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johnscanlon wrote:

"First the appeal to inclusivity and tolerance, including the remarkable statement that pheneticists are entitled to their beliefs. Anybody who still thinks that grouping by similarity is the best method of inferring phylogeny (tree-building) is simply mistaken in their belief. Tolerance can be taken too far."

Pheneticists hold the viewpoint that phylogenetic history is unknowable. Since history cannot be observed, it must therefore be inferred, as G. G. Simpson pointed out. The pheneticists therefore are correct to the extent that phylogenetic history cannot be determined with absolute certainty. Because of this belief, to which they are entitled, they thought that the best indicator of relationship would be overall similarity. Hence they have developed an elaborate set of mathematical techniques for measuring and quantifying morphological similarity. Pheneticists are simply not interested in building phylogenetic trees. Their phenogram simply tells us which species are morphologically most similar to each other. In some cases, overall similarity does work. For example, the common chimp is the closest relative of the pygmy chimp according to gestalt. In other cases, in which the rate of morphological evolution is different, this method does not work. For example, in terms of overall (morphological) similarity, Pan clusters with Gorilla, not Homo. But of course we know that Pan is actually closer to Homo phylogenetically than it is to Gorilla. The phenetic method therefore does have its merit and uses, although it is not infallible. In fact, it is sometimes more reliable than cladistic methodology since gestalt is sometimes better evidence for a close relationship than the one or a few characters with which the cladists may anchor a particular node in a cladogram.

Although the pheneticists are entitled to their believes, they are not entitled to impose their believes on others. Pheneticism has suffered a drastic decline, perhaps because it has now been shown that the pheneticists' fundamental belief (that phylogenetic history is unknowable) has now been all but falsified.

I do not think the concept that "true" phylogeny is recoverable has been falsified. There is too much unknown throughout the phylogenetic history.

I had this argument recently where someone was uncomfortable with a genus because it was monotypic, yet it actually had three described species. The point is that the geneticist in question failed to know that the taxa he worked on had two described species he was unaware of. How is this possible, well they were both fossils. But that does not mean they did not exist.

So of course this means that as fossil history is only partially recoverable, at best, the so called "true" phylogeny is not going to be recoverable. Of course a phylogeny based only only on living forms is so full of gaps it is not a "true" tree either.

The second difficulty is the isssue that many of the attempts to claim the "true" tree are based on molecular evidence which has only 4 states for each character and the most parsimonious view is that any of these states is equally probable (not entirely true I know, I am just making a point). Hence the overwriting and rewriting of the genetic characters would have to be taken as a given probability. So again the so called "true" tree is masked.

Personally I think phenetics has its uses, its a good tool for testing and developing field keys. Thats a good use and necessary and worthwhile. I am not going to develop trees with it though as its incapable of recognising homoplasy.

Cheers, Scott
Carettochelys.com

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Scott Thomson

If you believe you can or you can't you are always right.

>>Personally I think phenetics has its uses, its a good tool for testing and developing field keys. Thats a good use and necessary and worthwhile. I am not going to develop trees with it though as its incapable of recognising homoplasy.

I agree that phenetic approaches have a lot of uses, particularly at very low taxonomic levels, to visualise subtle patterns of variation and identify morphologically discrete clusters. In this context, I tend tho think of phenetics as making the bricks that phylogenetics uses to build a house.

Cheers,

Wolfgang
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Phenetic techniques were also employed effectively to test S. J. Gould's claim that morphological disparity among Burgess Shale arthropods is greater than that between living forms. Gould's claim was confirmed even though it was his opponents who were doing the testing.

In the future, it may be used in conjunction with molecular evidence to construct what Darwin calls the natural system, in which both propinquity of descent and degrees of modification are used to rank taxa.