Function and Adaptation in Paleontology and Phylogenetics: Why Do We Omit Darwin?

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FUNCTION AND ADAPTATION IN PALEONTOLOGY AND PHYLOGENETICS: WHY DO WE OMIT DARWIN?

Frederick S. Szalay Departments of Anthropology, and Ecology and Evolutionary Biology, City University of New York; Hunter College, New York, New York 10021, USA; [email protected].

ABSTRACT

What phylogeny (but not classification) is has a bearing on how we should try to recover it. Phylogeny is descent with adaptive modifications constrained (and facilitated) by previous stages, largely through natural and sexual selection. This fundamental theorem of the evolutionary process contains a host of post-Darwinian advances in evolutionary biology that relate to it conceptually. Stated simply, this complex bundle of precepts is therefore the theoretical foundation of not only a Darwinian phylogenetic analysis, but also any comprehensive theory of function (in a broad sense) and of structure as well. Darwinian functional biology is also the study of adaptations and the process of their acquisition. Engineering assessments of features are not appropriate substitutes for Darwinian analysis. Fundamentally structuralist approaches to evolutionary analysis (including those of many phylogenists) consider the goals of adaptational analysis unattainable not only for fossils but for extant organisms as well. Yet adaptations in extinct species are often better understood than their phylogeny, in spite of widely advertised claims that phylogeny reconstruction is more properly scientific than adaptational analysis. Anyone work- ing with bone tissue, bones, joint complexes, and complete skeletal evidence who doubts that these levels are adapted both ontogenetically and phylogenetically either is unaware of the vast body of evidence that supports the adaptedness of the skeleton on all levels or chooses to ignore this area of knowledge in favor of the aesthetics offered by parsimony analysis. Both a strictly functional and an adaptational (ecologically utilitarian) assessment of traits is necessary, in both extant and extinct organisms, in order to reliably (i.e., probabilistically) establish polarities of homologous features that may be used in phylogenetic analysis. Such research, including the culling of homoplasies from a database, yields robust taxonomic properties against which lineage and taxon phylogeny hypotheses may be tested. The pairing of the “causal role function” approach of Lauder and co-authors with parsimony-based cladistics—which is a structuralist perspective, not a Darwinian one—does not advance the aim of reliability in phylogenetic reconstruction. Systematists should attempt to use only ordered and polarized characters in their probabilistic estimation of phylogenies, an approach that provides the most reliable assessment of phylogenetic hypotheses that can also have causal meaning. An evolutionary explanation (always constrained in its taxonomic expression by heuristics not directly relevant to phylogenetics) involves both the causal and historically mediated components of a particular transformation (an evolutionary becoming). A sharp theoretical distinction between functional and evolutionary explanations should

Szalay, F. 2000. Function and adaptation in paleontology and phylogenetics: why do we omit Darwin? Palaeontologia Electronica 3(2):25p, 366KB; http://palaeo-electronica.org/paleo/2000_2/darwin/issue2_00.htm F. S. Szalay: Function and Adaptation in Paleontology

be replaced by a less dichotomous and hierarchic, as well as a far more “temporally looped” and interrelated, conceptualization of the relationship between the evolution of the function (mechanics or physiology) and biological roles of features. Biostratigraphy and functional analysis (sensu lato) provide the theoretically valid bases of the transformational analysis of attributes of populations of organisms in phylogenetics. Trans- formational analysis of features should be biologically contextualized and kept independent of taxogram-driven parsimony analysis. Transformational analysis and the subsequent understanding of the relationships of lineages is a prerequisite for meaningfully tested taxon phylogenies. Both adaptational and phylogenetic analyses are inferential about events in the past and both are based on theoretical assumptions, never on complete evidential support; therefore neither has theoretical supremacy over the other. The widespread and dogmatically alleged primacy of parsimony-based cladistics as being the foundation of all phylogenetic considerations, with all its truncated and circular assumptions, is more a complex social construct (a Kuhnian paradigm) than a theoretically defensible position. KEY WORDS: Function, mechanical analysis, adaptational analysis, Darwinian phylogenetic analysis, parsimony cladistics, mosaic evolution. Copyright: Society of Vertebrate Paleontology, 15 November 2000. Submission: 6 July 1999, Acceptance: 29 August 2000.

INTRODUCTION entirely different from “siding.” Darwin sublimated both “structuralist” and “adaptationist (functional- Much has been written about the theoretical ist)” views of character equivalence into the corner- issues of functional biology, in a broad sense, as stone of the phylogenetic method, practiced in a these pertain to the study of living organisms, but variety of different forms since 1859. far less regarding the relevance and significance of As a consequence of the modern sidelining of function and adaptation for the historical under- the relevance of function to phylogenetic analysis standing of fossil and living animals. Furthermore, (and, even worse, a studied misunderstanding of although most ideas of function have always been 1 tied to adaptations (e.g., Pranger 1990), there has its role in phylogenetics ), there has been relatively also been a tacit general belief that adaptations (or little attention given to the connection between the adaptedness) of fossils cannot really be ascer- functional biology and transformational analysis to tained. Little attention has been paid to different phylogeny estimation in the past three decades of historical and systemic levels of adaptations within phylogenetics-related literature. Furthermore, judg- lineages and taxonomic species of these lineages ing from the masses of phylogenetic studies pub- beyond the taxic (and fundamentally punctuation- lished, most of what has been written in the ist) conceptualization (e.g., Gould and Vrba 1982). theoretical literature about function is either As a result, the usefulness of adaptational analysis ignored or misunderstood by most practitioners of and the applicability of ecological inferences for numerical cladistics, including stratocladistics. But phylogenetic analysis of both fossil and extant taxa the functional literature itself is often both equivocal has been all but ignored, if not explicitly berated. and confused regarding the role of functional biol- The philosopher Amundson (1996, p. 29), in ogy and its relationship to the estimation of phylog- his scholarly account of the history of ideas regard- eny. This is peculiar, because what phylogeny is ing adaptation, has stated that “Darwin sided with (as we understand it within well-tested Darwinian function.” To attribute “siding” to Darwin, however, theory) should have a bearing on the methods we given his elaborate presentation of the theory of use to reconstruct it. It is for this reason that I descent based on homology and the paleontologi- undertake the task of briefly drawing attention to cal record, is rather problematic. Such an opinion some theoretical and methodological relationships expresses a lack of familiarity with the corpus of (both ontological and epistemological) between Darwin’s work, and misconstrues Darwin, the mod- functional analysis (sensu lato) and phylogenetics ern phylogenist. For Darwin to reformulate the (but not the construction of taxograms or classifica- structuralist notions of his day into the theory of tions). First, I look at the general theoretical issues descent (evolutionary process) required something that relate to the estimation of adaptations in fossils

2 F. S. Szalay: Function and Adaptation in Paleontology and their phylogenetics. Second, I examine some complex of attributes that can yield these historical of the competing views of what functional biology is peculiarities (the phylogenetic signals) is likely to supposed to be in relation to functional and evolu- yield only ephemeral patterns, no matter how rigor- tionary analyses that include fossils. Third, I specif- ous the techniques (usually of fundamentally ically make connections between a broad concept flawed conceptual methods) are that are used to of functional biology and Darwinian phylogenetic arrive at them. It should be realized also that mac- analysis (but not the taxonomic expression of well- roevolutionary guesswork about paleontological tested phylogenies). Finally, I take a closer look at patterns that superimpose random walk models on issues surrounding transformational analysis and data do not in any way corroborate notions that attempt to refute arguments leveled against the certain segments of phylogeny were non-adaptive concept of mosaic evolution based on the taxic (contra Gould, 1988; Vrba, 1980). conceptualization of phylogeny. As a necessary preamble, it should be stated that each organism (a life history) is a complex BACKGROUND AND STATEMENT composite intertwined genetically (i.e., historically) OF THE PROBLEM and developmentally (in current and real time). [Note: In sexually reproducing organisms the ovum For those paleontologists (as well as neontol- itself also represents a critical component of the ogists) who study vertebrate skeletons, the spe- historical heritage beyond genetics.] The evolution- cies-specific microscopic as well as macroscopic ary fate of demes or species (not individuals, but attributes of bones are essential information. continua in time) is a consequence of the interplay These are the material foundations of their science of both the physical world and the Darwinian con- within the critical contexts of time and place. Bone text (the total environment), and the imperatives tissues and skeletons are complexly imbued, affecting the individuals that make up such evolu- because of descent and adaptation, with both the tionary units. The Darwinian components of tested constraints and adaptive meanings of their past evolutionary theory are obviously not only adapta- and present at any moment in geological time. This tion or adaptedness through natural selection and is realized differently at the levels between the modification through sexual selection, but also bone tissue, the intermediate trabecular structures, ancestrally constrained descent with modification. and the whole structure of a particular bone as part A combination of selectional “forces” (= causes) of a skeleton. Adaptive aspects of skeletal mor- drives the process of differential survival, and what phology are materially (albeit not conceptually) remains in terms of fitness (differential reproduc- 2 inseparable from their phylogenetic signals . Theo- tion) for each organism is its contribution to the retical perspectives that ignore contextual, inter- proportions of subsequent ontogenies (organisms). pretive, and functional analyses of such Modal patterns of the various frequencies of these complexes, and that are used subsequently to test variant ontogenies become fixed differently in pop- phylogenetic hypotheses, axiomatically deprive ulations or species, and these variably persist and themselves of a potentially enormous and relevant change in lineages. Therefore, phylogeny is a suc- material database. Such abiological and ahistorical cession of successful life histories (ontogenies in a views about data also potentially deprive phyloge- broad sense) in the context of ecology. The general netics of an organism-based causal explanation. statements in this paragraph are a set of assump- Science without causal explanations is a question- tions on which the issues discussed later depend. able enterprise. The specific issues examined in this paper are Contrary to such general notions that the con- concerned with neither evolutionary nor cladistic cept of adaptation is an onerous one (and should taxonomic expressions of phylogeny. The various be invoked only with great caution), the adaptive caricatures of these schools of classification have nature of bone tissues, bones, joints, and skeletal been discussed in the partisan literature. As stated systems have proven to be completely adapted by Padian (1999), Darwin’s concern was mainly within their phyletically constrained limits, both with the expression of phylogeny in formal classifi- ontogenetically and phylogenetically. This does not cations. But it is a mistake to ignore that it was mean that given this well-supported generality we already just as obvious to Darwin (as it is today) can easily understand this or simply accept gener- that phylogeny is both constrained and facilitated alities without rigorous research into the specifics by ancestry, which guides selectionally-mediated of such adaptations, but that phylogeny is the his- descent. Darwin also fully understood that all infor- tory of largely adaptive change, within the context mation was to be used to test phylogenies and that of historical peculiarities of all lineages. Attempting their taxonomic expression was fraught with the to decipher phylogeny without researching the compromises that such heuristic activity must face.

