June 29, 2005 | David F. Coppedge

Is Evo-Devo the Source of Endless Forms Most Beautiful?

Even staunch Darwinist Jerry A. Coyne (U of Chicago) thought this evolutionary book went overboard: Endless Forms Most Beautiful: The New Science of Evo-Devo by Sean B. Carroll (Norton, 2005), which he reviewed in Nature last week.1  (The title comes from a phrase at the end of Darwin’s Origin of Species.)  It’s a first-rate introduction to evo-devo written by an adept communicator, he feels, “but its faintly self-congratulatory message – that the most important problems in understanding the evolution of development have been solved – left me feeling uncomfortable.”
    In Coyne’s opinion, Carroll overplayed the evo-devo card.  Evo-devo assumes that gene regulation is the most important agent of evolutionary change; Coyne gives more place to gene duplication, genome duplication and ordinary old adaptive natural selection on genes and proteins.  Some of Coyne’s criticisms point out the problems inherent in all evolutionary theories.  Some examples:

  • Carroll presents his vision of the field without admitting that large parts of that vision remain controversial.  I would have appreciated a caveat or two, and non-scientists may mistakenly believe that Carroll presents the scientific consensus about evolution and development.
  • Carroll emphasizes throughout that the evolution of animal form and complexity results from three factors.
    1. The first is modularity of organization: the ground plan of bilateral animals involves repeated segments that can evolve independently….
    2. The second factor is that most animals share a small but similar set of ‘tool-kit genes’ that regulate the development of different modules…..
    3. But modularity and a shared genetic tool kit cannot by themselves account for “endless forms”, because conserved genes cannot explain diversity.  Carroll therefore repeatedly emphasizes his third thesis: that the main engine of evolution is not change in protein-coding genes but in the switches that control them.
  • The evidence for this critical hypothesis, however, rests more on inference than on observation or experiment.
  • Carroll also claims that proteins are resistant to evolutionary change: they are often involved in many pathways, and therefore a change in protein sequence, while enhancing one aspect of the protein’s many functions, could damage several others….
    But recent data cast doubt on this argument.  Humans have about 32,000 protein-coding genes, fruitflies only 13,000.  Clearly, the difference between these species involves the origin of new proteins: in fact, between 40% and 50% of our protein-coding genes have no known homologues in flies.  So one could argue that the evolution of form is very much a matter of teaching old genes to make new genes.  And, given the data, this cannot be difficult.
  • [Coyne argues for the evolutionary significance of gene duplication and adaptive selection.]  In contrast, the evidence for the adaptive divergence of gene switches is still thin.  The best case involves the loss of protective armour and spines in sticklebacks [see 06/18/2004 entry], both due to changes in regulatory elements. But these examples represent the loss of traits, rather than the origin of evolutionary novelties.
  • Carroll also gives many cases of different expression patterns of Hox genes associated with the acquisition of new structures (such as limbs, insect wings and butterfly eyespots), but these observations are only correlations. One could even argue that they are trivial.
  • Carroll’s correlations, however, do not compel us to believe that changes in these genes are the key factor in the evolution of such traits.  We now know that Hox genes and other transcription factors have many roles besides inducing body pattern, and their overall function in development – let alone in evolution – remains murky.
  • In the end, we simply don’t know the relative importance of protein and non-protein changes in creating biological diversity. (Emphasis added in all quotes.)

Coyne ends with both him and Carroll agreeing that evidence for evolution can be distorted: “Although Endless Forms Most Beautiful is a lucid and valuable summary of evo-devo, it does proclaim a clever but still unproved hypothesis as central to the evolutionary process.  As Carroll himself notes: ‘Simplification may indeed be necessary for news articles, but it can distort the more complex and subtle realities of evolutionary patterns and mechanisms.’”

1Jerry A. Coyne, “Switching on evolution: How does evo-devo explain the huge diversity of life on Earth?”, Nature 435, 1029-1030 (23 June 2005) | doi: 10.1038/4351029a.

Is evo-devo the evil-devil among Darwinists?  Like Satan, does he twist the word of lord Charlie?  Does he distort the evidence for his own nefarious ends?  Assuredly not; both Carroll and Coyne are on the same side, trying to oust God’s design from nature and account for everything by chance and biological laws.  What anti-creationist Coyne fails to realize is that he has cast both theories, evo-devo vs. standard Darwinism, in a deadly embrace.  Carroll wrote his book because of the weaknesses of standard Darwinism, and Coyne provided only bluffing assertions that standard Darwinism is sound, while arguing that evo-devo is just a clever idea that distorts the evidence and cannot really account for the diversity of life.  To argue otherwise requires simplification; i.e., the generous use of glittering generalities to create tall tales.  Neither evolutionary hypothesis can account for the complex and subtle realities of the living world mentioned in Coyne’s review – worms, lobsters, frogs, humans, chimpanzees, fruitflies, butterflies, mice, “the Cambrian explosion, the biology of dinosaurs, the brains of humans, and the striping of zebras” – and their “eyes, limbs, hearts and other complex structures” including “fly legs, fish fins and the tube feet of sea urchins.”
    But while calling Carroll’s evidence “thin,” Coyne is just as guilty of simplification: for example, look at this paragraph (our comments in brackets):

There are other ways beside gene duplication that proteins have evolved adaptively.  These include gene conversion [left unexplained], recruitment [personification fallacy] of genes to new functions (responsible for creating the antifreeze glycoproteins that allow fish to live in frigid waters) [see 05/13/2004 entry], exon shuffling (involved in the evolution of blood clotting factors) [Whoa!  Michael Behe showed how this is an irreducibly complex system unexplainable by evolution] and the addition of transposable elements to coding sequences [as if evolutionists understand this].  Finally, and simplest of all, we have many examples of adaptive changes of protein sequence between closely related species, including differences in the coat colour of mice [see “Peppered Mice?”, 04/18/2003], the digestive enzymes of herbivores, and the haemoglobins of high-altitude birds and mammals [do we just take his word for it?  Digestive enzymes and hemoglobins were already complex, functional protein machines before evolution tweaked them, even if it could].

Endless forms most beautiful speak of a Designer, not a blind process of evolution.  The shortcomings of Coyne’s view provide an opening for the claims of Carroll’s, and vice versa, such that they strangle each other, leaving both gasping for evidence.

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