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 working 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 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. Transformational 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.
Frederick S. Szalay. Departments of Anthropology, and Ecology and Evolutionary Biology, City University of New York; Hunter College, New York, New York 10021, USA.
KEY WORDS: Function, mechanical analysis, adaptational analysis, Darwinian phylogenetic analysis, parsimony cladistics, mosaic evolution.
Copyright: Society of Vertebrate
Paleontology, October 2000
Submission: 6 July 1999, Acceptance: 29
August 2000