3 F. S. Szalay: Function and Adaptation in Paleontology

It is just as obvious now, as already noted, as it fossils, as independent of phylogeny as the con- was to Darwin that what this phylogeny is should cept of adaptation can be of phylogeny, is often direct the construction of methods, our epistemol- less of an epistemological problem than the ogy, in order to recover it.3 attempts at valid testing (i.e., corroboration) of Given that a well-tested general understand- many phylogenetic hypotheses without indepen- ing of phylogeny (its estimation at best) is a nearly dent transformational and functional understand- universal goal among modern systematists, the ing. The currently dominant view eschews the first reaction that comes to mind regarding the relevance of adaptational analysis for phylogenet- adaptedness of past samples of lineages (the fos- ics, if not for so called “scenario building”, as I sils) among theoreticians (often neontologists) is briefly discuss later. According to this view, cla- that they are dead, so what, if anything, can be dograms, based on parsimony-driven distribution said about their adaptations with any degree of cor- analyses of ”synapomorphies” (i.e., untested roboration? It should not need repeating here that homology hypotheses of uniquely shared similari- science is a probabilistic enterprise with equal ties between taxa), represent the foundations doses of deductive and inductive activities, contra (deductive and scientific) of all other historically rel- the Popperian views endlessly defended in the evant analysis (e.g., Eldredge and Cracraft 1980; pages of Cladistics, and that its various problems Simmons 1993; Novacek 1996). can be ”solved” or even “resolved” only with varying degrees of success (e.g., see, again, the Pop- FUNCTIONAL BIOLOGY AND TERMINOLOGY perian and logical-positivist text on cladistics by A few concepts should be discussed at the Schuh 2000,). Yet some of the least “falsifiable” or outset before attempting linkage of functional biol- “provable,” but often well-corroborated, answers to ogy with phylogenetics. This is in order to explain questions can be the most important for under- and differentiate among issues that have not been standing causes and history (these often being the uniformly understood, advocated, or espoused by least logical in a linear sense). workers in any of the methodological areas related Adaptations in fossil taxa cannot ever be fully to functional analysis. To most naturalists func- understood, but it is also questionable, to a lesser tional biology has a unifying significance for evolu- degree, whether they can be completely under- tionary biology. This holistic, and Darwinian, stood for most living species as well. The reason perspective of naturalists should axiomatically for the latter is partly theoretical, but primarily apply in the pursuit of phylogenetics; organisms because the operational difficulties can be enor- have always represented specific strategies to dif- mous for complex metazoans. These issues are ferentially survive and reproduce, so this fact independent of the adaptive nature of the evolu- should have a bearing on any estimation of phylog- tionary process itself. We need to remind ourselves eny.4 A broadly conceived notion of functional biol- at this point that we should be equally aware of the ogy is certainly not evolutionary biology in toto, but fact that, although phylogeny also resides in the it is at the core of biological as well as macroevolu- past, we nevertheless pursue it with zest. And tionary explanations for the history of life. But there there are very good reasons why we should, there- are issues related to the term “function” that need fore, do the same with regard to functional and to be examined because these relate not only to adaptive analysis for both fossils and living spe- the clarification of the term but also to phylogeny cies. There is surely more to adaptational analysis reconstruction itself. of fossil entities than Novacek’s (1996, p. 315) remark that “[t]his situation leaves us looking for Bock and von Wahlert on Function something to salvage for the purpose of scientific In an attempt to unravel and clarify the several inquiry.” Does this mean that often the litanies of meanings of the term function, a more restrictive dubious synapomorphies that overwhelm many use was suggested by Bock and von Wahlert morphological databases in cladistic analyses of (1965) in a paper on adaptation and the form-func- fossils are the proper foundations for a cladogeny tion complex. These authors refined the distinction that should guide adaptational assessment? between the mechanical-physiological and behav- Ontological issues surrounding adaptation as ioral aspects of features of organisms, on the one a process, because of the thorny issue of “current hand, and the selection-caused (-mediated) biolog- utility”, cannot be resolved (see later). Such philo- ical role (biorole or role; or adaptive or biological sophical conundrums, however, do not make the function) of these, on the other. Such a conceptual process of adaptation and its results any less real. difference was previously well understood by a But it should be realized, because it is not widely number of biologists and paleontologists, but it was appreciated, that the explanation of adaptations in

4 F. S. Szalay: Function and Adaptation in Paleontology not appreciated by many others. The concepts of ently structured mechanical systems (e.g., his mechanical and biological functions (i.e., function examples of forearm mechanics), although per- and biorole) were not only clearly differentiated by forming the ”same” roles, surely have a distinct Bock and von Wahlert but were presented in a the- combination of mechanical factors and resolution oretically detailed functional and ecological con- of forces acting differently in concert. Such sys- text. This clarification of terms to cover tems certainly do differ in their mechanics. Model-T definitionally well-differentiated (but really only Ford and late-model BMW automobiles all roll empirically divisible) research domains remains along the same road from point A to B, but no one important. But the theoretical relationships would seriously entertain the notion that their between mechanics and adaptation are more com- detailed (progression-related) mechanics are complex than normal definitional procedures permit parable. (see later). This issue of function is further confounded by I and others have followed the terminology Lauder (1996, p. 63) when he notes that “[t]he bio- introduced by Bock and von Wahlert (1965) logical context of structure and function is referred because such practice has the salutary conse- to as the ‘biological role’ of a structure or mechani- quence of forcing both an author and his or her cal function…” (emphasis added). In spite of what reader to think more clearly about the complexity of I believe to be Lauder’s misuse of the conceptual functional, adaptational, and evolutionary issues. and terminological meanings of function, these dis- In any meaningful sense, the mechanical and bio- tinctions continue to serve a significant purpose in logical functions of organisms in realtime are comparative biology. When viewed theoretically, inseparable (see Szalay, 1999a for discussion of both the mechanical and biological functions can “realtime”). Yet a combination of historical and real- change (e.g., from bones to neuronal networks). time factors - ontologically but not epistemically Both can change independently of one another and distinct - clearly drive evolutionary changes of func- have independent historical components. It is tioning attributes.5 These are wholly interdepen- important, therefore, not to front-load the historical dent processes and causalities. Note again, component (the structural-functional heritage) with however, that many researchers continue to use fitness considerations within the already enor- the single term “function” with a clear meaning mously complicated theoretical maze regarding where the context renders it obvious that they function. By not keeping the biological role inde- mean either mechanical or biological (adaptive) pendent of mechanical explanation, Lauder has function. Others, however, continue to conflate the done just that. meanings at the expense of both operational and The “new adaptationism” that has become explanatory clarity. wedded to a taxic conceptualization of parsimony- Lauder (1996), in spite of his attempted based cladistics and has been hailed by many endorsement of the functional conceptualization of (e.g., Novacek 1996) as the solution to the problem Bock and von Wahlert (1965) either intentionally or of functional conceptualization has not advanced inadvertently confused this approach with ”ahisto- the cause of either terminological or theoretical ricity” versus ”historicity.” When Lauder (1996, p. clarity. The ”causal role function” notion in this “new 63) states that “… a bone might have the mechani- adaptationism” is an unnecessary and invalid sub- cal function of stiffening the limb against gravity …” ordination of the adaptational component of phy- he is not only referring to mechanical function. In logeny to a theoretically truncated (= ontologically making such a statement that connects an organ- unrealistic) epistemic paradigm of numerical cla- ism (and, needless to say, the size of the animal, distics. This view of the cladistic component of phy- and the manner of its locomotor and other posi- logeny has come to mean not only that taxograms tional behaviors) to its specific environmental con- are phylogeny, but that evolutionary explanations text, Lauder clearly adds an adaptational, and (and even theory) should be based on such taxic therefore selectional force-related, component to constructs. his characterization, which he refers to as “anatom- Taxic and Punctuationist Perspectives by ical function.” He obviously believes that there is a Gould and Vrba on Adaptation and Function difference among the relationships of an anatomi- cal structure, its biological role(s), and what he pur- Gould and Vrba (1982) offered a terminologi- sues as the neurologically controlled behaviors of cal scheme through which they asserted that one an organism. In making this distinction, he either can clarify differences between adaptations due to rejects or misses the universality of meaning natural selection for their current role, and various attached to the function and biorole dichotomy so aspects of such features that were not built by well explicated by Bock and von Wahlert. Differ- selection for their current role, but became useful

5 F. S. Szalay: Function and Adaptation in Paleontology for it after their inception. These authors argued realized functions (including their phenotypic that this was partly an effort to replace ”preadapta- expressions as adaptations). Simpson envisaged tion”, a concept they considered teleological. the adaptive process as an ongoing seamless rela- According to Gould and Vrba (1982), “aptation” tionship between the total environment and the was the general phenomenon of something being evolutionary unit at a given moment in the history fitted for a role, whereas the term “adaptation” was of that lineage. Gould and Vrba (1982), on the restricted for traits built by selection for current other hand, based their discussion on the underly- roles and the term “exaptation” was used for the ing assumption (never made explicit) of the myste- concept of preadaptation.6 rious and abrupt shifts of speciation. Their The example they used, feathers (without a conceptualization, and the resultant and ungainly much-needed clarification of the kind of feathers), terminology loaded with unacceptable theory, is has a considerable semantic element to it. The based on the coded core of punctuationism, pale- term “feather” covers various kinds of feathers, the ontological species taxa that happen to coincide expected state of affairs for all evolutionary trans- with the terminal species taxa of cladistics. formations of attributes through phylogeny, each The mental imagery offered by the punctua- representing part of a continuous, but at any histor- tionist and taxic terminology is clear: Species give ical moment possibly distinct, condition of that trait rise to other species with sharply distinctive adap- or group of traits. Although feathers are a general tations, a perspective that studiedly underplays the developmentally circumscribed group of features, it rate-independent gradualism of phyletic continuity is obvious that whatever kind of feather came first and exhorts terminology related to species taxa in a particular lineage (probably the protofeather that serves a speciational theory of evolutionary for improved thermoregulation, from a preexisting change.7 condition that we would call a type of scale) was Causality and Function not the same kind of feather that was subsequently developed through selection for flight, or the daz- An issue of seemingly remote relevance to the zling variety of display feathers developed through theoretical notions embedded in ”function” is the sexual selection in birds. As noted, we could also dichotomy of ”proximate” versus ”ultimate” desig- have begun by calling feathers a particular type of nation of causes in biological explanations. Mayr’s denticulate scale along a continuum of scales (and (1961) early, popular, and much repeated thesis of bushy phylogenetic patterns), a sequence that (Mayr 1982) was that there are both proximate and undoubtedly was part of the transformation series ultimate causes operating in biology. The former of scales in general. The same applies for verte- (the mechanics, physiology, etc., of an organism) brate limbs, from fins to wings of all sorts. This was pursued by the ”functionalists,” and the latter highly semantic, as well as “lurching” and “jerky,” (the adaptations and history of species) by the conceptualization, just one of the many possible, ”naturalist-evolutionists.” Mayr believed that played a major role in Gould and Vrba’s theoretical sharply different conceptual approaches were presentation. needed to understand these causes. I take a con- But the proposed sharp division between trary position. The concept of causality in realtime “exaptations” and adaptations does reflect two (Szalay 1999a) should play a fundamental role in important underlying messages, and the agenda is any theoretically rigorous connection among the clearly punctuationist. First, and this view is not various components of both ”nonhistorical” and particularly controversial, lots of features just hap- ”historical” causation and explanations in holistic pen; they are non-adaptive. The second point, functional biology. (Note that the latter is consid- however is that the advocated (punctuationist and ered biosystemism by Mahner and Bunge 1997, taxic) view of evolutionary change should have a who maintain the special position of organisms in distinct ”aptive” component assigned to (punctu- the various levels of organismic and suborganismic ated) species taxa (either the first or the second diversity.) Therefore a loose designation of cause kind of ”aptation”). Furthermore, and subsequently, can be obfuscating when it comes to either func- a lineage perspective on evolution - the Darwinian tional or evolutionary analysis, both in the broad view - should be abandoned in favor of a “stable- and narrower senses (see later). Causes occur in taxon”-based notion of punctuationism. realtime (and that rules out ”causal” past history), This was a very different conceptualization although obviously the initial and boundary condi- from Simpson’s (1953, p. 160-199) expansion on tions of organisms living at a particular time play a Darwin, namely that the prospective functions in a significant constraining and facilitating role dynamic overlap of the shifting relationship throughout their entire life. The initial and boundary between a lineage and the environment become conditions together are a rough, if not exact, equiv-

