Transformed cladistics

Transformed cladistics, also known as pattern cladistics is a proposed classification system within cladistics which excludes common ancestry from cladogram analysis. It was popularized by Colin Patterson in the 1980s, but has few modern proponents.

Patterns vs. processes

The standard approach to cladistics which traces back to Willi Hennig (1950) groups together organisms based on whether or not they share characters or character states that derived from a common ancestor. Transformed cladists instead maintain that cladistics should be free from the assumption of common descent or the theory of evolution (as a process) altogether, and based only on empirical data:

"If classifications (that is, our knowledge of patterns) are ever to provide an adequate test of theories of evolutionary processes their construction must be independent of any particular theory of process." (Platnick, 1979)

In other words, pattern cladists argue that the less information a classification presupposes, the fewer errors creep in, and greater objectivity results. They draw a distinction between patterns, which are observed, and processes, which may be inferred from patterns, but which should not be presupposed. Joseph Henry Woodger before the emergence of transformed cladistics as a school 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, 1945). Colin Patterson later wrote similarly:

"We must remember the distinction between the cart--the explanation--and the horse--the data. And where models are introduced in phylogenetic reconstruction, we should prefer models dictated by features of the data to models derived from explanatory theories." (Patterson, 1994)

Pattern cladists, like standard cladists, limit their classifications to nested sets (patterns) of synapomorphies, but they argue that the characters are irrespective to common ancestry:

"[T]o state a cladogram is a synapomorphy scheme invites the rejoinder that a cladogram must, therefore be a phyletic concept. Not so, for by ‘synapomorphy’ we mean ‘defining character’ of an inclusive taxon." (Nelson & Platnick, 1981)

Nelson & Platnick (1981) also note 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

"Pattern cladistics has remained on the fringe because of, first, its implausible assumption that there can be pure observation untainted by theory; and second, its rejection of the evolution assumption. Few systematists now think that a classification not based on evolutionary branching and history has any real signification or justification. The developing consensus is that Darwin was right – a natural classification must be genealogical."

Creationist distortion

Transformed cladistics does not deny common ancestry, rather it argues a logical precedence: theories regarding processes can only be formulated after observed patterns. Brady (1982, 1985) introduced the term explanandum for empirical patterns and explanans for process theory, writing: "by making our explanation into the definition of the condition [data] to be explained, we express not scientific hypothesis but belief". Creationists have distorted this to argue there are pattern cladists who are skeptical about whether evolution occurs.

Colin Patterson

In 1981, Patterson delivered a speech to a Systematics Discussion Group in the American Museum of Natural History. In the speech, Patterson asked: "Can you tell me anything about evolution, any one thing that is true?", and remarked:

"As I understand it, cladistics is theoretically neutral so far as evolution is concerned. It has nothing to say about evolution. You don’t need to know about evolution, or believe in it, to do cladistic analysis. All that cladistics demands is that groups have characters." (Patterson, 1981)

A creationist in the audience taped segments of Patterson's speech to imply he was "agnostic" on the subject of evolution. To his dismay, Patterson soon found his name quoted in creationist publications:

"I was too naive and foolish to guess what might happen: the talk was taped by a creationist who passed the tape to Luther Sunderland [...] Since, in my view, the tape was obtained unethically, I asked Sunderland to stop circulating the transcipt, but of course to no effect. There is not much point in my going through the article point by point. I was putting a case for discussion, as I thought off the record, and was speaking only about systematics, a specialized field. I do not support the creationist movement in any way, and in particular I am opposed to their efforts to modify school curricula. In short the article does not fairly represent my views. But even if it did, so what? The issue should be resolved by rational discussion, and not by quoting 'authorities,' which seems to be the creationists' principal mode of argument." (Letter from Colin Patterson to Steven W. Binkley, June 17, 1982)

"Unfortunately, and unknown to me, there was a creationist in my audience with a hidden tape recorder. A transcript of my talk was produced and circulated among creationists, and the talk has since been widely, and often inaccurately, quoted in creationist literature." (Patterson, 1994)

"Because creationists lack scientific research to support such theories as a young earth ... a world-wide flood ... or separate ancestry for humans and apes, their common tactic is to attack evolution by hunting out debate or dissent among evolutionary biologists. ... I learned that one should think carefully about candour in argument (in publications, lectures, or correspondence) in case one was furnishing creationist campaigners with ammunition in the form of 'quotable quotes', often taken out of context."

Modern proponents

A notable contemporary pattern cladist is Andrew Van Brower.

Bibliography

• 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.
• Nelson, G. (1985). "Outgroups and ontogeny". Cladistics. 1(1): 29-45.
• Nelson, G. (1989). "Cladistics and evolutionary models". Cladistics. 5(3): 275-289.
• Nelson, G. J., Platnick, N. I. (1981). Systematics and biogeography: cladistics and vicariance (Vol. 214). New York: Columbia University Press.
• 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.
• Patterson, C. (1994). "Null or minimal models". In: Models In Phylogeny Reconstruction. Scotland, R. W. , Siebert, D. J. (eds.). Systematics Association Special Volume; 173-192.
• Platnick, N. I. (1979). "Philosophy and the transformation of cladistics". Systematic Zoology. 28: 537–546.
• 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.
• Woodger, S. (1945). “On Biological Transformations”. In: Essays on Growth and Form. Le Gros Clark, W. E., Medawar, P. B (eds.). Oxford: Clarendon Press.