David Tyler wonders Would Linnaeus have waved the banner of phylogenomics? He writes:

It may surprise some, but Newton did not pioneer physics with relativity in mind. It is not necessary to presuppose an equivalence between mass and energy to be a scholar working in this field.

Oh, that isn’t what he wrote. Here’s what he said:

It may surprise some, but Linnaeus did not pioneer systematics with the tree of life in mind. It is not necessary to presuppose a common ancestor for all living things to be a scholar working in this field.

One of the great scientific/philosophical battles of the 20th century was fought over how we should conduct taxonomy ? the naming and classification of life. Researchers since Carl von Linnť had been looking to basic similarity of form, selecting a particular trait or traits that the researcher finds meaningful in defining a group and moving on from there. Evolutionary taxonomy was an attempt by some of the creators of the Modern Synthesis of the 1940s to try to have those traits have some evolutionary significance, but it was not seen as necessary to make taxonomy reflect evolutionary history.


The development of rigorous statistical methods for evaluating multiple measurements pushed researchers away from evolutionary classifications, while the growing strength of evolutionary evidence began driving researchers to look for ways to make the form of a Linnaean hierarchy informative about evolutionary relationships. In the 1950s, Willi Hennig proposed this cladistic approach, while researchers like Sokal and Sneath at KU pushed the phenetic approach.

The cladistics wars raged hard for several decades, and many of my professors still seem ready to do battle for cladistics at the drop of a hat. The debate is interesting to look back on, because it drew heavily on questions from philosophy of science. Each side charged the other with being arbitrary, with being unscientific or proposing unfalsifiable claims. Reams of paper were blackened with ink, and friendships were destroyed. At the end, cladistics won out.

Cladistics is not so far from what Linnaeus did. Linnaeus selected traits based on intuition and his own interests and biases, using those traits to create a hierarchal classification. Hennig’s argument was that we should choose a range of characters, and construct classifications that minimize the number of character changes across evolutionary history. This winds up being roughly equivalent to replacing the arbitrary selection of characters with a process for selecting evolutionarily informative characters.

Classification has changed dramatically as a result of these techniques. Cladistics produces classifications which are empirically testable (new sets of characters ought to produce the same result, and if they don’t it’s necessary to understand why) and which are not dependent on the personal biases of a researcher. The hierarchy which once just provided a handy way to lump organisms together now becomes reflective of the history of life.

If Linnaeus were alive today, I imagine he’d be more concerned with getting out from under the stones of Uppsala Cathedral than with the latest advances in molecular systematics.

Update: Michael Egnor, brane sirjun, doesn’t think medical science, or science in general, has advanced since Aristotle. Or something. Plus Linnaeus died before Darwin was born. Quod aliquis erat demonstrandum (which hopefully translates as: “which was to demonstrate something”).

Comments

  1. #1 Coin
    March 27, 2007

    Creationism: Continuing to bring us the standard in state of the art science for the 18th century.

  2. #2 windy
    March 27, 2007

    Despite presupposing immutable species, Linnaeus managed to come across several intriguing details about life. Linnaeus was obsessed with a mutant type of Linaria that, according to his sexual classification system, was a completely new type of plant. Sadly, he mistook it for a hybrid when it was actually a mutant caused by a single gene. He also wondered whether he should have classified man with the apes. If only modern creationists were as open minded.

  3. #3 John Wilkins
    March 27, 2007

    Lots of myths about Linnaeus. First of all the tree of life was derived from his taxonomy. Initially it was a logical tree, but that, plus von Baer’s work on developmental differentiation, set up something that needed to be explained. Guess what explains it? Yup, Darwin’s evolutionary hypothesis of common descent.

    Second, Linnaeus allowed limited speciation via hybridisation later in life (the genus was Peloria). He had no trouble putting humans in Homo along with chimps, orangs, and various fabulous creatures that were human-like. It was Blumenbach and those who followed him who removed the chimps and later the gorillas to Pan and Pongo.

    There is a crucial difference between cladistics and Linnaeus – and that is in the use of many rather than a single criterion for differentiation (moreover, cladistic character matrices exclude functionally similar traits as potential homoplasies, or convergent characters). Linnaeus used, for plants, the fructification apparatus, and what is more he knew that was an artificial criterion. And so did everybody else. Linnaeus always sought after a “natural system” but never achieved it. Cladistic classification is a natural system.

  4. #4 windy
    March 27, 2007

    Second, Linnaeus allowed limited speciation via hybridisation later in life (the genus was Peloria).

    That’s the one I meant, but it isn’t really a hybrid! So Linnaeus was stuck looking for the other supposed parent species.

  5. #5 Josh
    March 27, 2007

    I agree that any sort of dichotomous classification system will give you some sort of tree. I think it’s fair to say, though, that the tree has no coherent interpretation except in light of evolution, and only then if the characters used are evolutionarily informative.

  6. #6 factician
    March 29, 2007

    I’m not terribly familiar with Linnaean history, but I thought that around that time evolution was largely understood to be important for his tree. Isn’t this true? Darwin’s contribution to science was not evolution. He didn’t even contribute the first mechanism for evolution (Lamarck suggested a mechanism decades earlier – a wrong mechanism, but a mechanism nonetheless). Darwin’s contribution was evolution by natural selection.

  7. #7 Jonathan Eisen
    March 30, 2007

    As the person who coined the term phylogenomics (before everyone got sick of new omics terms) I am proud to have it selected by creationists as an example of something to go after.

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