6 F. S. Szalay: Function and Adaptation in Paleontology alent of Aristotle’s material cause from his “techne” Ontological Perspectives on model of causation. I adopt the view of Mahner and Functional Biology and the Omission of Bunge (1997) on causality, except for their insis- “What Something Is For” 8 tence that ontogeny is not causal. The arguments I am not critical of the epistemologically signif- of Mahner and Bunge challenge the notion of ”ulti- icant distinction found in practical research pro- mate causality” outside of the context of realtime grams that pursue sundry important functional causality in any lineage. aims in the laboratory without immediate concern It is important to frame both questions and for field-related bioroles. But we are repeatedly research strategy not in terms of almost invariably reminded of the fact that the concept of function is nebulous “ultimate causes” lost in the past, but understood very differently by many who consider rather in terms of the knowable but obviously con- themselves to be structuralists, functionalists, phy- strained material realities of the organism we logenists, or adaptationists; a somewhat unfortu- 9 study, be it fossil or extant. It is obvious that any nate, although often understandable, compart- manifestation of the organism throughout its entire mentalization of what should be a theoretically life history is deeply functional in the broad sense, cohesive whole. and any such functions are as historical as they are In addition to the varied meanings of function, adaptive. Furthermore, a phylogeny is tested for example in the community of students who against these, in contradistinction to the “new study musculoskeletal morphology, there are a adaptationism” paradigm that would map features variety of technical approaches that require novel discovered in these contexts onto a taxogram. conceptualizations. New approaches addressing Organisms themselves reflect both history and questions on sundry levels and that apply equally adaptations in an inexorably intertwined manner to skeletons, bones, trabecular structure, and bone that should be analyzed to factor out the historically tissue types have been, and are being, developed. shared (or sequentially related) components of Such epistemological avenues rest on different phylogenetics. assumptions from level to level, as researchers Historical narratives are histories of success- consider bone tissues, bones, and skeletons from ful and successive ontogenies wastefully managed different perspectives. Nevertheless, beyond the by ecology,10 and lineages represent ontologically basic epistemological issue (namely that there are the past history of evolving populations or species clear conceptual differences between mechanical (anywhere along that lineage in time). Therefore, a functions and biological roles), there has been an lineage (a mere record of a species) does not have increasing conceptual redefinition and narrowing, ”causes” acting on it, beyond those that acted on as well as confusion, concerning the theoretical the aggregate of living individuals that made up meaning of functional studies. Theoretical posi- each segment in the past (a species, or other evo- tions have been taken by authors proposing vari- lutionary subunits of a species, in an instant in ous exclusive meanings for the concept of function. time; such realtime units are not species taxa; see Whereas some of these positions are largely epis- discussions in Bock 1979; Szalay 1999a). Real temological in nature, some have taken on the causes that affect, for example, the becoming of a cloak of ontological propositions in claiming some single organism are demonstrated by the newly special theoretical virtue for them. emerging ”hybrid” fields (e.g., developmental For example, in a long series of papers going genetics dealing with issues of evolutionary homol- back two decades, Lauder (see Lauder 1981; ogy, often called ”EvoDevo”). These disciplines Amundson and Lauder 1994; Lauder 1996; and show with increasing precision how inseparable references therein) advocated a rather narrow view functional explanations are, not only from history of functional morphology that sought connections but also from adaptive existence. Mutations and between the parsimony-based taxograms of ”pure” their developmental consequences are inseparable systematists and a quasi-engineering type of func- from the context of a particular genotype. This is tional analyses. These efforts either implicitly or well beyond the occasionally agenda-laden and explicitly eschewed connections to adaptation, and quasi-engineering concepts of function that they were devoid of any input from a selectional (= eschew adaptations and adaptedness, such as the Darwinian) perspective. In fact, in Amundson and kind of functional conceptualization advocated by Lauder (1994) the claim was made that adapta- Cummins (1975), Amundson and Lauder (1994), tions are all but impossible to identify and therefore and others. the search for the “why” of attributes (namely what selectional causes molded a feature) is doomed to failure. The justification for this narrow view of func-

7 F. S. Szalay: Function and Adaptation in Paleontology tionalism (actually a form of structuralism, see contextualize polarity determination, as well as the later) is that they believed that the mechanical stratigraphical and biogeographical contexts, all at transformation of structures is what functional biol- a level that information and the applications of valid ogy is about, without regard for the specific time- methods permit. This is an attempt to understand contextual roles of natural and sexual selection. the phyletics of features. These strictures apply Yet this theoretically restricted perspective did not proportionately to the degree that any of these prevent Amundson and Lauder (1994) from calling activities can be brought to bear on a research their conceptualization, inexplicably, “causal role project. This, in turn, obviously depends on the function.”11 nature of available evidence (including both deduc- This “causal role function” perspective (with its tive and inferential information). But the various thinly disguised disdain and its rejection of the “less levels of inference permitted by data and context rigorous” research under “old adaptationism” do not alter the validity of a conceptual methodol- aimed at uncovering adaptive functions; see Rose ogy derived both from descent and from natural and Lauder 1996) is a direct outgrowth of the “cla- and sexual selection in a specific space and time. dogram first” research program (e.g., Eldredge and To claim theoretical primacy for a phylogeny based Cracraft 1980; Lauder 1981). This strictly conform- on statistical sorting of structural patterns, com- ist and fundamentally Kuhnian research program bined with only a sensu stricto functional analysis subjugates biological character analysis to taxic which would transfer functional evolution into a schemes of bifurcations and foregoes the neces- non-Darwinian vacuum is not based on sound the- sary prerequisite of testing character transforma- ory. It is a flawed conceptual method for attaining tions with the aid of methods derived from tested an understanding of ”functional evolution” as its evolutionary theory (i.e., the phyletics of features). professed goal. The concluding remarks of Leroi et But any evolutionary scheme or theory is wanting al. (1994, p. 398) regarding phylogenetics are sig- and distorted without adaptation as part of the evo- nificant in this context. “Such analyses will be all lutionary process.12 Ironically, such a pattern of the more robust for lacking unsupported assump- cladogeny is just as unknowable in terms of cer- tions, unwarranted inferences, and untestable tainty (particularly without phyletics, and not only hypotheses about the history of evolutionary mech- because the concept of scientific corroboration of anisms.” It can be added that these linear analyses an ancestral stage is excluded from cladistic the- of nonlinear relationships are also not only sterile, ory) as is the adaptive function jettisoned by but theoretically vacuous. Lauder and colleagues. In fact, there are grada- The theoretical stance of Amundson and tional or incremental probabilities in the testing pro- Lauder (1994), in which they attempted to exile cedure (corroboration, verification, or rejection), Darwinism from functional biology, is in essence a often with a considerable overlap between both narrow functionalist (structuralist) exegesis of the phylogenetic and adaptational hypotheses. It is early wave of zealotry of Anglophone cladistics that such overlaps in the analysis that allow for the dis- declared its total independence from evolutionary tinction between homologous and homoplasious biology and claimed primacy for nested cla- similarities. dograms of taxa, taxograms, before all else. The On theoretical grounds that seriously consid- additional claim for primacy for a pure mechanics- ers the role of developmental biology (particularly based view of function in biology also reflects a modularity) in the evolutionary process and the view that regards deduction from physical laws as irrelevance of parsimony-based decision making superior to the inductive procedures necessary for for character transformation, I do not believe that historical explanations. Because a strong inductive an engineering analysis of taxa based on their component is required in all adaptational and his- position on taxograms is a meaningful approach to torical assessments of patterns (see Bock, 1981; phylogeny estimation. This approach, which Szalay and Bock 1991), the connections of func- depends on a misplaced fealty to someone else’s tional-adaptive analysis (including transforma- cladogram (and to the parsimony paradigm) to tional analysis) to phylogenetics (see Figure 1) is explain evolutionary transformations, is flawed at usually unacceptable for doctrinaire cladists and its foundations by its circularity. Yet obviously func- “new adaptationists.” Although parsimony-based tional, phyletic, and cladistic evaluations of distribu- cladistics strives to recover history, it also aims for tional data must be an integral part of reliable a completely deductive, Popperian methodology phylogeny estimation. Both the establishment and (openly admitted only by pattern cladism; see the explanation of meaningful patterns (not just the especially Schuh 2000). structural and mechanical manifestations of shape) The combined perspectives of parsimony- require some adaptationally-framed assessment to based cladistics and “causal role function” proto-

8 F. S. Szalay: Function and Adaptation in Paleontology

Figure 1. An interim schema for Darwinian phylogenetics. The directional arrows indicate the causal interdependency of the first three domains for both generating data and testing hypotheses. Note that, although the interrelationships for the first three domains are really ”temporally looped,” they are not circularly dependent on Domain 4, which is to be derived from them. The direction of arrows indicate the domains, databases, and tested hypotheses within these domains against which other hypotheses are tested. cols that consider adaptational understanding unat- evolutionary analysis means a contextually vari- tainable are being made obsolete by many able dependence on adaptation-related consider- multidisciplinary efforts created from the fusion of ations. These are manifested (e.g., in vertebrate genetic, morphological, developmental, ecological, paleontology) mostly as structural patterns of and paleontological perspectives and practices, to aspects of skeletal remains. mention only a few.13 The deduced engineering I include here a relevant, albeit rhetorical, patterns in a ”causal role function” approach, of query. What does the comparative assessment of course, can be superimposed onto, if not meaning- engineering parameters mean without any concep- fully interdigitated with, parsimony-based cla- tual room left for the reasons for these differences? dograms. Such practice of circularity is essentially Whenever civil or aeronautical engineers plan the similar to attempts at a “transformational analysis” construction or analysis of structures, there is that hope to procure evolutionary transformations always a particular goal in mind. That goal is, prop- from taxograms.14 erly, the Aristotelian final cause, namely “what So, in contradistinction to the paradigm of something is for.” This implicit factor is absolutely “causal role function” advocated by Amundson and and fundamentally connected to any mechanically Lauder (1994), such restrictive functional oriented enterprise, and if such an effort is sepa- approaches lack a valid framework for evaluation rated from its context it loses not only its directives without the ecological (adaptational) component, and limits but also its meaning. Unlike the ”causal as vague as adaptive meaning may be in some role function” protocols, Bock (1999), who also instances. The pivotal role of contingency-based maintains a sharp divide between function and

