylogeny" (p. 104), namely that of radia- ture of their genealogical relationships. The tive and divergent adaptiogenesis. This terminological distinction between paraphy- definition, of course, is the basis for groups letic and polyphyletic groups is valid, there- such as Archosauromorpha, which include fore, only when attention is drawn to the and (as well as various POINTS OF VIEW 249 fossil groups related to them). Mayr con- siders this particular group "useless" (p. 104). But in my opinion information about the possible amount of adaptiogenetic di- vergence of sister-groups is here even better expressed than in the usual classifications, particularly those that do not indicate even that crocodiles and birds are sister-groups: e.g., Class Reptilia (Order Crocodylia, Order . . ., Order . . .,), Class Aves. With his criterion ("neglect of the dual nature of evolutionary change"), Mayr would have reason to reject groups such as Chordata, which include divergent adaptiogeneses (e.g., Tunicata and Aves ), and Mammalia, which also include diver- gent adaptiogeneses (e.g., Monotremata and Proboscidea). Reflections along these lines, which could be continued indefi- nitely, demonstrate that Mayr's weak and vague conceptual constructs are scientifi- cally ineffective because of their ambiguity. Of Mayr's arguments, there remains only the unfounded assertion that "To give them [e.g., crocodiles and birds] the same cate- gorical rank . . . may be logically im- peccable, but is simply wrong biologically" (p. 122). Here, as elsewhere, "Mayr be- takes himself beneath his level in his polemic against ph~logeneticsystematics" ( Lother, 1972:237).

"Evolutionary systematics," as pro- pounded by Mayr, also makes use of a FIG.2.-Phylogeny of Sauropsida according to hierarchic system. For construction of recent authors. The phylogenetic relationships of this system, Mayr considers, besides the Testudines are unclear. branching sequence of phylogeny, a second "set of factors" (or "variables" [p. 9-51 ), namely the "amount and nature of evolu- I. Testudines tionary change between branching points." 11. Archosauromorpha And Mayr contends that the system of A. Crocodylia "evolutionary systematics" consequently has B. Aves a much higher information content than 111. Lepidosauria that of phylogenetic systematics. Let us A. B. Squamata now check if this contention is true. Ac- cording to current publications, the phy- The information content of this hierarchy logeny of recent Sauropsida is as shown arises from its absolutely reliable reflection in Figure 2, which may be converted to of the known branching sequence of the a hierarchy thus: cladogram; the branching sequence can be SYSTEMATIC ZOOLOGY retrieved from the hierarchy just as ac- curately as from the cladogram. In addi- tion, the hierarchy also indicates the un- certain interrelationships of the major groups ( Chelonia, Archosauromorpha, Lep- idosauria). For example, if the chelonians prove to be the sister-group of the re- maining Sauropsida, the hierarchy, of course, could be modified to express this new information: I. Testudines 11. Sauropsida sew strict0 A. Archosauromorpha 1. Crocodylia 2. Aves B. Lepidosauria 1. Rhynchocephalia 2. Squamata The "evolutionary" system of the Sau- ropsida has never been specified by Mayr, but let us assume that it is similar to the system commonly found in textbooks: Class Reptilia 1. Order Chelonia 2. Order Rynchocephalia 3. Order Squamata 4. Order Crocodylia Class Aves If we wish to rewrite this hierarchy as a cladogram, it would appear as in Figure

3. This "cladonram,"- , of course, is false, as shown by comparison with the original (Fig. 2). I conclude, therefore, that the FIG.3.-"Cladogram" resulting from the attempt "evolutionary" system of the Sauropsida to reconstruct a "" from the "evolutionary" classification of Sauropsida into mav contain little or no information about classes and orders. the branching sequence of the original cladogram-even though Mayr asserts that this first "set . . . of factors: phylogenetic If the "evolutionary" system contains no branching" (p. 95) is, or should be, con- reliable information about the first "set of tained in the system. For other groups the factors" that it allegedly contains, what "cladogram" that might be rewritten from then is the status of the second "set of an "evolutionary" system, according to the factors" ("amount and nature of evolu- same principles and without adding in- tionary change between branching points")? formation, would correctly represent part According to Mayr, this second set of factors of the branching sequence of the original is extraordinarily complex. It includes, for cladogram; but without additional informa- example, even the "role a higher taxon tion we could not identify the part correctly plays in the economy of nature" (p. 122). represented. But here I would ask, what objective stan- POINTS OF VIEW

