January 10, 2007 | David F. Coppedge

Are Evolutionists Converging on a Story of Vertebrates?

Here’s what the Linnean Society said in 1909, celebrating the 50th anniversary of Darwin’s Origin of Species, about the rise of vertebrates (fish, reptiles, amphibians, and mammals):

“When we return home and our friends gleefully enquire, ‘What then has been decided as to the Origin of Vertebrates?’, so far we seem to have no reply ready, except that the disputants agreed on one single point, namely that their opponents were all in the wrong.

Henry Gee, senior editor of Nature, quoted this remark by a participant at those meetings as a foil to his optimistic conclusion in a review article,1 where he crowed, “we have come a long way since 1909.”  Gee built his optimism around the reclassification of a hemichordate worm as the ancestor of all vertebrates based on studies by Lowe et al. in the 4 Jan issue of Nature.  Yet the basis for optimism was hard to find in the body of his review.  He indicated that many issues in this long-running problem in evolutionary biology are still only at the beginning of hopes for a solution, 98 years after the Linnean forfeit.  Some clips:

  • Molecular investigations of the origin of the dorso-ventral axis in an obscure marine invertebrate illuminate one of the longest-running debates in evolutionary biology – that over the origin of vertebrates.
  • Vertebrates are so different from other creatures that discovering their origins within the animal kingdom has always been problematic.  But molecular, developmental and genomic work on the sometimes obscure invertebrate relatives of vertebrates is prompting a re-evaluation of this vexed topic.
  • The quest to understand the deployment of the dorso-ventral axis has been one of the most enduring themes in the study of vertebrate origins.
  • This notion [a proposal by Geoffrey Saint-Hilaire in the 19th century] joined a list of seemingly eccentric theories about vertebrate origins that has been lengthening ever since.
  • Lowe and colleagues’ work on hemichordates adds welcome perspective…. More seriously, this new perspective will prompt a reappraisal of the many peculiarities of the development of the mouth that are seen in lampreys (primitive, jawless vertebrates) and amphioxus (a primitive, non-vertebrate chordate).  However, the central nervous systems of insects and chordates – and indeed those of all animals that have them –represent a range of solutions in which the location is governed by the BMP-Chordin axis, if not directly specified by them.
  • The status of amphioxus itself has likewise been a matter of debate….
  • Of course, sequencing a genome is not the same as understanding the evolution of morphological novelties. But we have come a long way since 1909….

In the end, his article really amounted to a brief look at one new perspective in a long-standing debate, contingent upon results of more genomic studies.
    Meanwhile, in the same issue of Nature,2 some Finnish scientists in conjunction with the Denver Museum studied mammal teeth using a “homology-free” approach (see “Homology for Dummies,” 05/05/2004).  Their method did not consider common ancestry, but just looked at tooth shape of carnivores and their prey.  They devised rules for categorizing tooth phenotype based primarily on diet.  It was striking to them how similar some teeth looked considering how long ago their lineages diverged according to evolutionary theory:

Cat teeth and mouse teeth, for example, are fundamentally distinct in shape and structure as a result of independent evolutionary change over tens of millions of years.  There is difficulty in establishing homology between their tooth components or in summarizing their tooth shapes, yet both carnivorans and rodents possess a comparable spectrum of dietary specializations from animals to plants.  Here we introduce homology-free techniques to measure the phenotypic complexity of the three-dimensional shape of tooth crowns.  In our geographic information systems (GIS) analysis of 441 teeth from 81 species of carnivorans and rodents, we show that the surface complexity of tooth crowns directly reflects the foods they consume.  Moreover, the absolute values of dental complexity for individual dietary classes correspond between carnivorans and rodents, illustrating a high-level similarity between overall tooth shapes despite a lack of low-level similarity of specific tooth components.  These results suggest that scale-independent forces have determined the high-level dental shape in lineages that are widely divergent in size, ecology and life history.

It seems that for teeth, regardless of evolutionary history, you are what you eat.


1Henry Gee, “Developmental biology: This worm is not for turning,” Nature 445, 33-34 (4 January 2007) | doi:10.1038/445033a.
2Evans et al, “High-level similarity of dentitions in carnivorans and rodents,” Nature 445, 78-81 (4 January 2007) | doi:10.1038/nature05433.

How long do you give a scientific hypothesis time to be established?  Five years?  Ten years?  Has 148 been enough yet?  Darwin’s gangsters have been scratching their heads for over a century to put the pieces of the vertebrate puzzle together.  Despite Henry Gee’s confident optimism, they are still at square one.  (This same Henry Gee is an ardent foe of Darwin critics and rarely prints their letters in his Huxley bulldog rag.)
    Their failure to explain the origin of vertebrates and every other plant and animal group did not stop the Darwinists from celebrating the 50 year anniversary of the Origin, and the 100th year anniversary in 1959 (a whopper of bombast, bravado and bluffing with enough hot air to lift a tank).  Now, plans are already underway for a huge Darwin year of celebrations in 2009.  Hate to rain on your parade, fellas, but how about a little evidence that your theory fits the observational facts?
    Meanwhile, science marches on without need for approaches based on evolutionary homology.  The researchers in the second paper assumed evolution, but did not use it in their work.  They did science the old-fashioned way: measured things about teeth and related them to observable factors like what the animals eat.  Darwin’s tinker-fairy tales provided little practical help in their actual work.  The only influence of Darwinian thinking was a surprise effect: “Shazam, look how similar these teeth look after 65 million years of independent evolution!”  Chew on that thought.  Then put it where it belongs – in the spittoon.

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Categories: Mammals

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