9 F. S. Szalay: Function and Adaptation in Paleontology adaptation epistemologically, makes the obvious tions of the latter should depend on the former.16 connection between these efforts. In Bock’s view, Bock’s theoretical perspective appears to be tied to functional and adaptational or utilitarian analysis Mayr’s (1961) claim regarding distinct proximal come under the same conceptual and theoretical (which Bock called functional) and ultimate (which heading; both are functional explanations. Bock called evolutionary) causes (which Bock It is hard to contemplate how a particular well- more meaningfully called explanations). Bock substantiated biorole (or one inferred with a lesser (1999) maintained that functional morphology degree of probability than samples of direct obser- answers “how” questions, namely how things work. vations provide), correlated with form-function, I, and others, obviously do not disagree. But the would not have played a major causal evolutionary questions and problems of functional biology role in the becoming of that complex, except in a (sensu lato, the sense endorsed here for the theo- strongly structuralist conceptualization of biodiver- retically most inclusive concept) arise from a much sity. An increasingly narrow emphasis on engineer- broader context than just structural statics and ing function can result in a peculiar evolutionary mechanics, or chemistry. Bock’s own view on evo- conceptualization, not to mention the problem of lutionary explanations that these are responses to discordant semantics. Is such conceptualization questions of “… why attributes of organisms came really good theory? The fundamental insight of into being originally and have modified (= evolved) Lamarck, reworked within Darwinian theory, that over historical time” (1999, p. 49), indicates, how- the combined function and role of attributes is part ever, that a certain critical theoretical perspective is of the causal interaction responsible for their evolu- missing. tion has been pursued by many biologists and phi- This quasi-artificial ”functional” versus ”evolu- losophers; its theoretical consequences are not tionary” theoretical dichotomy highlights a lack of discussed here.15 In a definitional sense, at any formal recognition that in any evolutionary change moment in lineage history a form-function complex the usual “why” question alone is not an adequate that exists is a set of initial conditions and the sun- formulation of the nature of evolutionary explana- dry causes that act on the organisms are, strictly tions. Evolutionary functional explanations (sensu speaking, the causes that mediate subsequent lato) have an ineluctable transformational compo- evolution (survival and resulting fitness differ- nent that render mechanical or role-related notions ences). But it cannot be overlooked that the very of function incomplete and therefore theoretically phenotype-based activities of organisms generate inadequate. In fact, any full evolutionary explana- a great deal of the specific causal forces acting on tion that deals with specific lineages of organisms them, as has been repeatedly pointed out. The has, as its integral component, the issue that how feedback loop is mutually dependent, and the something works, in light of what it is for. And understanding of the process fully justifies an therefore it is critically dependent on how a particu- expansion of the conceptual methodologies based lar trait prevalent in a lineage came to be histori- on it. Epistemological advances follow such a theo- cally transformed and ontogenetically constructed retical stance. that way. At first this may appear to be insignificant. But what about the specific research protocols But on second thought, it should be realized that that should rest on conceptual foundations different contingent lineage-specific changes are not from those of engineers if the goal is an evolution- “merely what happened” (contra Bock 1999, p. 56). ary understanding? Strictly functional explanations, Such changes, the selectional guidance notwith- although they may justify deductive issues dealing standing, were profoundly influenced or guided by with features, are incomplete for species-specific preexisting stages (as they will have influenced phenotypic attributes. To recast and paraphrase subsequent changes). There is virtually universal Dobzhansky, they lack explanations for their spe- agreement that these contexts (the heritage) guide cies-specific, hence idiosyncratic, workings. The both the nature of transformations as well as their perspective criticized here, repeated for decades adaptive ”goodness,” ”latitude,” and even built-in both by doctrinaire cladists, as well as by the pure seeds of doom (in retrospect) or new opportunities ”functionalists” such as Lauder and colleagues, is of given lineages in given environmental or com- quite different from Bock’s frequently taken stance petitive contexts they will encounter.17 Realtime (e.g., Bock 1988) that functional (sensu stricto) and constraints (rooted in history) do not only constrain, ecological components of, for example, morphol- but they direct and facilitate subsequent modifica- ogy, are independent and complimentary. Never- tions. theless, Bock does profess a belief that a sharp Such conceptualization should have profound theoretical dichotomy regarding function and adap- implications for methodologies that aim to decipher tations is the proper view and that the investiga- evolutionary history. For example, the literature on

10 F. S. Szalay: Function and Adaptation in Paleontology the history of understanding the origin, transforma- 1977, 1981) applied what I believe to be a some- tion, and function of tribosphenic teeth of therian what restrictive, more logic- than probability-based mammals and the resultant evolutionary patterns perspective when it comes to extinct organisms. constrained by the genetic and occlusal dynamics Given good and complete specimens, specific of the original molar system supply some of the adaptive strategies can be understood in fossil most numerous and persuasive examples of the taxa with high confidence, because the judicious meaning of constraint. Both the historical and the and phyletically contextual use of combined functional (occlusal and ecological) constraints mechanical, adaptational, and ecological models of profoundly affected morphology, function, and bio- living organisms can render great certainty to this logical roles throughout phylogeny. Examples type of paleobiological analysis. This type of mod- abound in virtually all systems of vertebrates, the eling through the use of carefully delineated skeleton being no exception. aspects of living species can yield an important Bock’s (1988, p. 207) view that adaptational understanding for both adaptational and phyloge- explanations are not evolutionary but functional, netic analysis (Szalay and Sargis, in press). therefore, is also problematic, particularly because It bears repeating here that very often we can Bock (1999) continues to maintain the legitimacy of corroborate far better the adaptive strategies of the theoretical independence of functional (proxi- well-known fossil species than their phylogenetic mate) and evolutionary (ultimate) explanations. affinities. I suggest, therefore, that perhaps the Explanations of adaptations are in fact inseparably construction of completely deductive, syllogism- both; they are ”temporally looped” rather than hier- like, ontological statements that are deduced from archically and dependently related to form-func- the logical consequences of otherwise clear empir- tion. While natural and sexual selection are law-like ical research-based definitional differences (such explanations, their consequences in lineages are as the distinction between function and biorole) is also fundamentally historical and time-dependent not the most useful approach to theorizing in this processes that are never disembodied from the area of evolutionary analysis. Such assertions particular lineage histories (e.g., Szalay and Cos- carry well-corroborated definitional concepts to tello 1991). As Bock (1993) so aptly emphasized, their logical extreme, but not necessarily to new, natural selection is cause, mechanism, and pro- theoretical heights. Both the deductive and the cess, depending on our use of and the context of purely epistemological limitations, as in the case of the concept. The acquisition of new adaptations or strict functionalist theory, are unjustified. a new form of adaptedness (both are processes) is Let me also reiterate the obvious. First, the a large component of evolutionary history, and level at which adaptations and adaptedness may much of phenotypic evolution, as most evolution- be ascertained in organisms is unequivocally the ists suspect (and long championed by Bock), is highest for living species observed in nature. But fully Darwinian; it is causally propelled at the lest we forget, it is equally obvious that existing organism level (see also the organism-centered features in an organism may reflect causal correla- biosystemist approach of Mahner and Bunge tions between these form-function complexes and 1997). the use they had in the past. In fact, the very logic Ecomorphology (or any aspect of the pheno- of descent with adaptive modification demands type related to bioroles) is conceptually very much that, given the temporal nature of the evolutionary a part of this endeavor to understand attributes process, it be understood clearly that the current because this field forms the context with its insepa- attributes of organisms are the products of selec- rable feedbacks into the strictly functional efforts in tional forces acting on past generations. Activities laboratories. The deductive base of these efforts at a given time (in the particular context of the does not make them superior or axiomatically ante- existing environment) generate the selectional cedent to ecomorphology. Although Bock (1999) forces that either maintain or transform the fre- argued for the distinction of ecological morphology quencies of fit individuals with the appropriate phe- from functional morphology and the notion that the notypic attributes. But this frequency-changing (or - former is built on the latter, he nevertheless fully maintaining) response regarding the adaptations is endorses the importance of adaptational analysis. in the succeeding populations. This temporal rela- This is in contrast to Lauder and colleagues (see tionship is critically important. Lauder 1990, 1996; Leroi et al., 1994), whose The only (probability-based) factor that is expressed futility regarding adaptations is more in likely to assure successful programs in adapta- service of “causal role function” than any theoreti- tional studies (those with high truth content) is cally and empirically tenable position in Darwinian based on the realistic assumption that the rate of theory. In spite of his stance, however, Bock (e.g., environmental change is usually slow in relation to

11 F. S. Szalay: Function and Adaptation in Paleontology generation time (certainly gradual or static, short of ecological morphology that is applicable to living extraterrestrial impacts or violent local distur- species only is unfortunate. It appears to be a bances), or often approaches zero (in generational monotonic logic-bound consequence that unneces- terms), resulting in stabilizing selection, often with sarily truncates adaptational analysis, which is a fully Darwinian progressive change for the same always probability-based. It also unjustifiably nar- biological functions. What organisms do, therefore, rows the valid epistemological limits of the testing in their currently observed environment is probably of a tremendous range of issues in macroevolution. causally connected to their features. I emphasize again that adaptational assessment of In addition to the foregoing general theoretical well-known fossils is not any less dependent on point regarding the absolutist perspective on the probability judgements than is phylogeny estima- study of adaptations in our own time, there are sev- tion in general. eral other issues that have surfaced in regards to an exegesis of the logic of ”current utility.” The FUNCTION, ADAPTATION, AND statement by Bock (1999, p. 55; and personal dis- PHYLOGENETIC ANALYSIS cussions regarding adaptational analysis in fossils) In examining the problem of conflicting views that the “[s]tudy of biological roles must be done by about mechanical and adaptive functions and phy- observations of the organism living naturally in its logenetics, I will not argue that some degree of environment—they cannot be determined by functional knowledge in the broad sense is impor- observations made in the laboratory or other artifi- tant for any causally meaningful understanding of cial conditions” is a case in point. No one would character ordering and polarity to estimate evolu- argue that for highly specific activities contained in tionary history. To me this is obvious. Taxograms the form-function features of living organisms infor- based on parsimony analysis, as Mahner and mation from the natural setting is critical. But we Bunge (1997) called them, are only ”pretheoretical can counter that a host of highly relevant explana- classifications”, with their studied emphasis on pre- tions about fossil taxa, using rigorously constructed theoretical, not phylogenies. But in reading the lit- models already alluded to, are equally justified, erature related to functional analysis and its often approaching a high degree of probability at connection to phylogeny, it is also obvious, as given levels comparable to those made about living alluded to previously, that even students who are organisms. In fossil mammals, based on this type deeply convinced that functional explanations must of rigorous and relevant modeling, there are role- be somehow part of phylogenetic explanations related attributes at these levels such as cursorial have conflicting views on the very concepts of modifications, aquatic adaptations, digging adapta- function: what is and what is not “scientific” in functions, habitual hanging, obligate arboreality or ter- tional biology, and how functional studies bear on restriality, and hosts of obligate dietary adaptations phylogenetic explanations. such as grazing, myrmecophagy, piscivory, and There are usually obvious levels of resolution, hypercarnivory, all on a level of generality that can both for adaptational and phylogenetic assess- be securely ascertained (Court 994; Szalay 1994; ments, and these will vary according to the nature Szalay and Lucas 1996; Szalay and Schrenk1998; of available evidence. As I see it, there are, mini- Szalay and Sargis, in press; and references mally, two important and related questions regard- therein). A particularly excellent example is Court’s ing the significance of adaptational analysis and its (1994) analysis of limb posture and gait in the prim- relationship to phylogenetics: How reliable and itive Eocene fossil proboscidean Numidotherium. independent are functional, adaptational, and phy- Such modeling employs ecologically and function- logenetic estimations, and can they be truly inde- ally well-understood living species that cross size pendent?; and how is phylogenetic analysis and higher taxon limits, thus providing a degree of connected theoretically, and therefore methodolog- adaptational assessment through the conver- ically, to functional biology (sensu lato)? gence method, which is not only highly reliable but It is my position that the feedbacks in a rigor- which forms a critical link to other activities such as ously comparative framework between form, func- phylogenetic estimations (e.g., Szalay 1981; Sza- tion, adaptive appraisal, and phyletics of features lay and Sargis, in press). As in any other methodol- (the temporally looped relationship noted previ- ogy axiomatically derived from underlying tested ously) and the full consideration of the fossil record theory, none of this is logically full proof but rather make for robust hypothesis testing. Employing is probability-based. holistic Darwinian explanations for character com- Therefore, to consider the assessment of plexes is far more scientific, in a biological sense, causal factors for the features that derive from the than any Popperian, deep-time-deprived, and obligate activities of organisms to be a method in

