Transformed cladistics, also known as pattern cladistics, is an epistemological approach to the cladistic method of phylogenetic inference and classification that makes no a priori assumptions about common ancestry. It was advocated by Norman Platnick, Colin Patterson, Ronald Brady and others in the 1980s, but has few modern proponents. The book, Foundations of Systematics and BiogeographyWilliams, D. M. and M. C. Ebach. 2008. Foundations of Systematics and Biogeography. Springer Science+Business Media, New York. by David Williams and Malte Ebach provides a thoughtful history of the origins of this point of view.
Patterns vs. processes The traditional approach to cladistics, which traces back to Willi Hennig,Hennig, W. 1950. Grundzüge einer Theorie der phylogenetischen Systematik. Deutscher Zentralverlag, Berlin.Hennig, W. 1966. Phylogenetic systematics. University of Illinois Press, Urbana, IL. groups together organisms based on whether or not they share derived characters or character states that are assumed to be descended from a common ancestor. Transformed cladists maintain that the assumption of common descent is uninformative and/or potentially misleading, and that therefore cladistic methods should be free from evolutionary process assumptions, and based only on parsimonious interpretation of empirical data:
In other words, pattern cladists argue that the fewer evolutionary assumptions a classification presupposes, the fewer errors creep in, and greater transparency results. They draw a distinction between patterns, which are observed, and processes, which may be inferred from patterns, but which should not be presupposed. Before the emergence of cladistics as a school, Joseph Henry Woodger criticized phylogenetic systematics on the grounds that homology by way of common ancestry is "putting the cart before the horse, because descent from a common ancestor is something assumed, not observed. It belongs to theory, whereas morphological correspondence is observed.".Woodger, S. (1945). “On Biological Transformations”. In: Essays on Growth and Form. Le Gros Clark, W. E., Medawar, P. B (eds.). Oxford: Clarendon Press. Colin Patterson later wrote similarly:
Pattern cladists, like traditional cladists, think that classifications should be isomorphic to cladograms, recognizing groups based on nested patterns of synapomorphies, but they argue that the discovery of characters is not dependent on apriori considerations about common ancestry:
Nelson & Platnick (1981) also noted that: "all of Hennig’s groups correspond by definition to patterns of synapomorphy. Indeed, Hennig’s trees are frequently called synapomorphy schemes. The concept of ‘patterns within patterns’ seems, therefore, an empirical generalization.” Pattern cladists hence regard synapomorphies to be patterns free of processes.
Criticism A frequent (but false) accusation against pattern cladistics is that its proponents claim that systematics should be "theory free." At some point in the 1960s and '70s pheneticists may have believed that, but pattern cladists are not pheneticists. Obviously, rejecting a priori evolutionary process theories is not the same thing as categorically rejecting "theory" in toto. Furthermore, pattern cladists do not reject post hoc evolutionary explanations for cladograms, they simply think that the evidence is independent of the explanation.Brady, R. H. (1985). "On the independence of systematics". Cladistics. 1: 113-126. Nevertheless, some philosophers with a background conciliatory towards evolutionary taxonomy continue to offer criticisms in this vein:
Of course, the distinction between the phenomenon and its explanation was clear to Darwin: "the grand fact in natural history of the subordination of group under group, which from its familiarity, does not always sufficiently strike us, is in my judgment fully explained."Darwin, C. 1859. On the Origin of Species. John Murray, London, p. 413. But, "“we have no written pedigrees; we have to make out community of descent by resemblances of any kind."Darwin, C. 1859. On the Origin of Species. John Murray, London, p. 425. For pattern cladists, it is not just "any kind" of resemblance, but synapomorphy, that reveals community of descent.
Brady Brady, R. H. (1982). "Theoretical Issues and 'Pattern Cladistics'". Systematic Zoology. 3. 286-291.Brady, R. H. (1985). "On the independence of systematics". Cladistics. 1: 113-126. introduced to systematics the terms explanandum for empirical patterns (the phenomenon to be explained) and explanans for process theory (the explanation), writing: "by making our explanation into the definition of the condition [data] to be explained, we express not scientific hypothesis but belief". In the above quote, Darwin's "fact" is the explanandum; his theory of descent with modification is the explanans.
In this view, whatever the characters imply as the preferred hypothesis of relationships becomes, de facto, "genealogical" when we explain it as a result of evolution.Brower, A. V. Z. 2002. Cladistics, phylogeny, evidence and explanation - a reply to Lee. Zool. Scripta 31:221-223.
Creationist distortion As noted, transformed cladistics does not deny common ancestry, rather it argues a logical precedence: theories regarding processes should only be formulated after patterns are discovered. Creationists have distorted this to argue that there are pattern cladists who are skeptical about whether evolution occurs.
Colin Patterson In November, 1981, Patterson delivered a seminar to the Systematics Discussion Group in the American Museum of Natural History.Patterson, C. 2002. Systematics and creationism. The Linnean 18:13-37. In the talk, Patterson asked provocatively: "Can you tell me anything about evolution, any one thing that is true?", and remarked:
A creationist in the audience taped segments of Patterson's talk to imply he was "agnostic" on the subject of evolution.Colin Patterson: Evolution, Reports of the National Center for Science Education To his dismay, Patterson soon found his name quoted in creationist publications:
(Note that a transcript of Patterson's talk has been published in the Linnean 18(2), and may be downloaded from the Linnean Society).
Modern proponents A notable contemporary pattern cladist is Andrew V. Z. Brower.Brower, A. V. Z. (2000). Evolution is not a necessary assumption of cladistics. Cladistics 16: 143-154 .Brower, A. V. Z. (2018). Fifty shades of cladism. Biology and Philosophy 33: 8 (DOI: 10.1007/s10539-018-9622-6)Brower, A. V. Z. (2019). Background knowledge: the assumptions of pattern cladistics. Cladistics 35: 717-731 (DOI: 10.1111/cla.12379).
References
Additional references Nelson, G. (1985). "Outgroups and ontogeny". Cladistics. 1(1): 29–45. Nelson, G. (1989). "Cladistics and evolutionary models". Cladistics. 5(3): 275–289. Patterson, C. (1980). "Cladistics". The Biologist. 27: 234–240. Patterson, C. (1980). "Phylogenies and Fossils". Systematic Zoology. 29: 216–219. Patterson, C. (1981). "Significance of Fossils in Determining Evolutionary Relationships". Annual Review of Ecology and Systematics. 12: 195–223. Patterson, C. (1981). "The Goals, Uses, and Assumptions of Cladistic Analysis" presented to the Second Annual Meeting of the Willi Hennig Society, Ann Arbor, Michigan. Patterson, C. (1982). "Classes and cladists or individuals and evolution". Systematic Zoology. 31. 284–286. Patterson, C. (1982). "Morphological Characters and Homology". In: Problems of Phylogenetic Reconstruction. K.A. Joysey., A.E. Friday (eds.). Academic Press, 21–74. Patterson, C. (1983). "How does phylogeny differ from ontogeny?". In: Development and Evolution. B.C. Goodwin, N. Holder., C. Wylie (eds.). Cambridge University Press, 1-31. Patterson, C. (1988). "Homology in Classical and Molecular Biology". Molecular Biology and Evolution. 5: 603–625. Platnick, N. I. (1985). "Philosophy and the transformation of cladistics revisited". Cladistics. 1(1): 87–94. Platnick, N. I. (1982). "Defining characters and evolutionary groups". Systematic Zoology. 31: 282–284. Scott-Ram, N. R. (1990). Transformed cladistics, taxonomy and evolution. Cambridge University Press.