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  Topic: Convergence, Causes and implications< Next Oldest | Next Newest >  

Posts: 319
Joined: May 2002

(Permalink) Posted: Dec. 26 2002,02:19   

A post from ICSID here:

Perhaps the reason that Hunter finds the evidence for common descent weak is that he misunderstands crucial points.

E.g., he has repeatedly alleged, without evidence, that designed objects will produce nested hierarchies.  But it just ain't so:



Although it is trivial to classify anything subjectively in a hierarchical manner, only certain things can be classified objectively in a consistent nested hierarchy. The difference drawn here between "subjective" and "objective" is crucial and requires some elaboration, and it is best illustrated by example. Different models of cars certainly could be classified hierarchically - perhaps one could classify cars first by color, then within each color by number of wheels, then within each wheel number by manufacturer, etc. However, another individual may classify the same cars first by manufacturer, then by size, then by year, then by color, etc. The particular classification scheme chosen for the cars is subjective. In contrast, human languages, which have common ancestors and are derived by descent with modification, generally can be classified in objective nested hierarchies (Pei 1949; Ringe 1999). Nobody would reasonably argue that Spanish should be categorized with German instead of with Portugese. The difference between classifying cars and classifying languages lies in the fact that, with cars, certain characters (for example, color or manufacturer) must be considered more important than other characters in order for the classification to work. Which types of car characters are more important depends upon the personal preference of the individual who is performing the classification. In other words, certain types of characters must be weighted subjectively in order to classify cars in nested hierarchies; cars do not fall into natural, unique, objective nested hierarchies.

Because of these facts, a cladistic analysis of cars will not produce a unique, consistent, well-supported tree that displays nested hierarchies. A cladistic analysis of cars (or, alternatively, a cladistic analysis of imaginary organisms with randomly assigned characters) will of course result in a phylogeny, but there will be a very large number of other phylogenies, many of them with very different topologies, that are as well-supported by the same data. In contrast, a cladistic analysis of organisms or languages will generally result in a well-supported nested hierarchy, without arbitrarily weighting certain characters (Ringe 1999). Cladistic analysis of a true genealogical process produces one or relatively few phylogenetic trees that are much more well-supported by the data than the other possible trees.

The degree to which a given phylogeny displays a unique, well-supported, objective nested hierarchy can be rigorously quantified. Several different statistical tests have been developed for determining whether a phylogeny has a subjective or objective nested hierarchy, or whether a given nested hierarchy could have been generated by a chance process instead of a genealogical process (Swofford 1996, p. 504). These tests measure the degree of "cladistic hierarchical structure" (also known as the "phylogenetic signal") in a phylogeny, and phylogenies based upon true genealogical processes give high values of hierarchical structure, whereas subjective phylogenies that have only apparent hierarchical structure (like a phylogeny of cars, for example) give low values (Archie 1989; Faith and Cranston 1991; Farris 1989; Felsenstein 1985; Hillis 1991; Hillis and Huelsenbeck 1992; Huelsenbeck et al. 2001; Klassen et al. 1991).

He also severely misunderstands convergence.  Convergence can only produce functionally-relevant similarities, because that is all that selection can "see".  Homologies, i.e. similarities between systems that are not necessary for functional similarity between systems, are what allows paleontologists to easily distinguish between these placental wolf and marsupial "wolf" skulls that cre8tionist posted in another thread:

I invite readers to go to The Thylacine Museum and look at the side-by-side comparison of 'wolf' skulls (with cool magnifier lense).

The caption reads:


Portrayed here are side-by-side images demonstrating the anatomical differences between the skulls of the Grey wolf (Canis lupus) and the thylacine (Thylacinus cynocephalus).  In the dorsal view, note that the thylacine has a much broader forehead than the wolf, and there are differences in the design of the zygomatic arches and brain case.  Also, the rostrum (snout) of the thylacine is far narrower than that of the wolf, and the thylacine has proportionately larger eye sockets which are rather more square in shape.  In the ventral view, one can easily see the great differences in dentition that  readily distinguish the two species as being members of distinct mammal groups.  The dentition of both species will be represented in greater detail on the following page.  Also visible in the ventral view is the thylacine's maxillary palatal vacuity (the two parallel openings in the roof of the mouth).  This is a feature that the wolf and other placental mammals do not have.

...on the next page...


Here I show some diagrams which I have prepared to illustrate the extreme difference in dental anatomy which exists between the thylacine and its placental counterpart, the wolf.  The images are portrayed at life size.  Although there are also a number of notable differences in post cranial skeletal structure between the thylacine and wolf, I felt that the dentition represented one of the most striking dissimilarities.  As you can easily see in the image of the maxilla, the thylacine has 8 top incisors, whereas the wolf has only 6.  In the mandible however, the thylacine and wolf have an equal number of incisors.  Another major difference is the presence of a specialized shearing tooth, the carnassial, in the wolf.  This tooth design is a trademark of the wolf and other members of the placental mammal family Carnivora.  Also make note that unlike the wolf, the thylacine lacks large grinding surfaces on its molars.  Altogether, the wolf has a complement of 42 teeth, and the thylacine 46.

I can't post the images here because they are copyright protected, but the differences in the tooth-numbering are dramatic.

All commonly-sighted cases of "uncanny convergence" in biology turn out, on investigation, to be externally impressive but superficial when you get down to details.  This is notably different from the kinds of things that have happened in aircraft design, e.g. the addition of (the same) transponders, GPS units, computers, TV screens, etc., to planes of widely different models.

This has been pointed out many times over the years, so I'm not sure why these cases still get seriously cited.


PS: There is also the interesting question of:

If the hypothesized IDer decided that there needed to be some carnivorous canine-type critters in Australia, why bother with all the genetic engineering that would be required, when a simple aboriginal boat sufficed to bring dingos to Australia only ~15,000 years ago?

Such ID puzzles are absolutely ubiquitous in biogeography.  To me they indicate strongly that whatever creativity made these wonderful adaptations was, for some odd reason, highly constrained so that "design information" could not be transmitted across deep water barriers and instead had to be re-invented from scratch each time the adaptation was "needed" in particular locations.  Strangely, such geographical constraints did not apply to flying birds, sea mammals, and other easily-dispersed organisms.

If you can find an ID theory that can explain this (and "the designer's actions are  mysterious" is not an explanation), I'll eat my hat.  If on the other hand you give natural selection the credit for these instances of creativity, then I guess natural selection can "design" things after all, and quite skillfully too...

  3 replies since Dec. 26 2002,02:19 < Next Oldest | Next Newest >  


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