12 F. S. Szalay: Function and Adaptation in Paleontology structuralist pursuit of morphology by itself can disparate form-function strategies in achieving that be.18 With this combinatorial analysis of extant and way of life, that the various clustered ”synapomor- fossil data and with a full immersion in the most phies” derived from parsimony analysis (most of current understanding of developmental biology these being previously poorly assessed adaptive or (including developmental genetics), if the level of merely verbal “similarities”) of the living species of analysis demands or permits, homologies can be the American and Old World groups were not distinguished from homoplasies with confidence. homologous by either structural or functional-adap- We may ask now, in what specific way is func- tive criteria. Consequently, they are not indicative tional analysis conducive to phylogenetic estima- of ties between the palaeanodonts and Eurota- tion? I would first like to reject the theoretical mandua, on one hand, and pangolins, on the position inherent in often-cited cover statements to other. The inferred adaptational background for the the effect that an investigator “will consider function fossils and their structural-functional assessment in whenever it is useful beyond ‘character’ analysis” that light were fundamental in reaching these taxic or “functional information is merely more grist for conclusions. Homoplasies could be rejected prior the mill” in the construction of ephemeral data- to taxic analysis. Subsequently, corroborated phy- bases for parsimony analyses heading for “consen- logenetic trees fall out of such a character analy- sus,” as both of these positions are sometimes sis.21 The Darwinian method is certainly not the stated and implied (e.g., Simmons 1993; I will not straw man characterized by claims of cladists expand the discussion here on the obvious that a regarding functional-adaptive analysis (e.g., science of evolutionary history that aims to dis- Schuh, 2000) that “only adaptive characters are tance itself from a causally meaningful testing of used in phylogenetics” by Darwinians. In fact, it is phylogenetic hypotheses is a greatly diminished the incidental and phyletically informed attributes in one). addition to the adaptive solutions that are sought to Quite simply, as originally outlined by Bock add to a data base as either shared and derived or (1981), functional-adaptive analysis is character transformationally revealing attributes. analysis aiming to establish the reliable homolo- The alternatives to a Darwinian analysis of gies, be they synapomorphies or transformational morphological attributes particularly the cranioskel- homologies with highly corroborated directions and etal characters that vertebrate paleontologists rely sequences, as distinct from homoplasies.19 This is on and that I am most familiar with, usually offer a fundamentally a Darwinian approach to phyloge- method through which a mixed suite of similarities netics, because it is a selection-related evaluation are subjected to parsimony procedures to sort out of features in an evolutionary context. In fact, the homoplasious and homologous similarities. The foundations of this view were clearly enunciated by evolutionary vacuum (i.e., a lack of theoretical justi- Darwin.20 Given the geological and geographical fication) within which, I believe, this method is prac- contexts and an understanding of developmental ticed has been discussed elsewhere (Bock 1981; homologies, functional-adaptive analysis of fossils Szalay 1994). But beyond the general weakness is and living forms (the latter the designated models the complete elimination of the explicit research- that are researched in detail; Szalay and Sargis, in based phyletics of the characters used. Phyletics, press) can inform with often great confidence which includes both the ordering and polarization about homologous versus homoplasious features of characters, is conflated with taxic analysis, as in the comparison of details of functioning com- often there is nothing beyond taxic sister-group plexes that perform an adaptive function. arrangements that might give justifiable indications As one example, in a recent study Szalay and of a direction of transformations of non-identical Schrenk (1998) compared the living ”edentate” and (hence, not truly synapomorphous) traits. Strato- digging mammals (the xenarthran Cingulata and cladistics also endorses a parsimony-driven cladis- Myrmecophagidae, and the Pholidota), with fossil tic approach but adds a stratigraphical dimension ”edentates” such as palaeanodonts and the Messel that improves the reliability of its taxograms (see Eocene Eurotamandua. The numerous function- Fisher 1994). It invariably appears that parsimony- driven polarity determinations of this study of the based cladistics happens without attempts to inde- enigmatic phylogenetic relationships involved a pendently test postulated synapomorphies. high-probability adaptive framework, specifically The whole enterprise of phylogenetic estima- that the fossils were also myrmecophagous and tion or analysis is a highly probabilistic one. If this had obvious digging adaptations, either to get at is accepted—and I believe that it should be—there food or shelter. Going beyond the well-established can be no theoretical objections to a procedure similarities relating to the myrmecophagous and that is based on the guidelines provided by the digging habitus, it was concluded, based on the mechanical and adaptational analysis of living and

13 F. S. Szalay: Function and Adaptation in Paleontology fossil species and their specific aspects. Most Transformational analysis, whether based important, adaptational assessment sets a frame- solely or partly on the sequences offered by the work for a character analysis that is also necessar- fossil record, and morphological analysis based on ily transformational, as we need to decide rationally functional-adaptive foundations are the corner- (based on sound theory) the ancestral and derived stones of phylogenetic analysis. Any and all theo- conditions. Such character analysis permits the retically meaningful contextual determinations of rejection of homoplasies and allows for ancestor- which trait is primitive and which is advanced descendant or branching level-specific corrobora- involves some type of transformational assess- tion of homologies for taxic analysis, based on ment and should use a geographical and strati- some biologically and paleontologically meaning- graphical perspective when these are feasible. ful probability assessment. Taxon phylogenies fall Sometimes very convincing stratigraphical distribu- out of such Darwinian analysis and render the tions of abundant data dramatically demonstrate former far more probable than an axiomatized and how attempts to shoehorn such evidence into the abiological parsimony search for the congruence of prescriptions of cladistic analysis distort a phylog- often atomized traits of various taxa. eny when segments of lineages are forced into ”terminal” species taxa to conform to cladistic prac- ON THE ROLE OF TRANSFORMATIONAL tice. This was dramatically and painstakingly dem- ANALYSIS OF PROPERTIES, AND THE onstrated by Redline (1997) in his rigorous MEANING OF MOSAIC EVOLUTION IN stratigraphically controlled study of the largely PHYLOGENETIC ANALYSIS Wasatchian (North American early Eocene) small mammal, the condylarth Hyopsodus. Such infor- Literal transformation is in the realtime of an mation (and astute analysis) is often rare at the individual organism only, its entire ontogeny; it is population or taxonomic species levels, but the not what is meant by evolutionary transformation. context of biostratigraphical information is critical, ”Universals” having to do with development, even even if problems and analysis are at a higher level, the immensely deep homologies (orthologies) of removed from species taxa. hox-genes are contingency bound. They are there- Beyond the best estimate of phylogenetic fore subject to historical understanding, not just to topology for the groups of organisms studied, an rules that consider some developmental attributes important goal of taxonomy (in keeping with Dar- universal or to the methodology of parsimony algo- winian aims) is to strive for properly demarcated, rithms. Darwinian phylogenetic analysis is a histori- monophyletic taxa diagnosed by apomorphies of cal narrative method to attain contingency-based their stems with the clear understanding that the explanations, and it represents the combination of base delineation must depend on both the avail- several research programs, not just morphological ability of information and some heuristically mean- approaches. Darwinian phylogenetics addresses ingful sense. The unsuitability of the Linnean the issues of contingency and adaptation that can- system for evolutionary depictions, created at a not be isolated from one another when we seek to time when non-evolutionary and atemporal sorting understand phylogenetic transformations of was the aim of taxonomy, has been often dis- attributes and lineage reconstructions. cussed in spite of its suitability for punctuationism Spatio-temporal and functional factors sur- and taxogram views of evolution. The continuity of rounding morphology provide the grist for the mill evolutionary lineages and the inability of the Lin- of phyletics in character analysis. Both the phylet- nean system to deal with time make taxic analysis ics and cladistics of taxa depend on these. Rapid of phylogeny flawed from its very inception (but for advances in developmental genetics, the under- some recurrent suggestions for fossils see Redline standing of modularity in the developing organism, 1997). In taxic analysis, taxa are considered the and a concerted use of functional and ecological starting point for both the phylogeny of the taxa biology, together with a fossil record, can play a themselves and, subsequently, for the understand- critical part in this approach that has to be tailored ing the polarity of traits. This is a fundamental tenet both to the groups analyzed and the levels at which of most parsimony-based cladistics. Nearly invari- it is employed. However, ”ultrafunctionalist” per- ably, these views are tied to an ontological concep- spectives on adaptations (e.g., some gene-selection of species (which are in reality species taxa) tionist, sociobiological, explanations) , in which through time. Ontologically a species in a moment cost-benefit evaluations and a lack of historical of time is a segment of its lineage, and only extant perspective dominate, are not concordant with Dar- representatives are unequivocally terminal, win’s own history-guided understanding of adaptive although undoubtedly millions of lineages became 22 evolution. extinct. Nevertheless, those practicing taxic analy-