dard, actually or potentially binding on all systematists, may be used to convert these many things of the highest qualitative di- versity into a quantitative value (for this is what is involved in the last resort), thereby to determine the coordination and subordination of groups in the "evolution- ary" system? This standard of measurement is nowhere to be found in the literature, not even in Mayr's works. Mayr does not give us even the rudiments of a praticable and teachable method (there is, of course, an extensive literature on this issue, but I will not pursue it further here). If one asks wherein the "amount and nature of evolutionary change" is truly ex- pressed, then the answer can be only in terms of the "amount and nature" of the manifold differences of the most diverse kinds that occur between organisms. If we wish to introduce into a hierarchic sys- tem information about the nature and amount of these differences, then we are concerned not with the process of phylo- genesis and evolution, but with the results of that process (see above: adaptiogenesis as an epiphenomenon of phylogenesis). If we wish to build a hierarchical system with FIG. 4A.-The phylogenetic system of . this result, then it becomes irrelevant if the The hierarchical division of subgroups is derived result was ~roducedthrough phylogenesis from the branching sequence of the phylogenetic (evolution) or through a sudden act of tree (the tree can be reconstructed from the creation. Mayr must sense this because hierarchical system). he repeatedly appeals to Aristotle, and A. Entognatha reproaches phylogenetic systematics for I. Ellipura a. Protura adopting "Aristotle's downward classifica- b. Collembola tion" (p. 105). But I think that Aristotle, 11. Diplura even if equipped with our present knowl- B. Ectognatha edge of the differences (in the broadest I. Archaeognatha 11. Dicondylia sense) among organisms-but without a. Zygentoma knowledge of the processes of phylogene- b. Pterygota sis-would have to reach the same results as Mayr and his adherents: according to the estimation of "amount and nature" of totelean" (Crowson, 1970) or "typological" these differences. And Aristotle, too, would systematics. Discussion about the relative merits of not have any binding objective standard of phylogenetic and Aristotelean systems are measurement for assessing differences of presently hampered and confused by two Gestalt. The term "evolutionary system- circumstances. The first circumstance is atics" is, therefore, misleading, and I think that the principles of phylogenetic system- Mayr's system is better termed "Aris- atics are frequently illustrated by reference 252 SYSTEMATIC ZOOLOGY

FIG. 4B.-Classification of insects (after Grass&, 1949, in Traitd de Zoologie). FIG. 4C.-Classification of insects (after, Weber, 1954, in Grundriss der Insektenkunde). 1-5, "Sub- I. Apterygota classes." A. Entotropha 1. Protura 1. Collembola 2. Collembola 2. Protura 3. Diplura 3. Diplura B. Ectotropha 4. Thysanura 1. Archaeognatha 5. Pterygota 2. Zygentoma 11. Pterygota transcending any reasonable purpose, to to Amniota or Sauropsida. These illustra- neglect these facts in a hierarchical system. tions are convenient, because everyone has But let us note that the group Archosauro- an intuitive concept associated with the morpha is not at all "useless" (p. 104), names of the groups, but use of as Mayr asserts. But it is all too easy to these illustrations has certain disadvantages. argue with a single extreme case. Fig. For example, to conclude that the group 4A-E shows some of the systems proposed "Reptilia" must be dissolved and that for insects in various texts and handbooks. crocodiles and birds must be associated in They are similar in attempting to represent one group (Archosauromorpha) of the phy- in a hierarchy the morphological divergence logenetic system strikes many as shocking of groups, the "amount and nature of evolu- and absurd: for the "amount and nature tionary change," or "magnitude of anage- of evolutionary change" (or, as others have netic steps." Their differences arise from said, the "magnitude of anagenetic steps") the different ways in which the different appears to separate birds so distinctly from authors evaluate these phenomena (see all "reptiles" (including crocodiles) that it length of arrows; it may be remarked here seems pure formalism, and perfectionism that the system in fig. 4E is not false in POINTS OF VIEW 253

