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Turtles All the Way Down?

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turtles

We ordered and have now just received our copy of Turtles as Hopeful Monsters: Origins and Evolution (University of Indiana Press), by paleontologist Olivier Rieppel at the Field Museum of Natural History in Chicago. Thus far, the book appears to be worth every dime. From the Amazon description:

Where do turtles hail from? Why and how did they acquire shells? These questions have spurred heated debate and intense research for more than two hundred years. Brilliantly weaving evidence from the latest paleontological discoveries with an accessible, incisive look at different theories of biological evolution and their proponents, Turtles as Hopeful Monsters tells the fascinating evolutionary story of the shelled reptiles. Paleontologist Olivier Rieppel traces the evolution of turtles from over 220 million years ago, examining closely the relationship of turtles to other reptiles and charting the development of the shell. Turtle issues fuel a debate between proponents of gradual evolutionary change and authors favoring change through bursts and leaps of macromutation.

We opened the book and started browsing. Here’s a great passage, picked more or less at random:

The problem of the transformational paradigm results — to use the terminology of Adolf Remane — from the nonexistence of a zero-value ancestor, one that would show no special adaptations of any kind to any particular environment, and for this reason would not have been viable (Nullwertahne). To derive a transformed, newly adapted structure from an ancestral one requires the ancestral structure to be primitive, or generalized, in all aspects relative to the derived structure. Such a totally generalized ancestral structure would, however, not be adapted to any specific mode of life. But every living organism must somehow be adapted to some sort of mode of life. This renders such a generalized, zero-value ancestor that is not adapted to any specific mode of life a biological impossibility.  (p. 122)

Reminds one, doesn’t it, of Stephen Meyer’s discussion in Darwin’s Doubt of the implausibility of the “shmoo” common ancestor for the Metazoa (pp. 111-113).  You’ve gotta love Rieppel’s term for this: “zero-value ancestor.”

Photo credit: Wolk9, via Pixabay.