14 F. S. Szalay: Function and Adaptation in Paleontology sis base their ideas of a species taxon on the con- "hoary old concept" in order to drive arguments ception that species and other taxa are against the straw man of transformationism in sys- ”individuals”.23 These same systematists also tematics are unfortunate. Such views are particu- often oppose the transformational analysis of taxo- larly surprising in light of the increasing evidence nomic properties in systematics and argue for the from developmental biology that modularity(and decoupling of phylogenetic analysis from evolution- the often striking independence of the modules ary theory (e.g., Rieppel 1993). The result is an within the same organism) is very probable.26 It is advocacy of methods based on a structuralist the- a mistake to believe that natural selection cannot ory of evolutionary transformation that is wedded to favor individuals that retain some attributes that and derived from the practical procedures of delin- continue to interact with selection in an unchanged eating species and other taxa. Such efforts invari- manner while these same individuals have new ably yield theories that selectively mix the characters that fulfill other aspects of their adapt- conceptual foundations of tested evolutionary edness. Any argument against the phenomenon of dynamics with epistemic criteria and notions mosaic evolution not only betrays too much reli- derived from the latter. Consequently, such theo- ance on outdated concepts of epistasis, but it also ries are simply epistemic, without ontological foun- misses fundamentally pattern-based observations dations and provide inadequate conceptual about taxa. methods for character analysis. Adherents of parsimony-based cladistics or Systematists who reject transformational anal- punctuationism, whether they are against transfor- ysis also usually adhere to the notion that there is mational analysis or against the observationally something causally and processually distinct in the based concept of mosaic evolution, often inadvert- origin of a new lineage (speciation) and its perse- ently reject some of the great advances of both verance from anagenetic (= phyletic) evolutionary Darwinian evolutionism and the Modern Synthesis, change itself.24 They realize that transformational yet they also strive at the same time to accommo- analysis poses a core disagreement with the tenets date the centrality of adaptation. The facts that of hierarchic punctuationism, a fundamentally taxic functionally and adaptively highly-correlated (and speciational) view of evolution. Yet such a dis- attributes of one character complex may have agreement is minor. The conceptual step needed remained stagnant (e.g., due to stabilizing selec- to acknowledge is that the real history of lineage tion), whereas others have evolved in various continuity and splitting appears jagged due to directions (even in populations of the same spe- extinction and the missing fossils of the variably cies), attest to the differential adaptedness of differ- evolving lineages. Only unwarranted assumptions ent lineages. Students of speciose groups of about species (lineages) and the artificial gaps in vertebrates know well that, although some the fossil record permit a fully taxic view of the evo- attributes are species-specific, other complexes lutionary process. Punctuationists and cladism- can remain virtually identical at higher taxonomic based taxonomic theorists have had a long history levels. It has been repeatedly corroborated that of sidestepping the issue of transformation, but aspects of taxa evolve at different rates (Simpson their real problem is with the concept of anagenetic 1953). It has also been noted that often chronolog- change in lineages.25 Anagenetic transformation is ically older adaptations contain the structural and an obvious impediment for those who want to have functional limits needed for new behaviors, and a causal macroevolutionary evolutionary theory in therefore these older complexes do not evolve sig- which taxa, the “individuals,” do the evolving. Pop- nificantly for long periods of time. Equally prevalent ulations and species evolve, lineages are their are some well-established structural adaptations record, and there are no theoretically meaningful that simply channel the relevant functions associ- boundaries in time-successive realtime popula- ated with newer roles. tions/species to satisfy taxonomic conventions. As examples of mosaic patterns, the attain- Delineations of time-successive species taxa are ment of functionally well-honed stages in the necessary, but they do not, by themselves, inform metapodials (as well as the carpals and tarsals) of about the nature of the evolutionary process itself different genera of perissodactyls, artiodactyls, or in undivided lineages. As a result of this theoretical the universal modification of the first phalanx of the conflict, an expanding Synthesis stands in the way first ray of the foot of all bats to be approximately of taxic and hierarchic punctuationists who want to 1.5 times longer than the equivalent units lateral to weave another evolutionary theory from taxic oper- it (probably for an ancestral tail-hook landing tech- ationalism (Szalay 1999a). nique connected with the attainment of flight; see Linked attacks on the phenomenon of mosaic Szalay and Lucas 1993) did not prevent a riot of evolution, a genuine pattern description, as a cranial and dental, and a plethora of other evolu-

15 F. S. Szalay: Function and Adaptation in Paleontology tionary differentiation within these groups. How times compelling fossil record of successive fossils could we contemplate the recovery of phylogeny if samples of the same kinds of organisms? As it were not for the persistence of homologous simi- briefly outline in this paper, the Darwinian context larities of varying antiquity?27 Highly and causally of lineage transformation sets the boundaries corroborated correlations of homologies and syna- within which the contingent attributes of different pomorphies in different lineages attest to the fact lineages at all time levels, or stages of the same that the phenomenon of mosaic evolution is a cor- lineages, may be recognized and weighted as nerstone of an independent transformational analy- being either more probably homologous or sis of traits, in contradistinction to taxon-driven, and homoplasious. Practitioners of mathematical lin- most often parsimony-driven, "transformational" earity as a substitute for biological and paleonto- analysis. Whatever the rate of evolution of such logical analysis - and who, as a rule, do not order events, hundreds of examples may be cited from and polarize the characters they use without algo- the patterns of vertebrate taxic diversity.28 Even rithms - eschew the need for a conceptually inter- episodic changes are gradual because gradualism disciplinary and Darwinian context for character in the Darwinian sense is rate-independent (see analysis. Parsimony-based cladists customarily Simpson 1953). rely on diverse databases without any causal input Taxonomy reflects the painstaking and only into the selection of these traits and employ algo- partially recovered evidence of evolving lineages rithm-driven congruence to order and polarize and their diversity at any time. It is a result of efforts characters. They claim to follow such linear prac- to construct meaningful taxonomic species and tices in order to fulfill the need for notions of ”con- somehow express their relationships in higher sistency” and ’scientific’ (= Popperian) monophyletic taxa in order to gauge organic diver- respectability for the testing of what is in fact a sity and to provide the necessary heuristics for the highly idiosyncratic and mosaic manifestation of study of the history of life. Fossil-species taxa are lineage choreographies of evolving species and not reliable equivalents of modern species, which speciation events, phenomena that do not corre- can be delineated by their reproductive discontinu- spond with paleontological species taxa. They ity in contrast to other species. They are certainly hold, for all intents and purposes, that a tested dis- not all ”terminal taxa.” Rather, fossil species are embodied ”genealogy” of taxa can be attained with- estimates devised by trained taxonomists and out an understanding of the factors responsible for based on selected models of extant species that the properties of organisms. have been well studied regarding their geographi- The following major points are a brief sum- cal distributions, attributes, and sometimes genet- mary of some aspects of these issues, which are ics, as well as the various forms of intergradations discussed in the body of the paper in some detail. of their populations (Jolly 1993; Szalay 1993; vari- 1. What phylogeny (but not classification) is has ous papers in Kimbel and Martin 1993). These fos- bearing on how we should try to recover it. sil species taxa are certainly not all new lineages Descent with ancestrally constrained (but also but many undoubtedly represent lineage seg- facilitated) adaptive (and other) modifications, ments, as all taxonomic species do. This notion of largely through natural and sexual selection, taxonomic species also applies to living-species contains a host of post-Darwinian advances in taxa that often incorporate samples of precedent evolutionary biology that relate to this funda- populations of varying antiquity. mentally Darwinian view of the evolutionary process. This complex array of precepts is CONCLUSIONS AND SUMMARY both the theoretical foundation of a Darwinian As recently stated by Gingerich and Uhen phylogenetic analysis and the basis for any (1998, p. 3), "Evolution is first and foremost a his- comprehensive theory of function (in a broad tory of ancestors and their sometimes-divergent sense) and structure. Meaningful functional descendants." This is a Darwinian generality that (in a full Darwinian sense) and phylogeneti- has profound consequences for estimating the cally oriented biology is the study of the evolutionary history of all organisms, but one that is results of selection and other attributes, and of often ignored by systematists who practice a taxo- the process of their acquisition. gram approach. 2. Fundamentally structuralist approaches con- The obvious question is, what are the guide- sider the goals of adaptational and other evo- lines or parameters that circumscribe and inform lutionary analysis to be unattainable for fossils transformational or polarity determinations of char- and extant organisms. Yet adaptations or sex- acters and the relationship of taxa beyond a some- ual-selection-related paraphernalia in extinct

16 F. S. Szalay: Function and Adaptation in Paleontology

species are often better understood than their tive explanations or their rigorous tests deal- phylogeny. Such attributes may form the ing with adaptations or phylogenetic estimates framework of an analysis. A functional and of character transformations. These activities adaptational (ecologically utilitarian) assess- are the core of comparative biology and mac- ment of traits in both extant and extinct organ- roevolutionary science, and the testing of phy- isms (whenever possible) is necessary in logenetic hypotheses of lineages and taxa order to reliably establish polarities of homolo- fundamentally relies on them (Figure 1). gous features. Such practice enables stu- Organisms are adapted (= ”fit,” in a fully Dar- dents of phylogeny to cull convergent winian sense) and an understanding of selec- attributes from a body of characteristic fea- tion-produced attributes (e.g., mechanical tures. The Darwinian method, contrary to mis- adaptations or dimorphisms) can have a sig- construed characterizations that it permits nificant influence on choosing features only the use of adaptive characters in phylo- against which phylogenetic estimates can be genetics (e.g., Schuh 2000), informs of the tested. Thus, functional understanding is incidental and phyletically relevant attributes essential in any estimation of phylogeny. in assessing the adaptive solutions. The Model-based analysis of attributes of selected homologously shared and derived, or transfor- extant species is a cornerstone of this activity. mationally homologous, features so obtained 5. Taxograms, bereft of specific taxic derivation are the taxonomic properties against which (origins), do not reflect the lineage-based real- lineage and taxon phylogeny hypotheses may ity of phylogenetics. Axiomatized attempts to be tested. reflect the history of organisms as taxograms, 3. A Darwinian evolutionary explanation involves node-based holophyla, without paraphyla is both the causal and historically mediated an illusory practice. It is contradicted by the components of a particular transformation, an continuity of all lineages in the evolutionary evolutionary becoming. Its macrotaxonomic process, and the necessity to make arbitrary expression is constrained by heuristics, which demarcations when delineating taxa. are not directly relevant to phylogenetics. A In closing, I note that the attempt at the expur- sharp divide between functional and evolu- gation of the fully Darwinian (= adaptive) context of tionary explanations, distinction are more evolutionary change from both conceptual and practice-based than theory-based. These operational methods has been largely driven by a should be replaced by a less dichotomous, belief that analysis of patterns independent of less hierarchic, and far more interrelated or tested evolutionary theory will yield a theory of evo- ”temporally looped” set of theories and con- lution of such generality, and that this theory will cepts regarding the relationship between the replace an expanding Modern Synthesis (see evolution of function and biorole of features. Eldredge and Cracraft, 1980; Grande and Rieppel, Functional analysis (broad, Darwinian sense) 1994; Rieppel and Grande 1994). Beyond claims and the biostratigraphical record are the valid that Darwin has been reinvented (Eldredge 1995; bases of transformational analysis of organis- and in this process, not coincidentally, omitted from mal attributes in phylogenetics (Bock 1981). phylogenetics) and the rise of a hardened taxic The results of the transformational analyses of paradigm of parsimony-based cladistics, nothing of features and the subsequent understanding of the sort has materialized thus far. the relationships of lineages, independent of parsimony taxograms, are prerequisites for a ACKNOWLEDGMENTS meaningfully tested taxon phylogeny. Both adaptational and phylogenetic analyses are While we disagree on some theoretical points, inferential about specific events in the past. it is from W. J. Bock that I learned as a graduate Mapping the results of the ”causal role func- student to appreciate the importance and subtleties tion” approach of Lauder and colleagues onto of a functional-adaptive perspective in phylogenet- taxograms, a structuralist perspective that is ics. Our long friendship has been a constant now labeled by its practitioners as the “new source of inspiration for me. Bock is the foremost adaptationism,” does not advance the cause living champion of what may be considered a Dar- of phylogenetic reconstruction. winian approach to the analysis of evolutionary history. Although he considers to refer to this practice 4. In spite of the obvious data-based limits of the of systematics as an evolutionary one (he has in past that were previously noted, there is no fact brought exceptional new theoretical strength to reason to reject either specific historical narra- it), I prefer the Darwinian appellation. Most high-