FIG. 4D.-Classification of insects (after Beier, FIG. 4E.-Classification of insects (after Renner, 1969, Handbuch der Zoologic). SbCI, subclass; 1971, in Zoologisches Praktikum). a, b, unranked SpO, superorder; 0, order; SbO, suborder. groups; SbC1, subclass. I. SbCl Entognatha a. Entotropha A. SpO Collembola 1. SbCl Diplura B. SpO Diplura 2. SbCl Protura 1. 0 Diplura [sic] 3. SbCl Collembola 2. 0 Protura b. Ectotropha 11. SbCl Ectognatha 4. SbCl Archaeognatha 0 Thysanura 5. SbCl Zygentoma 1. SbO Machilinea 6. SbCl Pterygota 2. SbO Lepismatinea 111. SbCl Pterygota Indeed, if in the history of systematics there has been a certain progress in the the sense of phylogenetic systematics, but direction of a generally accepted system only incomplete: it omits some of the (at least for some groups), this is the information about relationships of particu- gradual progress toward a phylogenetic lar groups). Similar examples could be system. cited for most animal groups. And as long The second circumstance that engenders as there is no objective and generally confusion can likewise be recognized from binding standard of measurement, by which Fig. 4A-E. In the Aristotelean system, just we may measure the "amount and nature as in the phylogenetic system, the limits of of evolutionary change" or "magnitude of the groups (taxa) always coincide with anagenetic steps," and thereby demonstrate branching points of the cladogram. It re- that one of the proposed systems is more quires little thought to perceive why this correct than the others, there can and will must be so. Accordingly, we can establish, be no generally accepted Aristotelean even for a system that originated before the ( "evolutionary") system. theory of descent, that the limit of a group SYSTEMATIC ZOOLOGY

always coincides with one or another distributional notes. But a phylogenetic branching point of the cladogram-insofar system can be augmented through such as we know it today. The difference be- notes and thereby serve as a source of in- tween a svstem that originated before the formation more easily, I think, than an theory of' descent, andvone built in ac- Aristotelean system, which is determined cordance with Mayr's recommended prin- already in its construction by an obscure ciples, consists only of our knowledge that combination of qualitatively different view- the differences between scroups arose in the points. On this matter, too, I will only - A course of a phylogenetic process (in con- hint here at further considerations. nection with cleavage of species). But if Mayr asserts that phylogenetic system- Mayr's principles are followed, this addi- atics is impractical because there are some- tional knowledge is without any significance times not enough characters available to for the theory and methods of biological determine the interrelationships of all the systematics: the differences between birds species of a particular group. This is true. and crocodiles, and the differences between Therein lies, however, a stimulus for further crocodiles and other "reptile" groups, re- study. Indeed, unresolved problems of re- main the same-equally great or small, lationship, uncovered by phylogenetic sys- equally significant or insignificant in any tematics, have already led to successful conceivable respect-regardless if ( 1) we goal-oriented studies (e.g., by Schlee, regard the differences as the results of a Zwick, et al.). sudden act of creation, or (2) recognize The reason why phylogenetic systematics them as conseauences of the fact that is not satisfied merely with a cladogram in the course of phylogenesis different in the sense of Mayr, to represent the results branches of the phylogenetic tree prove of of studies in branching sequence in a par- different significance for the origin of pres- ticular group, but prefers a hierarchical ent discontinuities in the form- and life- system, may be made clear with one final diversity of organisms. We thus return to consideration. A hierarchical system has the conclusion already reached that the many advantages. It can be clearly set out term "evolutionary" system is misleading, in a small space; for the birds, for example, and that there is no fundamental distinction it would take up the same space as Wet- between an "evolutionary" system and a more's checklist. It would allow anyone pre-Darwinian, or Aristotelean, system. quickly and clearly to recognize the gaps With the demonstration (Fig. 1) that in our knowledge: species of unknown in- there is no distinction between paraphyletic terrelationships could be listed in alpha- and polyphyletic groups with respect to the betical order under their appropriate genealogical relationships of their compo- monophyletic group; groups of doubtful nents, it also becomes illogical to argue monophyly could be placed in brackets or that an "evolutionary" system differs from indicated with question marks (these, of a me-Darwinian svstem in the elimination course, are purely technical devices). But L of polyphyletic groups from the pre-Dar- we should consider the value of this sys- winian. tem, in the simple form of a checklist, as (1)an information source and (2) a stimu- lus for studying yet unresolved branching sequences of the phylogenetic tree. Can So far we have considered systems in a "traditional," or Aristotelean, system, built the form of simple hierarchies. Further according to Mayr's recommendations, have information could be introduced by textual the same value as an information store and exposition at the various hierarchical levels as a stimulus for new studies? I am afraid of either a phylogenetic or Aristotelean sys- that a catalogue of the 300,000 species of tem. Such textual exposition is normally , even if it could be constructed on included, for example, in checklists with the principles of Mayr's recommended POINTS OF VIEW

