Such expressions as that famous one of Linnæus, and which we often meet with in a more or less concealed form, that the characters do not make the genus, but that the genus gives the characters, seem to imply that something more is included in our classification, than mere resemblance. I believe that something more is included; and that propinquity of descent,—the only known cause of the similarity of organic beings,—is the bond, hidden as it is by various degrees of modification, which is partially revealed to us by our classifications (Darwin, 1859, p. 413f).

Monday, 5 November 2007

Haeckel, Hennig and History: Evolving Thoughts and Words

John Wilkins, in his eminently readable and ever provocative blog Evolving Thoughts, presents an account of some historical matters relevant to Natural and Artificial Classifications, matters that might illuminate the differences of opinion between Joe Felsenstein and ourselves. To be sure, we differ on certain fundamental matters. But the issue of natural classifications is a subject that might repay closer attention and discussion. John's history is a cast of worthy individuals (Adanson, Linnaeus, Agassiz, Macleay, etc.), many who made worthy contributions to discovering the means with which to discover natural classification. They all, to one degree or another, had some sort of interpretation of that classification. They all, to one degree or another, had some sort of axe to grind. Never mind.

John moves on to note that " is with Haeckel and the early German paleontologists of the 20th century that phylogenetic relations become the core of classification, and we all know, of course, that Hennig defined a natural group as a monophyletic group." Haeckel is a something of a departure and one we see of significance. Here's Agassiz on Haeckel:
"It is not that I hold Darwin himself responsible for these troublesome consequences. In the different works of his pen, he never made allusion to the importance that his ideas could have for the point of view of classification. It is his henchmen who took hold of his theories in order to transform zoological taxonomy" (Agassiz, 1869: 375, our translation) (see also
Those henchmen included Haeckel. Most of Haeckel's genealogical trees ('phylogenies') were linear schemes of hypothesized relationships, with some taxa 'giving rise' to others, that is, paraphyletic groups not so much created by him (many were, of course) but retained and explained in terms of ancestry and descent, in terms of evolutionary relationships, relative to a particular model of change. It was to Hennig's credit that Haeckel's paraphyletic groups were exposed for what they were: empty conventions. And thus, a circle was closed and certain groups understood as not part of the discovery process of classification - or so it seemed. Haeckel's problem was taking a viewpoint (ancestry and descent) and interpreting classification from that perspective.

Now that's not a whole million miles away from the current viewpoint:
find a model of evolution and interpret the data from that point of view. Still, again, never mind. What comes shining through most of the earlier contributions to the debate is that, one way or another, Adanson, Linnaeus, Agassiz and Macleay, among others, did have a notion of the centrality of classification: homology. So when John suggests that "...It does not seem to me that cladistic classification is in possession of a notion of taxon that grounds its classifications" he omits consideration of homology. But he is not alone. The entire crop of books recently published dealing with the 'mathemetisation' of phylogeny do not deal with that subject at all. Thus, or so it seems to us, the 'mathemetisation' of classification (phylogeny) has lead to a profusion of artificial methods.

We finished a recent (as yet unpublished) paper with the following words, the first few are from Gareth Nelson:
'"What, then, of cladistics in relation to the history of systematics? If cladistics is merely a restatement of the principles of natural classification, why has cladistics been the subject of argument? I suspect that the argument is largely misplaced, and that the misplacement stems, as de Candolle suggests, from the confounding goals of artificial and natural systems" (Nelson, 1979, p. 20). Cladistics is concerned with homology, monophyly, evolutionary patterns, taxa (species), and natural classifications. That is, natural classification is concerned with relationships.'
PS. One of us [DMW] is a Londoner. We are aware (sometimes painfully) of the relationship between Australia and the UK capital city, the latter a onetime plentiful source of persons to inhabit the former. The 'relationship' between Australian's and Londoner's is such that when travelling in the United States a London accent is often mistaken for an Australian accent. We mention these facts, partly because the other half of this pair [MCE] is an Australian. And partly because the word 'Barny' is also said to originate from Cockney Rythming slang, as in Barny Rubble = trouble, and thus (if true) a mingling of Australian slang, London slang and American cartoon characters - words really do have a life of their own!

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