17 F. S. Szalay: Function and Adaptation in Paleontology profile evolutionary systematists in the past have by the definition of “Mammalia.” Systematic Biol- not followed rigorously a methodology that is inher- ogy, 43:497-510. ent in Darwinian precepts of adaptive evolution. De Queiroz, K., and Gauthier, J. 1990. Phylogeny as a My thanks to J. Warshaw who prepared the central principle in taxonomy: phylogenetic definition schema on Figure 1. I am also grateful to N. of taxonomic names. Systematic Zoology, 39:307- 322. MacLeod, E. Sargis and J. Warshaw, who made De Queiroz, K, and Gauthier, J. 1992. Phylogenetic tax- many useful stylistic suggestions. onomy. Annual Review of Ecology and Systemat- ics, 23:449-480 REFERENCES Eldredge, N. 1995. Reinventing Darwin: The Great Amundson, R. 1996. Historical development of the con- Debate at the High Table of Evolutionary Theory. cept of adaptation, p. 11-53. In Rose, M. R., and John Wiley & Sons, New York. Lauder, G. V. 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20 F. S. Szalay: Function and Adaptation in Paleontology

NOTES nig, contrary to suggestions by Haszprunar (1998). This does not mean that Hennig’s contribution has been 1. See, for example, Schuh’s (2000) textbook unimportant to modern phylogeny estimation. It should on cladistics. be obvious to anyone reading Hennig that he was inter- ested only in using synapomorphies that were biologi- 2. In a theoretically rigorous sense Szalay and Sargis cally convincing to him. The notion of having an (in press) see bone tissues and skeletal structures as a algorithm decide the fate of similarities as being either complex expression of the genome that reflects the inter- homologies or homoplasies is a post-Hennigian inven- action of ancient phylogenetic history as well as its real- tion based on the methods developed by the school of time environment. Both tissues and whole bones are phenetics. primarily entities with attributes also strongly channeled by developmental (ontogenetic) history. Growth rates 5. For all practical purposes the realtime (not to be and other organizational parameters in the genome, cou- confused with the meaning of real time) of individual pled with the level of homeostasis, endocrinology, and organisms is the length of their life. In neontological loading due to activity patterns and size, become the practice, however, realtime also stands for a short final arbiters of both bone shape and microstructural tis- stretch of population and species duration. So realtime is sue attributes. Ancient gene homologies reflect the the frame of duration for a) either the living organisms expression along a range of these gene-environment that are subjected to the causes that shape an evolving factors. All genetically mediated aspects of this organiza- entity such as a population or species to which the tion are guided by ecology (selection) through geological organisms belong, or b) for the species-populations, the time. A holistic understanding of the specifics of such "instantaneous" segments that are doing the evolving systems is one of the least trivial aspects of the science compared to antecedents stages. The concept of real- of form. time for specific populations and species, of course, can 3. Much of the systematic literature of the last decade rapidly become both a theoretical and empirical greased has focused on the categorization of abstract models of pig (Szalay 1999a). phylogenetic-cum-taxon patterns. The terminology to 6. I believe that this was a red herring, as no one I describe the various axiomatized taxonomic patterns of know thinks of preadaptations as teleological. A similar taxograms and an ongoing redefinition of these concepts characterization of adaptationism is often employed in (e.g., DeQueiroz 1992, 1994; DeQueiroz and Gauthier discussions of ”causal role functions,” namely that an 1990, 1992; Rowe and Gauthier 1992; Sereno 1999) has adaptationist perspective is somehow ”teleological.” reached a state of rococo confusion, as is evident from 7. The whole issue of a variety of straw-man per- Sereno’s (1999) instructive review and his tabulated list spectives on adaptationism cannot be commented on of definitions (although he continues to add to this list). In here in any meaningful way. This topic has been pursued addition to definitions, the specter of a straw man of the using some of the most absurd argumentation, substitut- essentialistic perspective was also raised and misunder- ing monotonic (and, to some, convincing) argumentation. stood by DeQueiroz (1994) in order to justify this curious For example, Lewontin (1978), one of the most vocal debate of abstractions. It is ironic, therefore, that after critics of ”adaptationism” (as defined by him) of the past the extensive and sometimes surreal literature it should several decades, has even been quoted as one of the become obvious again that taxonomic expression with- champions of Darwinian sobriety! Novacek (1996, p. out heuristics is an activity that creates confusion and 314), walking the tightrope of ”balance”, notes that does not serve the larger community (Szalay 1999b). As “[I]ndeed, Lewontin (1978) and Gould and Lewontin Sereno (1999, p. 350) concludes, “Survivorship, diver- (1979) have argued that functional morphology flirts with sity, morphology, and tradition are heuristic criteria for the untestable; an adaptive explanation that fails is often placement of node-stem triplets.” The issue of “stems” as substituted with another explanation rather than rejecting real evolutionary units (and therefore potentially real taxa the basic premise that the system under observations if we knew of them and they were given taxonomic demands explanation” (emphasis added). This is inter- expression) is a complex one that has relevance for the esting because, when a phylogenetic hypothesis is monotonic notion of ”unreality” of paraphyla. Novacek proven untenable, Novacek or any of us certainly do not (1996, p. 340) is not alone when he notes that paraphyl- abandon the premise that phylogeny did occur, but etic taxa “are not credible biological entities.” What this rather we go on to find one that fits the available informa- means, of course, is that based on a chosen (and deeply tion better. But more to the point are Lewontin’s (1978) flawed) taxonomic ontology regarding ancestral biologi- statements that “if ecological niches can be specified cal entities, the real stems of various groups should be only by the organisms that occupy them, evolution can- axiomatically barred from taxonomic recognition. The not be described as a process of adaptation because all best estimates of such stems are often genera in the fos- organisms are already adapted” (p. 215) and that sil record. “[a]daptations are not necessary conditions of the exist- 4. The conceptual roots of modern phylogenetics, the ence of the species…” These notions are capped with combination of descent and adaptive modification, are the observations that although the fur of polar bears is an fully Darwinian. They have not been derived from the adaptation (because otherwise they would freeze to theoretically reformulated and somewhat truncated, death), the adaptive meaning of its white color is ques- more recent versions advocated by Remane and Hen- tionable. I simply note that if ptarmigans, snowshoe

21 F. S. Szalay: Function and Adaptation in Paleontology hares, arctic geese, and polar bears have white color as very little on adaptation), these authors speak of the a property, then this coloration is far more plausibly an “rise” and subsequent impetus of cladistics and the “new adaptively essential camouflage than a “just-so story,” as adaptationism.” While they and others speak of “rigor” it is asserted to be. This is an overwhelmingly probabilis- regarding interspecific comparisons (e.g., Harvey and tic and corroborative testing of a proposition, deduced Pagel 1991), they omit critical theoretical issues. They from the most basic ecological theory of competition overlook the fundamental importance of an ancestral enunciated by Darwin. Although without a doubt not all condition-centered phylogenetic tree for all valid non- the specifics of evolutionary change are adaptive in the independence methods (cf. McMahon 1999), such as history of life, that does not mean that the process is not those concerned with analyzing adaptations with statis- fundamentally selection-mediated. In fact monotonic tics in multiple lineages. The output of parsimony cladis- logic (and agendas), as the literature and quotations tics devoid of causally meaningful ancestral here suggest, are part of an effort to underplay the core reconstruction is not amenable to such efforts. role of Darwinian selection in the evolutionary process. 12. The structuralist bias of Lauder (1982, p. 57) is These are the major underpinnings of the celebrated well reflected in one of his early contributions: “The syn- attacks on the straw man of ”adaptationism” by Gould thesis of a structural/phylogenetic approach to historical and Lewontin (1979). morphology with the analysis of extrinsic limits to form 8. Mahner and Bunge (1997) have a problem consid- may provide the level of resolution needed to generate ering events in ontogeny as causal. I prefer to consider testable mechanistic hypotheses regarding the distribu- all events in the realtime of an organism genuinely tion of extant organismal forms in the hyperspace of pos- causal. Events in ontogeny have consequences well sible morphologies.” The adaptational vacuum is beyond the unfolding of the genetic blueprint or the heri- evident, the functional prescription is non-Darwinian, and tage of the zygote. the theoretical position is totally concordant with the paradigm of taxogram-generated cladistics. 9. The resultants of past causes simply manifest themselves as the constraints that will guide the unfold- 13. “Multidisciplinary” merely means that previously ing of the zygote, with its cellular contents, context, and the components of a research program represented dis- included genotype, in the epigenetics of development or tinct disciplines. even in an individual’s “culture” (nongenetic transmitted 14. Unfortunate and inappropriate uses of monotonic predilections among organisms) in realtime. In some logic are Gaffney’s (1979) and Wyss and Flynn’s (1993) ways the genotype and its zygote-based context repre- stances on character transformation. Their representa- sent the distillation of the past evolutionary history of an tive views reflect the taxic perspective on a caricature of organism, and therefore the causes in the history of lin- ”character transformation.” This taxic practice attempts eages are inseparable from real constraints that are to render illegitimate the cornerstone of evolutionary parts of the initial and boundary conditions for any organ- understanding, namely comparative analyses of homolo- ism in its realtime. So “ultimate” causes as such are part gous character complexes in their own adaptive context. of the admittedly difficult conceptual area of constraints Parsimony-based cladists who do not order and polarize and are not real causes. There are, therefore, only proxi- their characters, consider character transformations mal and more distal causes that affect the individual merely corollaries of taxon-phylogeny hypotheses. Such organism during its life history in its realtime existence, efforts, in light of the modularity of functional complexes and these have evolutionary consequences for its popu- in organisms, are particularly egregious even when func- lation or species. tionally well-understood complexes are ”mapped” onto a 10. Ultrastructuralists who hope for a universal sci- previously generated taxogram for a different region of ence of form miss, I believe, the full meaning of phylog- the organism. For example, even if a cladogram of cra- eny. The descent of differentially successful ontogenies nial and dental characters were true, superimposing should indicate that because of the differences, and not postcranial traits on it does not necessarily render the because of their universality, ontogenies succeed differ- transformational history of that mapped complex mean- entially through time. The historical and adaptive pro- ingful. The demands on and consequences of selection cesses that Goodwin (1994, for example) tries to are different for different aspects of organisms (see marginalize are an obvious threat to any neo-Platonic later). In using monotonic logic instead of biological universality that he attempts to deduce from the com- sleuthing, a taxic perspective also implies that the evolu- plexity of the structural transformation of embryos. The tion of all character in lineages is bound up in the con- commonality of patterns and processes of organization certed, orchestrated, and magical origin of species taxa are not transcendental truths but the footprints of a phy- through speciation. Punctuationism, even if many cla- logeny. For another extreme structuralist perspective by dists profess disdain for any evolutionary theorizing, is someone who, in addition, considers Darwinism a repre- obviously implicated here. hensible theory, see Salthe (1989, 1993). 15. The philosophical literature on that one topic alone 11. In the significantly titled “Post-Spandrel Adapta- is enormous. Most of it is marred by a syllogistic presen- tionism” by Rose and Lauder (1996) and the introduction tation of issues about trait, function, and organism and to their edited volume on adaptation, which strongly the omission of the time-sequential nature of the work- reflects their particular perspective on phylogeny (and ings of selection. As a consequence, there is the lack of