Aristotelean system, would in practice be case represent the same taxon, irrespective an information source only for those of whether or not the Miocene species and coleopterists who constructed it. its Recent descendants belong to the same community of reproduction and are thus conspecific in the sense of the biological Apart from his unsubstantiated critique species concept). Now because we know (1) of the fundamental questions discussed that in Recent species subpopulations that above, which Mayr believes adequate to originated only a relatively short time ago refute phylogenetic systematics, he also differ slightly from one another, and be- critically treats at length some questions cause (2) that morphological distinctions of secondary importance for his theme. between different Recent species can often Only some of these will be discussed here. be determined only with difficulty (Dro- For example, he reproaches me for "a purely sophila, Phlebotornus), we may assume that formalistic species definition" (p. 109) and in most if not all cases the Recent descen- refers to a note on the deviation rule given dants of a particular species from the geo- by Schlee (1971:28). Hitherto I have as- logical past will be slightly different, sumed that the biological species concept, irrespective of whether they today form used by me since 1950, does not essentially one species or many species. The deviation differ from that of Mayr (Hennig, 1950, rule and the illustrative figure with which 1966). The concept is, of course, based on we are here concerned (Hennig, 1950: study of Recent species. But if one believes fig. 25) are, therefore, not false in this that, despite all difficulties and restrictions sense. The presentation by Schlee, which in particular cases (of which we are well Mayr criticizes so vehemently, has no other aware), the Recent species of any complete purpose than to show this. Not only Mayr's checklist conform to the biological species critique, but also the conclusion of Peters, concept, then this should be the case also upon which Mayr bestows much approval, for any species known for example from completely miss this point. Miocene fossils (naturally, it is impossible in practice to set out a complete checklist of this kind, including both fossil and Recent Mayr considers, also, if we should speak species, but it must be admitted as a con- of the persistence of a "stem species A" ceptual possibility). Three and only three alongside a daughter "species C" (pp. 109- possible genealogical relationships are con- 110) during the cleavage of an ancestral ceivable between, for example, the Miocene species. Phylogenetic systematics prefers to and Recent species of a monophyletic accept the daughter species, B and C, as group: (1) A Miocene species has no given, and to consider the stem-species (A) descendants in the Recent fauna; (2) A that gave rise to both. Mayr does not note Miocene species has one descendant species that his consideration is in reality a dispute in the Recent fauna; (3)A Miocene species about words (neither he nor anyone else has two or more descendant species in the knows the gene-pool of any stem-species Recent fauna. In case (2),it is possible that before and after its cleavage). So we deal the Recent (descendant) species either does here simply with different descriptions of or does not differ in recognizable characters the process and results of speciation; that from the Miocene species. For neither of the "cladists" is methodologically better possibility could it be decided if the Mio- ( Giinther, 1962:279). cene and Recent specimens belong to the Mayr attempts to invalidate the "cladistic same or different biological species (this is principle of dichotomy," noting that phy- of no importance if we are*interested only logenetic cleavages may conceivably occur in the genealogical relationships in a par- also in a multiple or radiative manner. But ticular context; for the specimens in either in refutation of this objection, also raised by SYSTEMATIC ZOOLOGY

Darlington, other authors have already "evolutionary systematics" in no case is argued that, even when a strictly dichoto- spared the incidental difficulties of phylo- mous branching of the phylogenetic tree genetic systematics, which Mayr so em- cannot be demonstrated, an investigator phatically draws to our attention. Mayr's need never conclude that multiple specia- criticisms of phylogenetic systematics there- tion has in fact occurred (although it might foxe seem to me unsound. His indisputably have). Mayr (p. 110) takes notice of, but great achievements lie in another field. does not seem to understand, this refutation. Moreover, the principle that every mono- ACKNOWLEDGMENTS phyletic group has only one sister-group, I have had much trouble in convincing myself although not strictly verifiable empirically, that I have neither misunderstood nor unjustifiably has a high heuristic value: it challenges criticized Mayr's exposition. In this regard I am the investigator to study carefully every grateful to Prof. K. Gunther, Berlin, for carefully reading, criticizing, and in important points ex- case where no dichotomy has yet been panding the draft of my rebuttal. Thanks for the demonstrated. same services are due, also, to Dr. D. Schlee, Ludwigsburg.

Mayr's section entitled "The mode of REFERENCES origin of higher taxa" (pp. 111-113) is CROWSON,R. A. 1970. Classification and biology. based on confusion of the "cladistic ap- Heinemann Educational Books, London. G~~NTHER,K. 1962. Systematik und Stammes- proach with that of "evolutionary system- geschichte der Tiere 1954-1959. Fortschr. Zool. atics," and inspires Mayr, as the final 14:268-547. proof of his error, to reproach the "cladists" HENNIG,W. 1950. Grundzuge einer Theorie der with the "phyletic tree" drawn by 'rhrock- phylogenetischen Systematik. Deutcher Zentral- morton (1965) for the Drosophilinae (Mayr's verlag, Berlin. HENNIG,W. 1966. Phylogenetic systematics. Uni- fig. 5). This "phyletic tree" is formed ac- versity of Illinois Press, Urbana. cording to the principles of "evolutionary HENNIG,W. 1969. Die Stammesgeschichte der systematics" and is therefore a proof of Insekten. Waldemar Kramer, Frankfurt/M. the conclusion (see above) that a tree-like HENNIG,W. 1971. Zue Situation der biologischen Systematik. Erlanger Forsch. 4B:7-15. drawing not founded on the concepts JOHNSON,L. A. S. 1970. Rainbow's end: the quest (monophyly, relationship) defined by phy- for an optimal .. Syst.. Zool. 19:203- logenetic systematics is not a cladogram of 239. the phylogenetic system. Hence, Mayr's LOTHER,R. 1972. Die Beherrschung der Man- argument on this point is epistemological nigfaltigkeit. Gustav Fischer, Jena. MAYR,E. 1974. Cladistic analysis or cladistic nonsense. Besides, I doubt that even Mayr, classification. Z. Zool. Syst. Evo1.-forsch. 12: much less Throckmorton, would argue that 95-128. the species Drosophila tripunctata, standing SCHLEE,D. 1971. Die Rekonstruktion der Phy- at the apex of this "phyletic tree," is really logenese mit Hennig's Prinzip. Aufsatze Red. the stem species of all other taxa shown Senck. Naturf. Gesell. 20: 1-62. THROCKMORTON,L. 1965. Similarity versus rela- there, as Mayr's "evolutionary systematics" tionship in D~osophila. Syst. Zool. 14:221-245. implies. Many of Mayr's remaining sections con- tain questions about the modus operandi Staatliches Museum fur Naturkunde of the "cladists," and are answered in the in Stuttgart works of the various representatives of phy- 714 Ludwigsburg, Arsenalplatz 3 logenetic systematics. Moreover, Mayr's Federal Republic of