22 F. S. Szalay: Function and Adaptation in Paleontology realization of the shifting base of what the features and and that selection is everything. I don’t think anyone roles are from generation to generation; or a customary believes this, although the anti-selectionists usually see lack of consideration of selectionally mediated, direc- it as necessary to construct a false target to attack.” tional, form-function changes for the same biological 18. The recent book by Gee (1999), senior editor of roles that are the core of Darwinian progress. Nature, is an example of a popular version of the taxo- 16. Bock (e.g., 1999) eschews the assessment of gram approach to phylogenetic estimation that is devoid adaptations without previous mechanical analysis and, of the paleontological method and character analysis. In therefore, implicitly rejects the proven value of correlat- stating, for example, that: “[w]hat we need is an antidote ing carefully selected variables in morphology with to the historical approach to the history of life–and kind of shared bioroles and ecological factors. That is unfortu- ‘anti-history’ that recognizes the special properties of nate because the latter is the powerfully predictive con- Deep Time” (p. 5), Gee reached the zenith of a move- vergence method. For example, detailed biometric ment that fully embraced Popper and subsequently comparisons of osteological parameters of diversely denied that induction exists or that it is important. In his adapted and unrelated species will often result in highly railing against the comprehensibility of deep time and instructive clusters of both divergent and convergent paraphrasing the often-implied spirit of some of S. J. complexes that can be strong indications of similar adap- Gould’s writings, specifically that trends and their Dar- tations, and/or multiple solutions for similar roles (e.g., winian progressive explanation in the fossil record are Stafford 1999). Numerous carefully selected compari- really “… misleading tales …part of popular iconography sons based on massive samples and carefully derived …” (p. 5) Gee provided insight into the irrational physics- indices result in valuable correlations that are often envy of a large part of the systematic community. This proved to be causal regarding certain bioroles. Such cor- book, praised only by a few paleontologists, is really not relational statistical studies often pave the way for more about the scientific significance of the geological and focused functional analyses. In general, attempted theo- paleontological record, in spite of its paleontological pre- retical cubbyholing of dynamically inseparable evolution- tensions. The smugness of the half-truths and rhetoric of ary issues that grow out of search for increasingly this book is permitted by the overwhelming disregard by complete explanations are doomed to be reconstituted. the author for the connections of evolutionary theory to taxonomic practice, a Kuhnian team perspective that has 17. Studies such as Benton (1987), Hulley et al. been rigorously enforced by the cladistic movement of (1988), Masters and Rayner (1993), Rayner and Masters the past several decades. More specifically, the assump- (1995), and Walter (1988), for example, suggest or tion that theories about evolution should be based on the assert that the Darwinian imperatives of ecological com- taxic perceptions of taxonomists has supplied a hollow petition are somehow not reflected in ”objective” analy- authoritative tone that is based on the pattern-process ses of the fossil record or community structure and that paradigm. Gee’s claims that deep-time, historical narra- variance-shifted punctuated trends (Vrba 1980; Gould tives (“evolutionary narratives,” as he called them, but in 1988) are substitutes for most explanations of evolution- the pejorative tradition of spandrelism) are all either ary progress driven by directional selection. Like many incomprehensible or human-biased (i.e., nonscientific). such studies, these attempt to marginalize the critical He asserts that all should adopt the parsimony-based importance of Darwinian selectional dynamics in evolu- cladist’s perspective of merely seeing patterns rather tionary explanations. Not a few of such contributions are than what he considers the unknowable evolutionary strongly driven either by political ideology or social process responsible for these patterns. Gee’s book is a dynamics, or by a combination of both (see a review of telling exemplar in what can happen to theory and prac- the role of paleontology in macroevolutionary dynamics tice in paleontology in the hands of Popperian system- in Szalay 1999a). The geneticist Hurst (1998, p. 50-51) atists. noted regarding a number of books (by M. Behe, S. Kauffman, S. J. Gould, B. Goodwin, N. Eldredge, and S. 19. I disagree with Galis (1996, p. 124) that transfor- Rose) that: “[a]lthough anti-selectionists often have little mational analysis is “a new approach in functional mor- in common (except a preference for seeing selection phology.” Furthermore, her example of bat relationships downgraded in the public imagination), I have noticed regarding micro- an macrobats is fundamentally flawed one strange regularity. They all belong to what I shall call for the simple reason that the skeletal morphology is not the ‘c’ club. Entry to this club requires a member to adopt considered with any kind of functional and phylogenetic a word beginning with ‘c’ with which to attack selection- understanding. Galis’s treatment is similar to Pettigrew’s ists, if only by obfuscation. Evolution is constrained, cha- original suggestion, in a series of papers (e.g., 1986), otic, catastrophic, contingent, or complex (irreducible or that the two groups are “independently” bats. Galis’s the- otherwise). My main problem with these books is that the oretical approach mirrors the ”causal role function” per- ratio of assertion to fact is too high … Worse still, asser- spective of Lauder and others, omitting a historically tions are often sold as facts with the merest peppering of constrained adaptational analysis from her theoretical anecdote to support them … Gould’s use of the word prescriptions. ‘constraint’ and ‘contingency’ have, for example, left a 20. “We may err in this respect in regard to single mess of confusion that has generated a sterile mini- points of structure, but when several characters, let them industry in semantics to clean up after him. Of course it be ever so trifling, occur together throughout a large would be wrong to suggest that evolution is all sorted out group of beings having different habits, we may feel

23 F. S. Szalay: Function and Adaptation in Paleontology almost sure, on the theory of descent, that these charac- causally different aspect of ”new species” (Szalay ters have been inherited from a common ancestor. “(Dar- 1999a). win 1859, p. 426; emphasis added). Note the decisive 25. A recent instructive example regarding this theo- reference, the ecological context, included in this state- retical effort is Nixon and Wheeler’s (1992) view of the ment by Darwin. It is not merely the sharing of charac- ontology of ”species.” Without discussing their thesis ters, but the ruling out of convergence due to divergent (see Szalay 1999a), they stated that “Finally, from the habits, which makes such correlated and aggregated standpoint of phylogenetic species concept, character characters (to paraphrase Darwin) genuine traits of com- transformations always produce new species, so mon unique heritage (i.e., synapomorphies) in different anagenesis cannot occur within species …” (p. 136; taxa. The opposite but ancillary rule of this tenet, the emphasis added). This interesting attempt to equate tax- convergence method, is that shared characters (but not onomy with evolutionary theory is merely one example of whole complexes or major attributes) of animals corre- the nature of contributions in which the wedding of punc- lated with similar activities or habit (habitus) should be tuated chunks and invariant taxa supply the “objective” suspected as convergent. Functional-adaptive explana- patterns of the history of life and a distorted view of evo- tions of phenotypic strategies are the key to analyzing lutionary ontology. what the similarities and differences mean in terms of the phylogeny/adaptation continuum in a real ecological con- 26. Recent work on the nature of functional integra- text (one that is model-based in paleontology). So the tion, because this involves both modularity as well as solution of this dilemma is the consideration of the adap- heterochrony, at least in the skeletal system (Raff 1996; tive context prior to choosing phylogenetically meaning- Smith 1996, 1997; Nunn and Smith 1998; and refer- ful attributes. Whereas Darwin understood that the ences therein), strongly support older ideas that parts of meaning of phylogenetically significant attributes is hid- bodies are modularly controlled by both the developmen- den in an adaptive package that has to be unwrapped tal system and the evolutionary process itself. with the aid of sound methods derived from evolutionary 27. I am not aware of any evidence that humans were theory, too many other systematists who followed, most other than bipedal for at least the last two (and probably recently parsimony-based cladists, failed to consider this three or more) million years, yet our thorax and shoulder theoretical stricture. and elbow joints are not significantly different from a bra- 21. Conceptual methods should fall out of tested the- chiating knuckle-walking ancestor that obviously pre- ory. Workers advocating a taxic version of the evolution- dated the one we probably descended from. So, our ary dynamic (perhaps the handle “taxism” is not entirely upper body is a mosaic compared to the quite thoroughly out of place for that perspective) conveniently ignore this and more recently reconstructed pelvic limb; it is an area general dictum, namely that the valid methods of phylo- rich in homologies connecting us with the great apes. genetic analysis of taxa should fall out of the underlying Subsequent to bipedality in hominids, the pelvic limb did tested mechanisms of the evolutionary dynamic (popula- not change significantly for at least the past million and tional, developmental, and functional) and not out of its half years (or more). In spite of such modular stasis, shifting taxonomic perceptions. many other changes did occur in sundry segments and various evolutionary units (populations) of our lineage. 22. “Historical” explanations in sociobiology tend to be Taxic reconstructions of hominid phylogeny would have patently ahistorical, and therefore flawed (see the cri- up to 12-15 taxonomic species implying speciation tique in Szalay and Costello 1991). events and closed lineages. Yet the corroboration of 23. I do not accept the notion that taxic individuality is more than two (or possibly three) bushy lineages through the proper and decoupled way of looking at evolutionary lithosympatry does not exist. Hominids are a perfect and dynamics, as characterized in doctrinaire cladism and high-profile example of the failure of cladistic, OTU- hierarchic punctuationism (Szalay 1999a, 1999b; see driven (i.e., operational taxonomic unit-driven) attempts also Mahner and Bunge 1997, and their total rejection of at the reconstruction of evolutionary history. The spe- bionominalism; and Bock’s in press detailed rebuttal of cies-level misapplication of the taxogram paradigm gives Ghiselin 1997). The ”essentialistic class” versus “individ- a distorted history, in contrast to a reasonable strati- ual” dichotomy applied to the phenomena of life is an graphical control, a fossil record, and meaningfully cho- outdated, originally ancient Greek, metaphysics that was sen extant models that set the limits of evolutionary simply not applicable after 1859, in spite of Ghiselin’s understanding. Ongoing and repeated arm waving not (1997) brilliant but quixotic effort. The discovery of varia- only about how speciose the family was, but also by tional evolution by Darwin and Wallace has changed the implications about how many independent lineages nature of a valid metaphysical perception of the world, came to be during hominid evolution have repeatedly particularly of species and other aggregate biological failed to demonstrate the synchronous co-occurrence of phenomena. Evolutionary units are not individuals. acceptable species-level lineages other than the robust and gracile hominids. 24. Speciation certainly results in a new and eventu- ally genetically isolated lineage, a significant major event 28. Carroll’s (1997, p. 2) attribution of the notion of in diversity and overall phylogenetic pattern, but this “constancy of evolutionary patterns” to Darwin, based on mode of the evolutionary dynamics is a consequence of Darwin’s single figure in the Origins, is both inaccurate anagenetic change and (usually) isolation, and not a and sells short Darwin’s complex conceptualization of

24 F. S. Szalay: Function and Adaptation in Paleontology the evolutionary process. It, unfortunately and probably tuationism. Darwin’s understanding of the rate-indepen- inadvertently, reflects the revisionism that punctuation- dence of evolutionary change, in spite of his clear ism has ushered in. That simple iconography does not adherence to gradualism (i.e., contra the saltationist begin to reflect Darwin’s views on rates of evolution; Dar- views of his contemporaries), has been amply corrobo- win was not a “rate-dependent gradualist,” in spite of that rated numerous times (Szalay 1999a, and references straw-man wrapping created for him by hierarchic punc- therein).